Common variable immunodeficiency is a primary antibody deficiency disorder, often presenting in late childhood or adolescence, characterized by significantly reduced serum immunoglobulins (IgG, IgA, and/or IgM) and impaired vaccine responses, leading to recurrent sinopulmonary and gastrointestinal infections.

Common Variable Immunodeficiency (CVID) in Paediatrics

Common Variable Immunodeficiency (CVID) — let's break down the name:

"Common" — it is the most frequently diagnosed clinically significant primary immunodeficiency (PID)
"Variable" — the clinical presentation is heterogeneous; patients can present with infections, autoimmunity, lymphoproliferation, granulomatous disease, or malignancy in any combination
"Immunodeficiency" — the core defect is a failure of adequate immunoglobulin production

CVID is a heterogeneous group of disorders characterised by late-onset hypogammaglobulinaemia that presents often in childhood, adolescence, or early adulthood. ^[1]^[2]

Formally, CVID is defined by the European Society for Immunodeficiencies (ESID) 2019 / International Consensus (ICON 2016) criteria as:

Marked decrease in IgG (at least 2 SD below age-matched mean), measured on at least two occasions ≥ 3 weeks apart
Plus low IgA and/or low IgM
Plus impaired vaccine responses (poor response to protein and/or polysaccharide antigens)
Plus exclusion of other defined causes of hypogammaglobulinaemia
Plus age ≥ 4 years at diagnosis (to distinguish from transient hypogammaglobulinaemia of infancy)

Why age ≥ 4 years?

Before age 4, transient hypogammaglobulinaemia of infancy (THI) is common — maternal IgG wanes by 4–6 months, and the infant's own Ig production may be physiologically delayed. Labelling a child as CVID before age 4 risks misdiagnosis. However, clinical suspicion should still be raised earlier if features are severe.

2. Epidemiology

The most frequent primary immunodeficiency ^[1]^[2]^[3]
Estimated prevalence: 1 in 25,000–50,000 in Caucasian populations
In Hong Kong / East Asian populations, CVID is less common than in Western cohorts (selective IgA deficiency, the most common PID globally, is rarer in Chinese populations; similarly CVID prevalence is lower but still the most common clinically significant antibody deficiency seen in paediatric immunology clinics)
Among all PIDs, predominantly antibody deficiencies account for ~36.3% of cases, and CVID is the largest contributor to this category ^[4]

Bimodal peak: first peak in childhood (ages 5–10 years), second peak in early adulthood (ages 20–30 years)
Median age at diagnosis is often delayed (6–8 years after symptom onset), which is a major clinical problem — diagnostic delay leads to irreversible end-organ damage (e.g., bronchiectasis)
Late-onset hypogammaglobulinaemia that presents often in childhood/adolescence/early adulthood ^[1]^[2]

Roughly equal M:F ratio (unlike X-linked agammaglobulinaemia which is male-only)
This is because CVID is mostly sporadic or autosomal (both AD and AR patterns described)

In children, CVID must be distinguished from transient hypogammaglobulinaemia of infancy and other monogenic antibody deficiencies (XLA, hyper-IgM syndromes)
Children with CVID tend to have more autoimmune and lymphoproliferative complications compared to those with later-onset disease

Risk Factor	Explanation
Family history of PID	~10–25% of CVID patients have a first-degree relative with some form of immunodeficiency (often selective IgA deficiency — these conditions exist on a spectrum)
Consanguinity	Increases risk of autosomal recessive forms
HLA associations	Certain HLA haplotypes (HLA-DR3, HLA-B8, HLA-A1) are overrepresented — suggests MHC-linked genetic susceptibility
Family history of autoimmunity	Autoimmune diseases cluster in families of CVID patients

Selective IgA Deficiency ↔ CVID Spectrum

Selective IgA deficiency is the most common PID overall. Some patients with selective IgA deficiency progress to CVID over time, and both conditions can occur in the same family. They may share genetic susceptibility loci (e.g., TACI mutations). Think of them as a continuum of B-cell maturation defects.

4. Anatomy and Immunology Review — Why CVID Matters

To understand CVID, you must understand the normal pathway of B-cell maturation and antibody production:

Key steps where CVID goes wrong:

B cells are present (unlike XLA where B cells are absent) — in CVID, B-cell numbers are usually normal or mildly reduced
The defect is in B-cell differentiation and maturation — specifically the terminal differentiation of B cells into plasma cells and the class-switch recombination process
This leads to defective immunoglobulin production despite adequate B-cell numbers ^[1]^[4]

B-cell class switching requires T-cell help via:
- CD40L (on T cells) – CD40 (on B cells) interaction → signals the B cell to undergo class switch recombination
- ICOS (on T cells) – ICOS-L (on B cells) → co-stimulatory signal for germinal centre reactions
- Cytokines (IL-4, IL-21) from T follicular helper (Tfh) cells
In many CVID patients, there are T-cell abnormalities too — reduced T-cell proliferation, skewed CD4/CD8 ratio, reduced Tfh cells — explaining why CVID is not purely a B-cell disease

Commonly cause sinopulmonary and GI infections because (1) sites where most Ig deposits, and (2) open to external environment ^[4]

IgA is the predominant immunoglobulin at mucosal surfaces (respiratory tract, GI tract)
IgG opsonises encapsulated bacteria in the lungs and bloodstream
When both are deficient, the respiratory and GI mucosa are left unprotected → recurrent sinusitis, pneumonia, otitis media, bronchiectasis, chronic diarrhoea

5. Aetiology and Pathophysiology

CVID is genetically heterogeneous. In most cases (~85–90%), no single causative gene is identified. However, mutations have been described in four genes: ICOS, CD19, BAFF-R, and TNFRSF13B [also known as transmembrane activator and CAML interactor (TACI)], together associated with 10–15% of CVID cases ^[1]^[2]^[3].

Gene	Protein	Inheritance	Role	Consequence of Mutation
TNFRSF13B	TACI	AD or AR	Receptor on B cells for BAFF and APRIL → promotes B-cell survival, class switching, and T-independent responses	Required for final maturation of B-lymphocytes; 10–15% of CVID patients ^[2]^[3]
ICOS	ICOS (Inducible T-cell CO-Stimulator)	AR	Co-stimulatory molecule on T cells → essential for germinal centre reaction and Tfh function	Loss of T-cell help → impaired B-cell class switching
CD19	CD19	AR	B-cell co-receptor → lowers the threshold for B-cell activation	Impaired B-cell signalling and activation
BAFF-R (TNFRSF13C)	BAFF receptor	AR	Receptor for BAFF (B-cell activating factor) → promotes B-cell survival	Reduced B-cell survival; variable clinical expression; low IgG and IgM ^[5]

More recently identified genes (with expanding next-generation sequencing):

NFKB1, NFKB2 (AD) — transcription factors critical for B-cell development and immune regulation
PIK3CD (AD, gain-of-function) — Activated PI3Kδ syndrome (APDS); severe bacterial infections, lymphadenopathy, lymphoproliferation, lymphoma; EBV+/CMV viraemia, autoimmunity ^[5]
PIK3R1 — regulatory subunit of PI3K
CTLA-4 (AD) — immune checkpoint; haploinsufficiency → autoimmunity + hypogammaglobulinaemia
LRBA (AR) — regulates CTLA-4 trafficking; deficiency causes CVID-like phenotype with prominent autoimmunity
IKAROS (IKZF1) (AD) — transcription factor for lymphocyte development

High Yield — Genetic Basis

For exams: remember TACI (TNFRSF13B) as the most commonly implicated gene, found in 10–15% of CVID patients ^[1]^[2]^[3]. The other three classic genes (ICOS, CD19, BAFF-R) are very rare. Most CVID remains genetically undefined.

Key pathophysiological concepts:

Impaired B-cell differentiation → hypogammaglobulinaemia
- Impaired B cell differentiation → defective Ig production ^[4]
- ↓↓↓IgG, ↓IgA/E ^[4]
- B cells are present but cannot complete terminal differentiation into antibody-secreting plasma cells
- Switched memory B cells (CD27+IgD−IgM−) are characteristically absent or markedly reduced
- Switched memory B cell absent → more prone to recurrent respiratory infections and development of bronchiectasis ^[6]
T-cell dysfunction (present in ~50% of CVID patients)
- Reduced CD4+ T cells, inverted CD4:CD8 ratio
- Impaired T-cell proliferative responses
- Reduced regulatory T cells (Tregs) → contributes to autoimmunity
- Expanded CD21low B cells → marker of chronic immune activation
Immune dysregulation → autoimmunity and lymphoproliferation
- Loss of peripheral tolerance mechanisms
- Defective Treg function → self-reactive lymphocyte escape
- Chronic antigenic stimulation from recurrent infections → polyclonal lymphoproliferation
Granulomatous disease
- Non-caseating granulomas (resembling sarcoidosis) found in lungs, lymph nodes, liver, spleen
- Thought to result from aberrant macrophage/T-cell response to persistent immune stimulation
- Granulomatous disease in 8–22% ^[1]
Malignancy predisposition
- Chronic immune activation + impaired immune surveillance → lymphomagenesis
- Increased risk of gastrointestinal and lymphoid malignancies ^[1]^[2]
- Non-Hodgkin lymphoma is the most common malignancy in CVID ^[4]

Feature	XLA (Bruton)	CVID
Inheritance	X-linked recessive	Mostly sporadic; AD or AR
Sex	Males only	Males and females equally
Gene defect	BTK (Bruton tyrosine kinase)	Multiple/unknown
B cells	Absent (↓B cells) ^[4]	Present (normal or mildly low)
Immunoglobulins	Pan-hypoglobulinaemia ^[4]	↓↓↓IgG, ↓IgA/E (IgM may be low or normal) ^[4]
Age of onset	After 4–6 months (when maternal IgG wanes) ^[4]	Older children, adolescents, young adults
Tonsils/lymph nodes	Absent ^[4]	Present (may be enlarged!)
Autoimmunity	Uncommon	Common (~25%)
Lymphoproliferation	No	Yes (~1/3)

Exam Pearl — XLA vs CVID

A common exam trap: XLA patients have absent tonsils and lymph nodes because they have no B cells to populate lymphoid tissue. CVID patients have B cells — they just don't function properly — so lymphoid tissue is present and may even be enlarged (lymphoproliferation). If you see a boy with absent tonsils + agammaglobulinaemia → think XLA. If you see a child with splenomegaly, lymphadenopathy + hypogammaglobulinaemia → think CVID.

6. Classification

CVID falls under Category III: Predominantly Antibody Deficiencies in the IUIS (International Union of Immunological Societies) classification of inborn errors of immunity ^[5].

Group	Switched Memory B cells (CD27+IgD−IgM−)	Clinical Significance
Group Ia	< 0.4% of B cells + expanded CD21low B cells	Highest risk of splenomegaly, autoimmunity, granulomatous disease
Group Ib	< 0.4% of B cells, normal CD21low	Intermediate risk
Group II	≥ 0.4% (normal switched memory B cells)	Mainly infectious complications, better prognosis

This is the more current classification, incorporating:

Switched memory B cells (smB+ vs smB−)
CD21low expansion (≥ 10% of B cells)
Transitional B cell expansion (≥ 9% of B cells)

Clinical relevance: Patients with smB− (absent switched memory B cells) have:

More prone to recurrent respiratory infections and development of bronchiectasis ^[6]
Higher rates of splenomegaly, granulomatous disease, autoimmune cytopenias

From a pragmatic clinical standpoint, CVID patients can be grouped by their dominant phenotype:

Infection-only phenotype (~65–70%) — best prognosis
Autoimmune phenotype (~25%) — cytopenias, organ-specific autoimmunity
Lymphoproliferative phenotype (~30%) — splenomegaly, lymphadenopathy, granulomatous-lymphocytic interstitial lung disease (GLILD)
Malignancy phenotype (~5–10%) — lymphoma, gastric cancer
Combined/overlapping phenotype — many patients have features from multiple groups

High Yield Classification Point

Patients with the infection-only phenotype have the best prognosis. Patients with autoimmune cytopenias, lymphoproliferation, or granulomatous disease have significantly worse outcomes and higher mortality. The presence of absent switched memory B cells is a poor prognostic marker ^[6].

7. Clinical Features

Before diving into CVID-specific features, recall the general approach to suspecting primary immunodeficiency:

"SPUR" infections: Disproportionate frequency, Disproportionate severity, Unusual microbes, Unusual sites of infection, Unusual clinical presentation ^[7]

7.2 Symptoms (with Pathophysiological Basis)

This is the hallmark presentation. Recurrent respiratory tract infections with the development of bronchiectasis ^[1]^[2].

Symptom	Pathophysiological Basis
Recurrent sinusitis	IgA deficiency → loss of mucosal immunity in paranasal sinuses; IgG deficiency → poor opsonisation of encapsulated bacteria (S. pneumoniae, H. influenzae)
Recurrent otitis media	Same mucosal IgA deficiency + Eustachian tube colonisation
Recurrent pneumonia	Loss of opsonising antibodies → encapsulated bacteria proliferate in lower airways → repeated pneumonias → progressive airway destruction
Chronic productive cough	Bronchiectasis develops from repeated infections → permanent dilation of bronchi → impaired mucociliary clearance → chronic sputum production
Chronic or intermittent diarrhoea ^[1]^[2]	IgA deficiency at GI mucosa → susceptibility to Giardia lamblia, norovirus, Campylobacter; also nodular lymphoid hyperplasia of small bowel → malabsorption
Failure to thrive / poor growth (paediatric-specific)	Chronic infection + malabsorption + increased metabolic demand → caloric deficit → growth faltering; must be plotted on growth charts and compared to age-appropriate centiles

Common pathogens in CVID (antibody deficiency pattern):

Encapsulated bacteria (S. pneumoniae, H. influenzae), Giardia, Enterovirus ^[4]

Mycoplasma pneumoniae is also common
Opportunistic infections (PJP, CMV, etc.) are NOT typical of isolated antibody deficiency — if present, suspect combined immunodeficiency

Paediatric Pearl — Growth and Development

In paediatric CVID, always assess:

Growth: Plot weight, height/length, and head circumference on age-appropriate growth charts (WHO for < 2 years, CDC or local charts for older children). Look for crossing centiles downward.
Development: Chronic illness and recurrent hospitalisations can impair developmental milestones. Assess gross motor, fine motor, language, and social milestones at each visit.
Nutrition: Chronic diarrhoea → malabsorption of fat-soluble vitamins (A, D, E, K), iron, zinc → assess nutritional status.

Autoimmune phenomena such as idiopathic thrombocytopenic purpura and autoimmune haemolytic anaemia in up to 25% ^[1]^[2].

Symptom	Pathophysiological Basis
Easy bruising / petechiae / mucosal bleeding	Immune thrombocytopenia (ITP) — loss of immune tolerance → anti-platelet antibodies (anti-GPIIb/IIIa) → platelet destruction in spleen ^[8]
Fatigue, pallor, jaundice	Autoimmune haemolytic anaemia (AIHA) — anti-RBC antibodies → extravascular haemolysis in spleen; when ITP + AIHA co-occur = Evans syndrome
Joint pain and swelling	Rheumatoid-like inflammatory arthritis — immune complex deposition and/or loss of tolerance to synovial antigens
Skin rashes (various)	Vitiligo, alopecia areata, psoriasis-like lesions — autoimmune targeting of skin components
Cytopenias	Autoimmune neutropenia can also occur — anti-neutrophil antibodies

In paediatrics, autoimmune cytopenias may be the presenting feature of CVID, even before recurrent infections become obvious. Always check immunoglobulins in a child with unexplained ITP or AIHA, especially if recurrent or refractory.

Polyclonal lymphoproliferation with splenomegaly, lymphadenopathy, or nodular lymphoid hyperplasia of the small bowel occurs in approximately 1/3 of patients ^[1]^[2].

Symptom	Pathophysiological Basis
Abdominal distension / left upper quadrant fullness	Splenomegaly — reactive lymphoid hyperplasia due to chronic antigenic stimulation + autoimmune cytopenias causing splenic sequestration
Palpable lymph nodes (generalised lymphadenopathy)	Polyclonal B-cell and T-cell proliferation in lymph nodes; must distinguish from lymphoma (biopsy may be needed)
Abdominal pain, bloating, malabsorption	Nodular lymphoid hyperplasia of small bowel → mucosal distortion → malabsorption
Dyspnoea, chronic cough (non-infective)	Granulomatous-lymphocytic interstitial lung disease (GLILD) — granulomas + lymphocytic infiltration of lung parenchyma; found in ~8–22% ^[1]; can be progressive and cause restrictive lung disease

Granulomatous disease in 8–22% ^[1]^[2].

Symptom	Pathophysiological Basis
Cough, dyspnoea (insidious onset)	Pulmonary granulomas (non-caseating, sarcoid-like) + lymphocytic interstitial pneumonitis → GLILD
Hepatomegaly, abnormal LFTs	Hepatic granulomas → granulomatous hepatitis
Splenomegaly	Splenic granulomas
Lymphadenopathy	Granulomatous lymphadenitis
Skin nodules	Cutaneous granulomas

Why granulomas? The exact mechanism is unclear, but the leading hypothesis is:

Defective humoral immunity → failure to clear antigens → persistent antigenic stimulation → macrophage activation → granuloma formation
Resembles sarcoidosis histologically but is a distinct entity

Symptom	Pathophysiological Basis
Chronic diarrhoea ^[1]^[2]	Giardiasis (due to IgA deficiency), nodular lymphoid hyperplasia, IBD-like inflammation, small bowel bacterial overgrowth
Steatorrhoea	Fat malabsorption from villous atrophy (sprue-like changes) or Giardia
Abdominal pain	Nodular lymphoid hyperplasia, IBD-like colitis
Weight loss / poor weight gain	Malabsorption + chronic inflammation + increased metabolic demands

CVID can present with IBD-like disease — some CVID patients develop a Crohn's-like or UC-like colitis. Always check immunoglobulins in paediatric IBD, especially if refractory to standard treatment.

Increased risk of gastrointestinal and lymphoid malignancies ^[1]^[2]^[4].

Malignancy	Details
Non-Hodgkin lymphoma ^[4]	Most common CVID-associated malignancy; B-cell NHL predominates; risk is ~5–12× general population
Gastric cancer / gastric adenocarcinoma	Associated with chronic atrophic gastritis (autoimmune) → intestinal metaplasia → dysplasia → carcinoma
Other lymphoid malignancies	Hodgkin lymphoma, EBV-driven lymphoproliferative disorders

Sign	Pathophysiological Basis
Failure to thrive / growth faltering (paediatric)	Chronic infection + malabsorption + inflammation → caloric deficit
Tonsils and lymph nodes present (contrast to XLA)	B cells are present in CVID (unlike XLA where they are absent) → lymphoid tissue develops normally
Generalised lymphadenopathy	Polyclonal lymphoproliferation; must exclude lymphoma
Splenomegaly	Lymphoproliferation + autoimmune sequestration
Hepatomegaly	Granulomatous hepatitis, nodular regenerative hyperplasia
Clubbing	Chronic bronchiectasis → chronic hypoxia and inflammation → digital clubbing
Inspiratory coarse crackles	Bronchiectasis — secretion pooling in permanently dilated airways
Signs of anaemia (pallor, tachycardia)	AIHA or iron deficiency from malabsorption
Petechiae, purpura, bruising	ITP (autoimmune thrombocytopenia)
Jaundice	Haemolytic anaemia (AIHA)
Skin granulomas / nodules	Granulomatous disease
Joint swelling / deformity	Inflammatory arthritis
Evidence of chronic sinusitis	Mucosal oedema, nasal polyps, post-nasal drip
Chronic ear disease	Tympanic membrane scarring, perforation from recurrent otitis media

Humoral (antibody) deficiency timing: present after 4–6 months due to maternal IgG depletion ^[4]

In the first 4–6 months of life, the infant is protected by transplacentally acquired maternal IgG
After this wanes, if the infant cannot produce its own IgG → infections begin
However, CVID typically presents later than XLA (school-age rather than infancy), because the B-cell defect in CVID is partial/progressive rather than absolute
Many children with CVID have a period of seemingly normal health before infections accumulate

8. Initial Evaluation Framework

Initial evaluation: Exclude secondary immunodeficiency (diabetes, HIV, protein-losing states, CKD, malignancy, immunosuppression, drugs, structural defects), look for SPUR infections, obtain salient history (phenotype, age of presentation, progression, pathogen pattern, infection location, features of immune dysregulation, family tree 3 generations), and perform first-line investigations ^[7]

First-line investigations:

CBC and differentials

Absolute lymphocyte count

Liver and renal function tests

Protein and globulin level

Acute phase reactants (ESR/CRP) — ↓ESR if low globulin/fibrinogen

Immunoglobulin profile (including IgE)

Serum and urine electrophoresis

C3/C4

ANA ± autoimmune serologies

HIV status (Antigen or PCR)

CXR / CT Thorax / Lung function ^[7]

Why ↓ESR in Hypogammaglobulinaemia?

ESR depends on the aggregation of red blood cells, which is promoted by large proteins — especially fibrinogen and immunoglobulins (particularly IgM). In CVID, immunoglobulins are low → reduced rouleaux formation → paradoxically low ESR even in the presence of infection or inflammation. A low ESR in a patient with active infection should make you think of hypogammaglobulinaemia!

Lab findings in a CVID case:

HIV negative

Tetanus, HAV, HBV antibodies negative despite vaccination (impaired vaccine responses — a diagnostic criterion)

Isohaemagglutinin positive (some residual antibody production)

Lowish lymphocyte count (0.85–0.96 × 10⁹/L), subset percentages normal

Lymphocyte proliferation normal

Induced expression of CD40L normal (excludes hyper-IgM syndrome type 1)

Neutrophil respiratory burst function normal (excludes CGD)

Switched memory B cells absent ^[6]

Marker	What It Means	In CVID
CD19+ B cells	Total B-cell count	Usually present (> 1%) — differentiates from XLA where B cells are absent ^[5]
CD27+IgD−IgM− (switched memory B cells)	B cells that have undergone class switching in germinal centres	Absent or markedly reduced — correlates with worse clinical phenotype ^[6]
CD21low B cells	Chronically activated, exhausted B cells	May be expanded — marker of immune dysregulation
Transitional B cells	Recent bone marrow emigrants	May be expanded

When taking a history from a child's caregivers:

Infection history — chronological catalogue of all infections:
- Type (URTI, LRTI, GI, skin, UTI)
- Frequency (how many per year? how many courses of antibiotics?)
- Severity (hospitalisation? IV antibiotics? ICU?)
- Unusual organisms (Giardia, Mycoplasma, Enterovirus)
- Unusual sites
Immunisation history — critically important:
- Has the child received all age-appropriate vaccines?
- Any adverse reactions to live vaccines? (important for combined immunodeficiencies — live vaccines are contraindicated in T-cell defects)
- Did the child mount serological responses to vaccines? (check anti-tetanus, anti-hepatitis B antibody titres)
Growth and development — plot on growth charts; assess developmental milestones
Autoimmune features — cytopenias, rashes, joint complaints
Family history — plot family tree for 3 generations ^[7]:
- Any relatives with recurrent infections, autoimmune disease, immunodeficiency, early death from infection?
- Consanguinity ^[7]
Drug history — exclude drug-induced hypogammaglobulinaemia:
- Rituximab (anti-CD20 → B-cell depletion)
- Anti-epileptics (carbamazepine, phenytoin)
- Systemic corticosteroids
- Other immunosuppressants
Feeding history (infants/toddlers) — breast or formula? (breast milk provides some passive immunity via secretory IgA)

Communication with Child and Caregivers

Use age-appropriate language when speaking to the child
For younger children (< 7 years), most history comes from caregivers
For adolescents, ensure confidential time to discuss concerns
Explain investigations in terms the family understands
Address parental anxiety about immunodeficiency diagnosis

Feature	XLA	CVID	Hyper-IgM Syndrome	Selective IgA Deficiency
Inheritance	XLR	Sporadic/AD/AR	XLR (Type 1, CD40L) or AR	Sporadic/AD
Gene	BTK	Multiple/unknown	CD40L (Type 1)	Unknown
B cells	Absent	Present	Present	Present
IgG	↓↓↓	↓↓↓ ^[4]	↓	Normal
IgA	↓↓↓	↓ ^[4]	↓	↓↓↓
IgM	↓↓↓	↓ or normal	↑	Normal
IgE	↓	↓ ^[4]	↓	Normal
Tonsils	Absent	Present	Present	Present
Age of onset	4–6 months	> 4 years (usually)	4–6 months	Any (often asymptomatic)
Autoimmunity	Rare	Common (25%)	Less common	Occasionally
Lymphoproliferation	No	Yes (33%)	No	No
Malignancy risk	Minimal	Yes (lymphoma, GI)	Yes (lymphoma, hepatic)	Minimal
Prevalence	Rare	Most common severe PID ^[1]^[2]	Rare	Most common PID ^[4]

High Yield Summary

Definition: CVID is a heterogeneous group of primary immunodeficiencies characterised by late-onset hypogammaglobulinaemia (↓↓↓IgG, ↓IgA ± ↓IgM) with impaired vaccine responses, presenting in childhood/adolescence/early adulthood.

Most common clinically significant PID (selective IgA deficiency is the most common PID overall, but CVID is the most common severe antibody deficiency).

Pathophysiology: Impaired B-cell differentiation → defective immunoglobulin production. B cells are PRESENT (unlike XLA). Switched memory B cells are characteristically absent.

Genetics: TACI (TNFRSF13B) is the most commonly implicated gene (~10–15%), along with ICOS, CD19, BAFF-R. ~85–90% have no identified monogenic cause.

Clinical features — 5 phenotypes:

Infections (~90%): sinopulmonary (sinusitis, pneumonia → bronchiectasis), GI (diarrhoea, Giardia), otitis media
Autoimmunity (~25%): ITP, AIHA, Evans syndrome, inflammatory arthritis
Lymphoproliferation (~33%): splenomegaly, lymphadenopathy, nodular lymphoid hyperplasia of small bowel
Granulomatous disease (8–22%): GLILD, granulomatous hepatitis
Malignancy: non-Hodgkin lymphoma, gastric cancer

Key pathogens: Encapsulated bacteria (S. pneumoniae, H. influenzae), Giardia, Enterovirus, Mycoplasma.

First-line Ix: CBC + diff, absolute lymphocyte count, protein/globulin, Ig profile (IgG/A/M/E), vaccine responses, HIV test, CXR. B-cell subsets (switched memory B cells).

XLA vs CVID: XLA = absent B cells, absent tonsils, males only, BTK mutation. CVID = B cells present, tonsils present, M=F, heterogeneous genetics.

Paediatric priorities: Growth assessment, developmental monitoring, age-appropriate communication, family-centred care, age-specific normal values for immunoglobulins.

Active Recall - CVID Overview, Epidemiology, Pathophysiology, and Clinical Features

^[1] Lecture slides: Investigations of Imm Disorders 2025.pdf (p15 — CVID section) ^[2] Senior notes: Jerry's immunodeficiencies.pdf (CVID section) ^[3] Senior notes: Jerry's immunodeficiencies.pdf (TACI gene section) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p410 — Primary Immunodeficiency) ^[5] Lecture slides: Investigations of Imm Disorders 2025.pdf (p21 — Predominantly Antibody Deficiencies classification) ^[6] Lecture slides: Investigations of Imm Disorders 2025.pdf (p14 — CVID case lab results) ^[7] GC Lecture slides: GC 096. Why do I always get sick.pdf (p21 — Initial evaluation) ^[8] Senior notes: Ryan Ho Haemtology.pdf (p117 — ITP and CVID as secondary cause)

Differential Diagnosis of CVID in Paediatrics

CVID is famously a diagnosis of exclusion — you cannot label a child with CVID until you have systematically ruled out every other cause of hypogammaglobulinaemia, both primary and secondary. The reason is simple: CVID is a heterogeneous "wastebasket" diagnosis, and many conditions that were once called CVID have since been reclassified as distinct monogenic disorders (e.g., CTLA-4 haploinsufficiency, LRBA deficiency, activated PI3Kδ syndrome). The expanding genetic landscape means the differential is ever-growing.

Let's work through this systematically, from first principles. A child presents with recurrent infections ± autoimmunity ± lymphoproliferation and is found to have low IgG ± low IgA/IgM. What else could this be?

The differential of CVID can be organised into three tiers:

Secondary (acquired) causes of hypogammaglobulinaemia — must be excluded first
Other primary immunodeficiencies — those that mimic CVID clinically or serologically
Non-immunological mimics — conditions that present with recurrent infections but have a different underlying mechanism

Differentials: exclude anatomical and functional disorders. May also present with non-infectious symptoms. ^[7]

Exclude secondary immunodeficiency: Diabetes, HIV, protein-losing states, CKD, malignancy, immunosuppression, drugs, structural defects ^[7]

These are acquired conditions that lower immunoglobulin levels. They must be ruled out before diagnosing any primary antibody deficiency.

Secondary Cause	Mechanism	Key Distinguishing Features from CVID	How to Exclude
HIV infection ^[7]	CD4+ T-cell depletion → loss of T-cell help → impaired B-cell function → hypogammaglobulinaemia (though hypergammaglobulinaemia is more common in HIV due to polyclonal B-cell activation)	Risk factors (vertical transmission in paediatrics); opportunistic infections (PJP, CMV, oral thrush); CD4 count low	HIV status (Antigen or PCR) ^[7]; in infants < 18 months, use HIV DNA PCR (maternal IgG antibodies cross placenta → serology unreliable)
Drug-induced ^[7]	Rituximab (anti-CD20) → B-cell depletion → prolonged hypogammaglobulinaemia; Anti-epileptics (carbamazepine, phenytoin, valproate) → mechanism unclear, possibly impaired Ig synthesis; Systemic corticosteroids → lymphocyte apoptosis + reduced Ig production	Temporal relationship with drug initiation; recovery after drug cessation (though rituximab effects can last > 12 months)	Thorough drug history
Protein-losing states ^[7]	Nephrotic syndrome: massive urinary protein loss including immunoglobulins (IgG lost > IgM because IgG is smaller); Protein-losing enteropathy (PLE): intestinal loss of Ig; Burns: skin barrier loss → protein exudation	Low albumin accompanies the low Ig; oedema; proteinuria (nephrotic); Alpha-1-antitrypsin in stool (PLE)	Urinalysis, serum albumin, stool alpha-1-antitrypsin
Malignancy ^[7]	Lymphoma/CLL/ALL → infiltrate bone marrow → suppress normal B-cell function; myeloma produces monoclonal Ig but suppresses normal polyclonal Ig	B symptoms (fever, night sweats, weight loss); lymphadenopathy; abnormal blast cells on blood film; monoclonal band on electrophoresis	Serum and urine electrophoresis ^[7]; CBC + blood film; bone marrow aspirate if indicated
CKD ^[7]	Uraemic immune dysfunction → impaired lymphocyte function + increased catabolism of immunoglobulins	Elevated creatinine/urea; oliguria; other features of CKD	Liver and renal function tests ^[7]
Diabetes ^[7]	Hyperglycaemia → impaired neutrophil and lymphocyte function; not classic hypogammaglobulinaemia but increased infection susceptibility	Polyuria, polydipsia, weight loss; HbA1c elevated	Glucose, HbA1c
Post-HSCT / post-transplant	Immunosuppressive medications + graft-vs-host disease → impaired B-cell reconstitution	History of transplant is obvious	Clinical history

Exam Pearl — Always Exclude Secondary Causes First

The single most common mistake in approaching hypogammaglobulinaemia is jumping to a primary immunodeficiency diagnosis without excluding secondary causes. The initial evaluation must exclude secondary immunodeficiency ^[7]. In Hong Kong paediatric practice, drug-induced (especially if the child has been on anti-epileptics or has received rituximab for autoimmune disease) and protein-losing states (nephrotic syndrome is common in children) are the most important secondary causes to exclude.

4. Other Primary Immunodeficiencies That Mimic CVID

Condition	Gene / Inheritance	Key Immunological Difference from CVID	Key Clinical Difference	How to Differentiate
X-linked agammaglobulinaemia (XLA) ^[4]	BTK (XLR) ^[4]	↓B cells (near absent), pan-hypogammaglobulinaemia ^[4]; B cells are ABSENT because BTK is essential for all stages of B-cell development	Males only; presents earlier (after 4–6 months); absent tonsils ^[4]; no lymphoproliferation or autoimmunity (no B cells to cause it)	B-cell enumeration by flow cytometry (CD19+ cells absent in XLA, present in CVID); BTK protein/gene analysis
Hyper-IgM syndrome (HIGM) ^[4]	CD40L / CD40 / AID / UNG; Type 1 is XLR (CD40L mutation) ^[3]	↑IgM, ↓IgG/A/E ^[4] — this is the critical distinguishing pattern; failure to switch IgM to IgG/A ^[4]	Presents with similar sinopulmonary infections BUT also susceptible to opportunistic infections (PJP, Cryptosporidium) because CD40L deficiency also impairs T-cell-macrophage interaction; Cryptosporidium → sclerosing cholangitis is a classic association	IgM level (elevated in HIGM vs. low/normal in CVID); induced expression of CD40L (absent in HIGM Type 1, normal in CVID case ^[6])
Selective IgA deficiency ^[4]	Unknown / polygenic	IgA low (< 0.07 g/L), IgG and IgM NORMAL	Most common PID ^[4]; usually asymptomatic ^[4]; may occasionally present with recurrent mucosal infections or coeliac-like GI disease; risk of anaphylaxis to blood products containing IgA (anti-IgA antibodies)	IgG is normal (unlike CVID where IgG is always low); some patients progress to CVID over time
Transient hypogammaglobulinaemia of infancy (THI)	N/A (physiological delay)	Temporary low IgG in infants due to delayed maturation of Ig production after waning of maternal IgG; IgG normalises by age 2–4 years	Infants < 4 years; usually well despite mild infections; IgG rises spontaneously with age	Serial Ig measurements over time; CVID diagnosis requires age ≥ 4 years to exclude THI
Specific antibody deficiency (SAD)	Unknown	Normal total IgG, IgA, IgM, but impaired response to polysaccharide vaccine antigens (e.g., pneumococcal)	Recurrent sinopulmonary infections despite normal Ig levels	Post-vaccination antibody titres (especially anti-pneumococcal serotype-specific IgG)

High Yield — XLA vs CVID vs HIGM

This is the most commonly tested comparison in paediatric immunodeficiency:

XLA: No B cells → no tonsils → pan-hypo-Ig → males only → present at 4–6 months
CVID: B cells present → tonsils/LN present (may be enlarged!) → ↓↓↓IgG, ↓IgA/E → M=F → present later (> 4 years)
HIGM: B cells present → ↑IgM, ↓IgG/A/E → susceptible to PJP/Cryptosporidium → check CD40L expression

These are important differentials because some monogenic CIDs can present with a "CVID-like" phenotype initially before the full clinical picture emerges.

Condition	Gene / Inheritance	Why It Mimics CVID	How to Differentiate
SCID ^[4]	Multiple (IL2RG XLR is most common)	Low immunoglobulins; recurrent infections	Fatal without treatment; presents with FTT, recurrent severe infections ^[4]; ↓ALC (absolute lymphocyte count), absent thymus shadow on CXR ^[4]; presents much earlier (first few months of life) and is much more severe (opportunistic infections — PJP, disseminated BCG, oral thrush); commonly cause severe ± unusual viral and fungal infections ^[4]
Activated PI3Kδ syndrome (APDS) ^[5]	PIK3CD (AD, gain-of-function) ^[5]	Hypogammaglobulinaemia + lymphoproliferation → initially labelled as CVID	Severe bacterial infections, lymphadenopathy, lymphoproliferation, lymphoma; reduced memory B cells and increased transitional B cells; EBV+/CMV viraemia, autoimmunity ^[5]; more severe herpesvirus susceptibility than typical CVID; genetic testing (PIK3CD/PIK3R1)
CTLA-4 haploinsufficiency	CTLA4 (AD)	Hypogammaglobulinaemia + autoimmune cytopenias + lymphocytic infiltration of organs → "CVID with autoimmunity"	Prominent lymphocytic infiltration of lungs, GI, brain; granulomatous-lymphocytic interstitial lung disease (GLILD); responds to abatacept (CTLA-4-Ig fusion protein); genetic testing
LRBA deficiency	LRBA (AR)	Phenocopies CTLA-4 haploinsufficiency (LRBA protein traffics CTLA-4 to cell surface)	Very similar to CTLA-4 deficiency; autoimmune enteropathy, cytopenias, lymphocytic interstitial pneumonitis; responds to abatacept; genetic testing
Wiskott-Aldrich syndrome (WAS) ^[4]	WAS (XLR)	Low IgM; recurrent infections	Triad: immunodeficiency + thrombocytopenia (micro-thrombocytes!) + eczema ^[4]; WAS thrombocytopenia has characteristically small platelets (unlike ITP where platelets are large); males only
DiGeorge syndrome ^[4]	22q11.2 deletion (AD/de novo)	T-cell deficiency → secondary antibody deficiency (poor T-cell help)	Triad: conotruncal cardiac anomalies + hypoplastic thymus + hypoplastic parathyroid (hypocalcaemia) ^[4]; characteristic facies; presents in neonatal period with cardiac defects or neonatal hypocalcaemic seizures

Critical Distinction — CVID vs SCID

Do NOT confuse CVID with SCID. SCID is an emergency — these infants are profoundly immunodeficient from birth, develop overwhelming infections (severe bronchiolitis, oral thrush, PJP, disseminated CMV ^[4]), and die without HSCT. CVID is milder, presents later, and is compatible with survival (though with complications). The key lab difference: SCID has ↓ALC (absolute lymphocyte count) ^[4] and absent T cells, while CVID typically has normal or near-normal ALC and present (though dysfunctional) B cells.

These don't typically present with hypogammaglobulinaemia, but they enter the differential when a child has recurrent infections in general.

Condition	Why It's in the Differential	How to Differentiate from CVID
Chronic granulomatous disease (CGD) ^[4]^[3]	Recurrent infections + granuloma formation + hepatosplenomegaly → can overlap with CVID's granulomatous phenotype	Phagocytes fail to produce superoxide → inability to destroy catalase-positive organisms ^[4]; recurrent deep abscesses (skin, liver, perianal), catalase-positive organisms (S. aureus, Aspergillus, Serratia, Burkholderia, Nocardia); BCG dissemination ^[4]; IgG is normal or high (not low!); diagnosis by dihydrorhodamine (DHR) flow cytometry or nitroblue tetrazolium (NBT) test; neutrophil respiratory burst function normal in CVID case ^[6]
Leukocyte adhesion deficiency (LAD) ^[4]	Recurrent infections; enters differential of recurrent bacterial infections in infants	↑neutrophil count (trapped in vessels), poor wound healing, absent pus, delayed umbilical cord separation, omphalitis ^[4]; Ig levels normal; flow cytometry for CD18
Complement deficiency ^[4]	Recurrent infections with encapsulated bacteria (same pathogen pattern as antibody deficiency!)	Terminal complement (C5–C9) deficiency → recurrent Neisseria; early complement (C1–C4) → SLE-like illness; C3/C4 levels are part of first-line investigations ^[7]; Ig levels normal

Condition	Key Clinical Clue That Distinguishes from CVID
Hyper-IgE syndrome (HIES) ^[4]	Pneumatocele, mucocutaneous candidiasis, retained primary teeth, minimal-trauma fractures, scoliosis; high IgE; less allergy/anaphylaxis than expected for IgE level ^[4]
X-linked lymphoproliferative disease (Duncan disease) ^[4]	Abnormal response to EBV → either succumb to initial infection or develop secondary lymphoma ^[4]
Ataxia-telangiectasia ^[4]	Cerebellar ataxia, developmental delay, ↑risk of lymphoma ^[4]; oculocutaneous telangiectasias; elevated AFP; low IgA

Differentials: exclude anatomical and functional disorders ^[7]

These conditions cause recurrent infections through structural or functional problems rather than immune deficiency. Immunoglobulins are normal.

Condition	Mechanism	How to Differentiate
Cystic fibrosis (CF)	AR mutation in CFTR → thick mucus → impaired mucociliary clearance → recurrent sinopulmonary infections, bronchiectasis; also causes pancreatic insufficiency (steatorrhoea), male infertility ^[9]	Sweat chloride test (gold standard); newborn screening (IRT); genetic testing; steatorrhoea + failure to thrive + recurrent chest infections in a non-immune-deficient child → think CF
Primary ciliary dyskinesia (PCD)	Dynein mutation (AR) → immotile cilia → impaired mucociliary clearance → sinusitis, otitis media, bronchiectasis; Kartagener syndrome = PCD + situs inversus ^[9]	Nasal nitric oxide (low); ciliary biopsy with electron microscopy; genetic panel; history of neonatal respiratory distress
Anatomical defects	Cleft palate → recurrent otitis media; tracheo-oesophageal fistula → recurrent aspiration pneumonia; congenital lobar emphysema → recurrent focal infections	Clinical examination; imaging (barium swallow, CT)
Gastro-oesophageal reflux / aspiration	Recurrent micro-aspiration → recurrent lower respiratory infections	History of feeds-related coughing/choking; pH study; barium swallow
Allergic disease / asthma	Recurrent "wheeze + cough" episodes misdiagnosed as recurrent chest infections	Spirometry; bronchodilator reversibility; allergy testing; no true documented infections on culture
Foreign body aspiration	Unilateral recurrent pneumonia (same lobe) due to partial airway obstruction	Rigid bronchoscopy; inspiratory/expiratory CXR or CT
Adenoidal / tonsillar hypertrophy	Eustachian tube obstruction → recurrent otitis media	Lateral neck X-ray; ENT assessment

Hong Kong Context

In Hong Kong, tuberculosis is still endemic and must always be considered in a child with recurrent or prolonged respiratory infections, lymphadenopathy, or failure to thrive. TB is NOT a primary immunodeficiency but can mimic one. Conversely, children with primary immunodeficiency (especially CGD, SCID, MSMD) are at high risk of BCG dissemination ^[4] — a red flag for underlying immune deficiency in a vaccinated infant.

The age at which infections begin is a powerful discriminator:

Age of Onset	Most Likely PID Category	Key Differentials
0–3 months	T-cell / combined defects (SCID, DiGeorge); also innate defects (LAD, CGD)	Maternal IgG still protective → antibody deficiencies unlikely at this age
4–6 months ^[4]	Antibody deficiencies begin to manifest as maternal IgG wanes	XLA, HIGM, SCID (if not yet diagnosed)
6 months – 4 years	All antibody deficiencies + THI	THI is the main differential in this age group; cannot diagnose CVID until ≥ 4 years
> 4 years	CVID (by definition diagnosed ≥ 4 years)	Also consider APDS, CTLA-4 haploinsufficiency, LRBA deficiency
Adolescence / young adulthood	CVID (second peak); also consider secondary causes (HIV, drugs)	Always re-evaluate for secondary causes in adolescents

The following investigations help navigate the differential systematically. This is summarised from the first-line investigations framework ^[7] and the immunology workup approach ^[5]^[6]:

Investigation	What It Tells You	Differential Narrowing
CBC and differentials ^[7]	ALC, neutrophil count, platelet count + size	ALC < 2,500/µL in infants → think SCID; ↑neutrophils → LAD; thrombocytopenia with small platelets → WAS
Immunoglobulin profile (IgG, IgA, IgM, IgE) ^[7]	Pattern of Ig deficiency	Pan-low → XLA or SCID; ↓IgG/A with ↑IgM → HIGM; ↓IgA only → selective IgA deficiency; ↓↓↓IgG + ↓IgA/IgM → CVID; ↑IgE → HIES or atopy
B-cell enumeration (CD19+ by flow cytometry)	Are B cells present?	Absent B cells → XLA ^[4]^[5]; B cells present → CVID, HIGM, or other
B-cell subsets (switched memory B cells) ^[6]	Class-switching capacity	Switched memory B cells absent → CVID (poor prognosis phenotype) ^[6]
Vaccine responses	Functional antibody production	Tetanus, HAV, HBV antibodies negative despite vaccination → impaired vaccine responses → supports CVID ^[6]
CD40L expression ^[6]	T-cell function for class switching	Normal in CVID; absent in HIGM Type 1 ^[6]
Neutrophil respiratory burst (DHR) ^[6]	Phagocyte oxidative killing	Normal in CVID; absent in CGD ^[6]
HIV status ^[7]	Exclude HIV	Must exclude before diagnosing any PID
Genetic testing (NGS panel)	Identify monogenic cause	May reclassify "CVID" as APDS, CTLA-4 deficiency, LRBA deficiency, etc.

Feature	CVID	XLA	HIGM	SCID	APDS	CGD
Age of onset	> 4 years	4–6 months	4–6 months	0–3 months	Childhood	Infancy
Sex	M = F	Males only	Males (Type 1)	Variable	M = F	Males (XL form)
B cells	Present	Absent	Present	Variable	Present	Normal
IgG	↓↓↓	↓↓↓	↓	↓	↓	Normal/↑
IgM	↓/normal	↓↓↓	↑↑	↓	↓/normal	Normal
IgA	↓	↓↓↓	↓	↓	↓	Normal
T cells	Usually normal	Normal	Normal (Type 1)	Absent/↓↓	↓ memory	Normal
ALC	Normal/low-normal	Normal	Normal	↓↓↓	Low	Normal
Tonsils	Present	Absent	Present	Variable	Present	Present
Autoimmunity	~25%	Rare	Less common	No	Common	Uncommon
Lymphoproliferation	~33%	No	No	No	Yes	Granulomas
Key pathogens	Encapsulated bacteria, Giardia	Encapsulated bacteria, Enterovirus	PJP, Cryptosporidium	All (PJP, CMV, BCG)	Bacteria, EBV, CMV	S. aureus, Aspergillus, BCG
Key test	Ig profile + vaccine response + B-cell subsets	B-cell count + BTK	CD40L expression + IgM	ALC + T-cell subsets + TREC	Genetic testing (PIK3CD)	DHR / NBT

High Yield Summary — Differential Diagnosis of CVID

Always exclude secondary causes first: HIV, drugs (rituximab, anti-epileptics), protein-losing states (nephrotic syndrome, PLE), malignancy, CKD.
Key primary immunodeficiency differentials:
- XLA: No B cells, no tonsils, males only, BTK mutation, presents at 4–6 months
- HIGM: ↑IgM, ↓IgG/A/E, CD40L deficiency (Type 1), PJP + Cryptosporidium susceptibility
- SCID: Very low ALC, absent thymus, presents in first months of life, fatal without HSCT
- APDS: CVID-like but with more severe lymphoproliferation, herpesvirus susceptibility, PIK3CD GOF
- CTLA-4 / LRBA deficiency: CVID with prominent autoimmunity and organ infiltration
Non-immunological mimics: CF (sweat test), PCD (nasal NO, ciliary biopsy), anatomical defects, GOR/aspiration, allergic disease.
Age is your friend: SCID → 0–3 months; XLA/HIGM → 4–6 months; CVID → ≥ 4 years.
Confirm CVID with: low IgG (+ low IgA ± low IgM), impaired vaccine responses, age ≥ 4, B cells present, exclude all above.

Active Recall - Differential Diagnosis of CVID

References

^[3] Senior notes: Jerry's immunodeficiencies.pdf (CVID, HIGM, and CGD sections) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p410–411 — Primary Immunodeficiency examples) ^[5] Lecture slides: Investigations of Imm Disorders 2025.pdf (p21 — Predominantly Antibody Deficiencies classification, APDS) ^[6] Lecture slides: Investigations of Imm Disorders 2025.pdf (p14 — CVID case lab results including CD40L, DHR, switched memory B cells) ^[7] GC Lecture slides: GC 096. Why do I always get sick.pdf (p19, p21 — General principles, initial evaluation, first-line investigations) ^[9] Senior notes: Maksim Medicine Notes.pdf (p303 — Bronchiectasis aetiology including CF, PCD, CVID)

Diagnostic Criteria, Algorithm, and Investigations for CVID in Paediatrics

1. Diagnostic Criteria

CVID is a clinical diagnosis of exclusion — there is no single pathognomonic test. The diagnosis rests on demonstrating significant hypogammaglobulinaemia with impaired functional antibody responses after systematically excluding every other cause. Two major consensus frameworks exist; the ESID 2019 criteria are the most widely used.

All of the following must be met:

Criterion	Detail	Rationale (Why?)
1. Marked decrease in IgG	At least 2 standard deviations below the age-matched mean, measured on ≥ 2 occasions, ≥ 3 weeks apart	Why twice? To exclude transient drops (e.g., during acute infection, lab error). Why age-matched? Because normal IgG varies dramatically with age — a 1-year-old's normal IgG is much lower than a teenager's. Paediatric age-specific reference ranges must be used.
2. Low IgA and/or low IgM	At least one of the other isotypes also reduced	CVID characteristically has ↓↓↓IgG, ↓IgA/E ^[4]; isolated IgG deficiency with normal IgA/IgM is more suggestive of specific antibody deficiency or secondary causes.
3. Impaired vaccine responses	Poor response to protein antigens (e.g., tetanus, diphtheria) AND/OR polysaccharide antigens (e.g., pneumococcal serotypes)	This is the functional test — it proves the B cells cannot mount an effective antibody response. Tetanus, HAV, HBV antibodies neg despite vaccination in the lecture case ^[6]. Without this criterion, you cannot distinguish CVID from a child who simply has low baseline Ig but can still respond to challenges.
4. Exclusion of other defined causes	No other primary immunodeficiency (XLA, HIGM, SCID, etc.) or secondary cause (drugs, HIV, protein loss, malignancy)	CVID remains a diagnosis of exclusion. Exclude secondary immunodeficiency: Diabetes, HIV, protein-losing states, CKD, malignancy, immunosuppression, drugs, structural defects ^[7].
5. Age ≥ 4 years at diagnosis	Cannot be diagnosed before age 4	To exclude transient hypogammaglobulinaemia of infancy (THI), which is a physiological delay in immunoglobulin maturation that resolves spontaneously. Before age 4, the diagnosis should be "probable" or "possible" CVID, with serial monitoring.

Paediatric-Specific: Age-Matched Immunoglobulin Reference Ranges

Normal immunoglobulin levels vary dramatically with age. At birth, IgG is high (maternal transfer), drops to a nadir at 3–6 months, then gradually rises. IgM is the first isotype produced by the infant (detectable from birth). IgA is very low at birth and rises slowly over years. Always compare to age-matched reference ranges — a "low" IgG in a 6-month-old may be physiological, whereas the same level in a 10-year-old is pathological.

Approximate paediatric IgG reference ranges (vary by lab):

Newborn: 7.0–13.0 g/L (maternal)
3–6 months: 2.0–6.0 g/L (nadir)
1 year: 3.0–10.0 g/L
5 years: 5.0–13.0 g/L
10–16 years: 6.0–16.0 g/L

Very similar to ESID, but includes additional nuance:

IgG below the age-specific 5th centile (rather than 2 SD)
Emphasises that at least one of the following must also be present: recurrent infections, autoimmune manifestations, granulomatous disease, unexplained polyclonal lymphoproliferation, or affected family member
Still requires exclusion of secondary causes and age ≥ 4 years

To diagnose CVID in a child, you need ALL of:

Low IgG (below age-matched reference, confirmed on 2 samples ≥ 3 weeks apart)

Low IgA and/or IgM

Impaired vaccine responses

Age ≥ 4 years

Exclusion of other causes (primary and secondary)

Exam Pearl — Why Vaccine Responses Are Essential

A common mistake is diagnosing CVID based on low immunoglobulins alone. You MUST demonstrate impaired vaccine responses — this is the functional proof that the B cells cannot produce effective antibodies. Without this, the child might have secondary hypogammaglobulinaemia (e.g., from protein loss) with functionally normal B cells. Tetanus, HAV, HBV antibodies neg despite vaccination ^[6] is the classic finding.

The approach to diagnosing CVID follows a structured pathway: Clinical suspicion → Exclude secondary causes → First-line investigations → Immunological workup → Functional testing → Genetic testing → Classification and monitoring.

3. Investigation Modalities — Detailed Guide

These are ordered when any child is suspected of having a primary immunodeficiency. They are not CVID-specific but help identify the category of immune defect and exclude secondary causes.

First-line investigations: ^[7]

CBC and differentials

Absolute lymphocyte count

Liver and renal function tests

Protein and globulin level

Acute phase reactants (ESR/CRP) — ↓ESR if low globulin/fibrinogen

Immunoglobulin profile (incl IgE)

Serum and urine electrophoresis

C3 / C4

ANA ± autoimmune serologies

HIV status (Antigen or PCR)

CXR / CT Thorax / Lung function ^[7]

Investigation	Expected Findings in CVID	Why This Test?	Key Interpretive Points
CBC + differential	Usually normal; may show mild lymphopenia, anaemia (AIHA), thrombocytopenia (ITP), or neutropenia (autoimmune)	Screens for cytopenias (autoimmune complications); helps exclude leukaemia (blasts on film), SCID (very low ALC)	Lowish lymphocyte count (0.85–0.96 × 10⁹/L) ^[6] — in the lecture case, ALC was low-normal. In SCID, ALC is markedly low (< 2,500/µL in infants). Paediatric ALC normal values are higher than adults (infants: 4,000–10,000; school-age: 1,500–6,500).
Absolute lymphocyte count (ALC) ^[7]	Normal or low-normal in CVID	If ALC is very low → think SCID or combined immunodeficiency, NOT pure antibody deficiency	Always use age-specific normal ranges — infants normally have higher lymphocyte counts than older children or adults
Protein and globulin level ^[7]	Low total protein, low globulin	Serum globulin is a rough surrogate for immunoglobulins (which constitute most of the gamma-globulin fraction). A low globulin on routine biochemistry should prompt formal immunoglobulin quantification.	A quick clue on routine bloods: "protein 55, albumin 40" means globulin gap = 15 (normal ~25–35) → suggests hypogammaglobulinaemia
ESR/CRP ^[7]	↓ESR if low globulin/fibrinogen ^[7]; CRP may be elevated during acute infection	ESR depends on rouleaux formation, which requires immunoglobulins (especially IgM). In CVID, low Ig → paradoxically low ESR even during infection. CRP is liver-derived and not affected by Ig levels, so it remains a reliable infection marker.	A discordance of low ESR + elevated CRP in a febrile child should strongly raise suspicion for hypogammaglobulinaemia
Immunoglobulin profile (IgG, IgA, IgM, IgE) ^[7]	↓↓↓IgG, ↓IgA/E ^[4]; IgM may be low or normal	The cornerstone investigation. Must compare to age-specific reference ranges.	In CVID: IgG is always low. IgA is usually low. IgM can be low or normal. IgE is often low. Contrast with Hyper-IgM (↑IgM, ↓IgG/A/E ^[4]) and XLA (pan-low including IgM).
Serum and urine electrophoresis ^[7]	Absent or markedly reduced gamma-globulin band on serum protein electrophoresis (SPEP). No monoclonal band.	Excludes myeloma (monoclonal spike) in adults; in paediatrics, excludes rare lymphoproliferative disorders. Confirms polyclonal hypogammaglobulinaemia.	A "flat gamma region" on SPEP = hypogammaglobulinaemia. A monoclonal spike would suggest lymphoproliferative disease, not CVID.
C3 / C4 ^[7]	Usually normal in CVID	Excludes complement deficiency (which also causes recurrent encapsulated bacterial infections). Low C3 ± C4 → complement pathway defects.	C4 may be consumed in SLE or cryoglobulinaemia. C3/C4 normal in CVID rules out complement pathway as the main problem.
ANA ± autoimmune serologies ^[7]	May be positive (autoimmune complications are common in CVID)	Screens for associated autoimmune conditions (SLE, AIHA, ITP)	ANA positivity in a child with hypogammaglobulinaemia + cytopenias supports the autoimmune phenotype of CVID
HIV status (Antigen or PCR) ^[7]	Must be negative to diagnose CVID	HIV neg ^[6] — mandatory exclusion. In paediatrics, note: for infants < 18 months, use HIV DNA PCR (not antibody testing, since maternal anti-HIV IgG crosses the placenta and can give false positive serology).	In adolescents, consider risk factors and ensure confidential testing with appropriate pre- and post-test counselling
CXR / CT Thorax / Lung function ^[7]	CXR may show bronchiectasis ^[1], lymphadenopathy, or interstitial lung disease. CT thorax is more sensitive for bronchiectasis and GLILD. Lung function (spirometry) may show obstructive or restrictive pattern.	Establishes baseline lung status; detects established end-organ damage; screens for granulomatous-lymphocytic interstitial lung disease (GLILD) ^[1]	In SCID: absent thymus shadow on CXR ^[4] — this is an important differentiating finding. In CVID, thymus is present.

High Yield — The Low Globulin Clue

On routine biochemistry, the "albumin-globulin gap" is a quick screening tool. Total protein − albumin = globulin. If globulin is low (< 20 g/L in older children), the main cause is hypogammaglobulinaemia. This often gets overlooked on routine bloods but should trigger formal Ig quantification.

Once first-line tests suggest antibody deficiency (low IgG ± IgA/IgM), the next step is a focused immunological assessment to confirm CVID and exclude other PIDs.

Investigation	Expected Findings in CVID	What It Excludes	Key Interpretive Points
B-cell enumeration (CD19+ by flow cytometry)	B cells present (> 1% of lymphocytes, usually 5–15%)	XLA: absent B cells (CD19+ < 1%) ^[4]^[5] — this is the single most important test to differentiate CVID from XLA	B lymphocyte (CD19+) enumeration → Bc absent → XLA; Bc > 1% → CVID phenotype ^[5]
B-cell subsets ^[6]	Switched memory B cells (CD27+IgD−IgM−) absent ^[6]	Helps prognosticate and classify CVID (EUROclass: smB+ vs smB−)	Switched memory B cell absent → more prone to recurrent respiratory infections and development of bronchiectasis ^[6]. Expanded CD21low B cells and transitional B cells may indicate immune dysregulation.
Vaccine responses (functional antibody assessment)	Tetanus, HAV, HBV antibodies neg despite vaccination ^[6]	Excludes specific antibody deficiency (SAD) where total Ig is normal but polysaccharide responses are impaired; also excludes THI (where vaccine responses are usually intact)	Check both protein antigen responses (anti-tetanus, anti-diphtheria) AND polysaccharide antigen responses (anti-pneumococcal serotypes). In children < 2 years, polysaccharide responses are physiologically poor → use conjugate vaccine responses instead.
Isohaemagglutinins ^[6]	Isohaemagglutinin positive in the lecture case ^[6] — but may be absent in some CVID patients	Isohaemagglutinins (anti-A or anti-B natural antibodies, IgM class) test the ability to make T-independent antibodies. Their absence supports antibody deficiency but their presence does not exclude CVID.	In CVID, residual IgM production can maintain isohaemagglutinins. In XLA (no B cells at all), isohaemagglutinins are absent. Note: blood group AB patients naturally have no isohaemagglutinins → this test is uninformative in them.
Induced expression of CD40L ^[6]	Normal ^[6]	Excludes Hyper-IgM syndrome Type 1 (CD40L deficiency) — in HIGM Type 1, CD40L expression on activated T cells is absent	CD40L is expressed on activated CD4+ T cells. When T cells are stimulated in vitro (e.g., with PMA + ionomycin), normal T cells express CD40L. Absence → HIGM Type 1.
Lymphocyte proliferation ^[6]	Normal in CVID ^[6]	Excludes combined immunodeficiency — in CID/SCID, T-cell proliferative responses to mitogens (PHA, ConA) and antigens (tetanus, Candida) are impaired	If T-cell proliferation is impaired alongside hypogammaglobulinaemia → reclassify as combined immunodeficiency, not CVID
Neutrophil respiratory burst (DHR flow cytometry) ^[6]	Normal in CVID ^[6]	Excludes CGD — in CGD, phagocytes fail to produce reactive oxygen species; DHR reduction is low ^[3]	DHR flow cytometry has replaced the older nitroblue tetrazolium (NBT) test. The principle: add dihydrorhodamine to neutrophils → stimulate oxidative burst → DHR is oxidised to rhodamine (fluorescent) → measured by flow cytometry. In CGD: no fluorescence shift.
T-cell subsets (CD3, CD4, CD8)	Usually normal or mildly abnormal; may show reduced CD4, inverted CD4:CD8 ratio	Excludes SCID (severely reduced T cells); helps identify combined features	Subset % normal in the lecture case ^[6], but some CVID patients have T-cell abnormalities which contribute to disease severity

Step-by-Step Logic of the CVID Workup

Think of it as a funnel:

Low Ig → Is this real? (Confirm on two occasions)
B cells present? → Yes = could be CVID. No = think XLA.
CD40L normal? → Yes = not HIGM Type 1.
T cells normal? → Yes = not combined immunodeficiency.
Vaccine responses impaired? → Yes = functional antibody deficiency confirmed.
DHR normal? → Yes = not CGD.
Age ≥ 4? → Yes = can diagnose CVID.
All secondary causes excluded? → Yes = CVID confirmed.

Genetic tests ^[6] are pursued after a clinical diagnosis of CVID is established, for several important reasons:

May identify a monogenic cause that reclassifies the patient (e.g., CTLA-4 haploinsufficiency, LRBA deficiency, APDS) → implications for targeted therapy
Determines inheritance pattern → critical for genetic counselling of the family
Identifies siblings/family members at risk

Genetic Test	Findings in CVID	Interpretation
Targeted gene panel (TACI, ICOS, CD19, BAFF-R)	TACI, BAFF-R, ICOS normal (2× in 2 labs) in the lecture case ^[6]	Mutations in these four genes together account for only 10–15% of CVID cases ^[1]^[3]; a negative result does NOT exclude CVID
Next-generation sequencing (NGS) — PID gene panel or whole exome	NGS: BLK variant identified, heterozygous, limited evidence of clinical relevance ^[6]	Many variants of uncertain significance (VUS) are found; requires careful interpretation with clinical and functional correlation. NGS is increasingly identifying "CVID-like" monogenic conditions (CTLA-4, LRBA, NFKB1, NFKB2, PIK3CD/PIK3R1, IKAROS) ^[10]
Sanger sequencing	Used to confirm variants identified by NGS	Confirmed by Sanger sequencing ^[6] — gold standard for variant verification

Mutations have been described in four genes: ICOS, CD19, BAFF-R and TNFRSF13B [TACI], together associated with 10–15% of CVID cases ^[1]

More recently identified monogenic CVID-like conditions (from the expanding IUIS classification) ^[10]:

Gene	Inheritance	Key Distinguishing Features
NFKB1 ^[10]	AD	Recurrent sinopulmonary infections, COPD, EBV proliferation, autoimmune cytopenias, alopecia, autoimmune thyroiditis
NFKB2 ^[10]	AD	Recurrent sinopulmonary infections, alopecia, endocrinopathies (central adrenal insufficiency)
IKAROS (IKZF1) ^[10]	AD	Recurrent sinopulmonary infections; increased risk of ALL, autoimmunity; decreased pro-B cells
PIK3CD (APDS) ^[5]	AD (GOF)	Severe bacterial infections, lymphoproliferation, lymphoma, EBV+/CMV viraemia
CTLA-4	AD	Prominent autoimmunity, lymphocytic organ infiltration, responds to abatacept
LRBA	AR	Phenocopies CTLA-4 deficiency; responds to abatacept

High Yield — When Genetic Testing Reclassifies CVID

In the modern era, what was once labelled "CVID" is increasingly being re-diagnosed as distinct monogenic entities through NGS. This matters clinically because:

CTLA-4 haploinsufficiency / LRBA deficiency → respond to abatacept (CTLA-4-Ig)
APDS → responds to PI3K inhibitors (leniolisib, approved 2023)
NFKB1/2 deficiency → specific prognostic and screening implications
LRBA deficiency → may benefit from HSCT in severe cases

Always pursue genetic testing — it changes management!

Once CVID is diagnosed, establish baseline end-organ status so that progressive damage can be detected early:

Investigation	Purpose	Key Findings
HRCT thorax	Baseline lung assessment; detect bronchiectasis, GLILD	Bronchiectasis ^[1] — cylindrical dilatation of bronchi (tram-track sign, signet ring sign); ground-glass opacities and nodules suggest GLILD
Pulmonary function tests (spirometry ± DLCO)	Quantify lung function impairment; serial monitoring	Obstructive pattern (bronchiectasis) or restrictive pattern (GLILD); reduced DLCO in interstitial disease. In children > 6 years who can perform reliable spirometry. Younger children may use oscillometry.
Abdominal ultrasound	Assess for splenomegaly, hepatomegaly, lymphadenopathy	Splenomegaly seen in ~1/3 with lymphoproliferative phenotype ^[1]; hepatomegaly if granulomatous hepatitis
Complete blood count (serial)	Monitor for autoimmune cytopenias	ITP and AIHA in up to 25% ^[1]; Evans syndrome (ITP + AIHA)
LFT	Hepatic granulomatous disease; nodular regenerative hyperplasia	Elevated ALP, GGT suggest granulomatous hepatitis; elevated transaminases suggest hepatitis
Direct antiglobulin test (DAT / Coombs)	Screen for AIHA	Positive DAT (IgG-mediated warm AIHA or C3d-mediated cold AIHA) supports autoimmune haemolysis
Reticulocyte count, LDH, haptoglobin, bilirubin	Haemolysis workup if anaemia present	Elevated reticulocytes + elevated LDH + low haptoglobin + elevated unconjugated bilirubin = haemolysis
Stool studies	Chronic diarrhoea workup	Giardia antigen/PCR (most common GI pathogen in antibody deficiency); stool cultures; faecal calprotectin (IBD-like inflammation)
Endoscopy ± biopsy (upper and lower GI)	If chronic GI symptoms	Nodular lymphoid hyperplasia of the small bowel ^[1]; villous atrophy (sprue-like); IBD-like colitis; exclude GI lymphoma
Growth and nutritional assessment	Paediatric-specific — essential	Serial weight, height/length, head circumference on appropriate growth charts; nutritional bloods (iron, zinc, folate, B12, fat-soluble vitamins A/D/E/K); bone density if malabsorption suspected
Developmental assessment	Paediatric-specific	Chronic illness may impair developmental milestones — serial assessment with referral to developmental paediatrician if concerns

4. Special Considerations in Paediatric Diagnosis

This deserves re-emphasis because it is the most common source of diagnostic error in paediatric immunology:

Age	IgG (g/L)	IgA (g/L)	IgM (g/L)	Key Point
Cord blood	6.0–16.0	0.01–0.05	0.05–0.30	IgG is entirely maternal (transplacental); IgA and IgM are infant-derived
1–3 months	2.5–7.5	0.01–0.07	0.15–0.70	Maternal IgG waning; infant's own IgG not yet significant
3–6 months	1.8–6.0	0.02–0.15	0.20–1.00	Physiological nadir — lowest point of IgG before infant production catches up
1 year	3.0–10.0	0.10–0.60	0.40–1.80	Infant IgG production established but still lower than older children
5 years	5.0–13.0	0.30–1.50	0.50–2.00	Approaching adult levels
10–16 years	6.0–16.0	0.50–2.50	0.50–2.00	Adult-like

Protein antigen responses (tetanus, diphtheria): Can be assessed at any age after vaccination
Polysaccharide antigen responses (unconjugated pneumococcal vaccine — PPSV23): Physiologically poor in children < 2 years (immature marginal zone B cells) → cannot reliably assess polysaccharide responses until age 2
Use conjugate vaccine responses (PCV13) in younger children instead
After vaccination, draw titres at 4–6 weeks
"Protective" anti-tetanus ≥ 0.1 IU/mL; anti-pneumococcal ≥ 1.3 µg/mL per serotype (varies by lab)
In CVID: typically poor or absent responses to both protein and polysaccharide antigens

Not as rare as previously thought — ever-expanding list! Many patients remain undiagnosed or present later in life. High index of suspicion for early diagnosis and intervention. ^[7]

Refer when:

IgG confirmed low on two occasions
Recurrent severe or unusual infections with no anatomical explanation
Family history of immunodeficiency or consanguinity
Autoimmune cytopenias in a child (always check immunoglobulins!)
Unexplained bronchiectasis in a child

Result Pattern	Most Likely Diagnosis	Next Step
Low IgG/A/M, absent B cells	XLA	BTK gene testing
Low IgG/A, high IgM, B cells present	Hyper-IgM syndrome	CD40L expression; AID/UNG testing
Low IgG/A/M, very low ALC, absent thymus	SCID	T-cell subsets, TREC, urgent HSCT referral
Low IgG/A, IgM normal/low, B cells present, impaired vaccine responses, age ≥ 4	CVID	B-cell subsets, genetic panel, baseline organ assessment
Low IgG/A, IgM normal/low, B cells present, age < 4	Probable CVID vs. THI	Serial monitoring q6–12 months
Normal total Ig, impaired polysaccharide vaccine responses	Specific antibody deficiency	Trial of pneumococcal vaccination + re-check titres
Normal Ig, low ALC, abnormal T-cell function	Combined immunodeficiency (non-SCID)	Genetic testing (APDS, CTLA-4, etc.)

High Yield Summary — Diagnosis of CVID

ESID 2019 Criteria (all required):

IgG low (≥ 2 SD below age-matched mean, confirmed on 2 occasions ≥ 3 weeks apart)
Low IgA and/or IgM
Impaired vaccine responses (protein ± polysaccharide antigens)
Age ≥ 4 years
Exclusion of all other causes

Key investigations in order:

Tier 1: CBC, ALC, protein/globulin, ESR/CRP, Ig profile, SPEP, C3/C4, ANA, HIV, CXR
Tier 2: B-cell count (CD19+), B-cell subsets (switched memory B cells), vaccine responses, CD40L expression, lymphocyte proliferation, DHR
Tier 3: Genetic testing (TACI, ICOS, CD19, BAFF-R; NGS panel for expanding genes)
Tier 4: Baseline organ assessment (HRCT, PFTs, abdo USS, haemolysis screen, growth/nutrition)

Critical differentiating tests:

B cells absent → XLA, not CVID
CD40L absent → HIGM Type 1, not CVID
ALC very low / absent thymus → SCID, not CVID
DHR absent → CGD, not CVID

Paediatric pearls:

Always use age-matched Ig reference ranges
Cannot diagnose CVID before age 4 (exclude THI)
Polysaccharide vaccine responses unreliable before age 2 → use conjugate vaccine responses
ESR may be paradoxically low due to hypogammaglobulinaemia (↓rouleaux formation)

Active Recall - Diagnostic Criteria, Algorithm, and Investigations for CVID

References

^[1] Lecture slides: Investigations of Imm Disorders 2025.pdf (p15 — CVID section) ^[3] Senior notes: Jerry's immunodeficiencies.pdf (CVID, CGD, antibody deficiencies section) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p410 — Primary Immunodeficiency examples) ^[5] Lecture slides: Investigations of Imm Disorders 2025.pdf (p21 — Predominantly Antibody Deficiencies classification, APDS) ^[6] Lecture slides: Investigations of Imm Disorders 2025.pdf (p14 — CVID case lab results) ^[7] GC Lecture slides: GC 096. Why do I always get sick.pdf (p19, p21 — General principles, initial evaluation, first-line investigations) ^[10] Lecture slides: Investigations of Imm Disorders 2025.pdf (p21 — NFKB1, NFKB2, IKAROS, expanded gene list)

Management of CVID in Paediatrics

The management of CVID rests on four pillars. Understanding why each pillar exists connects directly to the underlying pathophysiology:

Pillar	Rationale (First Principles)
1. Immunoglobulin replacement	The core defect is defective Ig production ^[4] → replace what the body cannot make → prevents recurrent infections and end-organ damage
2. Prophylactic antibiotics	Even with Ig replacement, mucosal immunity (IgA) remains suboptimal → ongoing susceptibility to sinopulmonary colonisation → antibiotics reduce bacterial load and slow bronchiectasis progression
3. Treatment of complications	CVID causes autoimmune cytopenias in up to 25%, granulomatous disease in 8–22%, lymphoproliferation in ~1/3 ^[1] → each complication requires specific management
4. Surveillance and monitoring	Progressive end-organ damage (especially bronchiectasis, GLILD) and increased risk of gastrointestinal and lymphoid malignancies ^[1] → regular screening detects complications early

Treatment: Ig replacement, prophylactic antibiotics ^[7]

3. Pillar 1 — Immunoglobulin Replacement Therapy

This is the cornerstone of CVID management. The logic is straightforward: the child cannot make adequate IgG → supply it exogenously.

Feature	IVIG (Intravenous Immunoglobulin)	SCIG (Subcutaneous Immunoglobulin)
Route	Intravenous infusion	Subcutaneous injection (abdomen, thigh, upper arm)
Frequency	Every 3–4 weeks	Weekly or biweekly (some facilitated SCIG regimens allow monthly)
Setting	Hospital / day-care unit (requires monitoring during infusion)	Home-based — child/family trained to self-administer
Peak/trough kinetics	High post-infusion peak → gradual decline → trough just before next dose	More steady-state levels (smaller frequent doses → less fluctuation)
Volume per dose	Larger volume (weight-based) → single infusion	Smaller aliquots at multiple sites
Systemic reactions	Higher risk of infusion-related reactions (headache, fever, chills, myalgia, nausea; rare anaphylaxis)	Local site reactions common (redness, swelling) but systemic reactions rare
Advantages	Established; less frequent; can give higher doses	Home therapy → less hospital visits → better quality of life for child and family; fewer systemic side effects; steadier Ig levels
Paediatric preference	Often started as IVIG initially → then transition to SCIG once stable and family trained	Increasingly preferred in paediatrics for quality of life

IVIG / SCIG replacement ^[3] — both routes are used for antibody deficiencies including CVID and XLA.

Why SCIG Is Increasingly Preferred in Paediatrics

For a school-age child, monthly IVIG means a day off school every 3–4 weeks, sitting in a hospital for 3–4 hours with an IV line — not great for a child's quality of life or psychosocial wellbeing. SCIG allows the family to administer treatment at home, in the evening or at weekends, with minimal disruption. The steady-state levels also reduce the "trough effect" — some children feel unwell in the days before their next IVIG dose as IgG levels drop. SCIG smooths this out.

Parameter	Details
Standard dose	400–600 mg/kg/month (whether given as IVIG q3–4 weekly or SCIG divided weekly)
Starting dose	Typically start at 400 mg/kg/month and titrate based on clinical response and trough IgG levels
Target trough IgG	> 5 g/L at minimum; many centres now aim for > 7–8 g/L (or even higher) based on clinical response — the target is individualised
Titration	Increase dose if breakthrough infections persist despite adequate trough levels; some children with established bronchiectasis need higher targets (> 8 g/L)
First infusion precautions	Start slowly (0.5–1 mL/kg/hour for IVIG), increase rate gradually; have resuscitation equipment available; pre-medication with paracetamol ± antihistamine if history of infusion reactions

Pharmacokinetics explained from first principles:

IVIG is a pooled human IgG product from thousands of donors → provides broad-spectrum protective antibodies against common pathogens
IgG half-life is ~21 days → hence q3–4 weekly dosing
After IVIG infusion: IgG peaks immediately → distributes from intravascular to extravascular space over 3–5 days → then slow catabolism
Trough level (measured just before next dose) reflects the nadir of protection
SCIG provides the same total monthly dose but split into smaller frequent aliquots → avoids the peak-trough swings

Parameter	Frequency	Purpose
Trough IgG level	Every 3–6 months (just before next IVIG dose; or at any time on SCIG since levels are steady)	Ensure adequate replacement; titrate dose
Clinical infection diary	Ongoing (family keeps record)	Assess efficacy — are infections reducing?
Infusion diary	Each infusion	Document dose, rate, site reactions, systemic symptoms
LFT, RFT	6-monthly	IVIG can rarely cause transient hepatitis or renal impairment
CBC	6-monthly	Monitor for haemolysis (IVIG contains anti-A/anti-B isoagglutinins → can cause haemolytic anaemia in non-O blood group recipients), cytopenias

Adverse Effect	Mechanism	Management
Infusion-related reactions (headache, fever, chills, myalgia, nausea, flushing)	Complement activation, cytokine release from immune complexes	Slow infusion rate; pre-medicate with paracetamol ± antihistamine; switch to SCIG if persistent
Anaphylaxis (rare but important)	Anti-IgA antibodies in patients with complete IgA deficiency → IgA in the IVIG product triggers anaphylaxis	Use IgA-depleted IVIG preparations in patients with complete IgA deficiency and anti-IgA antibodies; OR use SCIG (lower risk)
Aseptic meningitis	Unclear; possibly immune-complex-mediated meningeal inflammation	Supportive; slow rate; consider SCIG
Haemolytic anaemia	Passive transfer of anti-A/anti-B isoagglutinins in IVIG → haemolysis in non-O blood group recipients	Monitor DAT, reticulocytes post-infusion; use products with low isoagglutinin titre
Thrombotic events (rare in children)	Increased serum viscosity; immune complex activation of coagulation	Ensure adequate hydration; slow infusion
Renal impairment (rare)	Osmotic nephropathy from sucrose-containing IVIG	Use sucrose-free preparations; ensure hydration
Local site reactions (SCIG)	Histamine release from dermal mast cells	Rotate injection sites; warm product to room temperature; topical ice/local anaesthetic cream before injection

Exam Pearl — IgA Deficiency and Anaphylaxis Risk

A child with complete IgA deficiency can develop anti-IgA IgE or IgG antibodies. If they then receive a blood product or IVIG containing IgA, they can develop anaphylaxis. This is why:

Check IgA level before starting IVIG
If IgA is undetectable and anti-IgA antibodies are present → use IgA-depleted preparations
SCIG has a lower risk of systemic anaphylaxis (subcutaneous absorption is slower)

Note: Selective IgA deficiency can coexist with or progress to CVID — so this is a real clinical consideration.

Consent and assent: Explain the lifelong nature of treatment to caregivers. For children ≥ 7 years (Gillick competence developing), engage the child in age-appropriate discussion about why they need regular treatment
SCIG training: Caregivers (and older children/adolescents) are trained by immunology nurse specialists in sterile technique, site rotation, recognising adverse reactions
Psychosocial support: Chronic illness with regular injections/infusions can be distressing — offer child psychology support, peer support groups
School liaison: Provide school with an individualised healthcare plan; educate teachers about infection risk and when to notify parents
Transition planning: Adolescents approaching 16–18 years should be gradually transitioned to adult immunology services with structured handover

Treatment: Ig replacement, prophylactic antibiotics ^[7]

Even with optimal Ig replacement, mucosal immunity remains compromised (IgA is NOT replaced by IVIG/SCIG — these products contain only IgG). Therefore, prophylactic antibiotics reduce the bacterial burden at mucosal surfaces and slow the progression of bronchiectasis.

Antibiotic	Dose (Paediatric)	Mechanism / Rationale	When to Use
Co-trimoxazole (Septrin) (trimethoprim-sulphamethoxazole)	TMP 2–4 mg/kg/day (prophylactic dose, lower than treatment dose)	Broad-spectrum coverage against common sinopulmonary pathogens (S. pneumoniae, H. influenzae, Moraxella); also provides PJP prophylaxis if any T-cell concern	First-line prophylactic antibiotic; check G6PD status before starting (sulphonamide component can cause haemolysis in G6PD deficiency — particularly relevant in Hong Kong where G6PD deficiency prevalence is ~4–5% in males)
Azithromycin	10 mg/kg once weekly or 5 mg/kg three times weekly	Macrolide — anti-bacterial + anti-inflammatory (reduces airway neutrophilic inflammation independent of antimicrobial effect; same principle as in CF bronchiectasis); covers atypical organisms (Mycoplasma)	Alternative to co-trimoxazole; preferred in established bronchiectasis (anti-inflammatory benefit); well-tolerated in children

Additional antibiotic considerations:

Prompt treatment of acute infections: Low threshold for starting empirical antibiotics at first sign of infection (fever, increased sputum, worsening cough); do NOT wait for culture results
Antibiotic choice for acute exacerbations: Amoxicillin-clavulanate (first-line for sinopulmonary), target Pseudomonas with ciprofloxacin/IV piperacillin-tazobactam if previously colonised
Antifungal prophylaxis: Not routinely needed in CVID (unlike CGD or SCID), as fungal susceptibility is not a major feature of isolated antibody deficiency

Why Not Just Use Higher Dose IVIG Instead of Antibiotics?

Even with IgG levels maintained > 8 g/L, IVIG does not restore mucosal IgA. IgA is the dominant immunoglobulin at mucosal surfaces (respiratory, GI), and its deficiency in CVID leaves these surfaces vulnerable regardless of serum IgG level. Prophylactic antibiotics bridge this gap by directly reducing bacterial colonisation at mucosal sites.

5. Pillar 3 — Management of Specific Complications

Autoimmune phenomena such as idiopathic thrombocytopenic purpura and autoimmune haemolytic anaemia in up to 25% ^[1]

Treatment	Mechanism	Paediatric Dosing / Notes
Corticosteroids (first-line)	Suppress autoantibody production + reduce RES-mediated destruction	Prednisolone 1–2 mg/kg/day (max 60 mg) → taper over weeks; in paediatrics, minimise steroid duration due to growth suppression, adrenal suppression, metabolic effects
IVIG (high-dose)	Saturates Fc receptors on splenic macrophages → reduces clearance of antibody-coated platelets/RBCs; also modulates B-cell function	1–2 g/kg as a single dose or split over 2 days; rapid but temporary effect (~2–4 weeks)
Rituximab (anti-CD20)	Depletes CD20+ B cells → reduces autoantibody production	375 mg/m²/dose IV × 4 weekly doses; increasingly used in steroid-refractory ITP/AIHA in CVID; risk of further hypogammaglobulinaemia (already present) → ensure Ig replacement is continued
Mycophenolate mofetil (MMF)	Inhibits inosine monophosphate dehydrogenase → blocks purine synthesis in lymphocytes → selective lymphocyte suppression	600 mg/m²/dose BD; steroid-sparing agent
Splenectomy	Removes the site of platelet/RBC destruction + removes a major source of autoantibody production	Last resort in paediatrics; increased post-splenectomy infection risk (encapsulated organisms) → must ensure: pre-splenectomy vaccinations (pneumococcal, meningococcal, Hib), lifelong penicillin prophylaxis, medical alert bracelet
TPO receptor agonists (eltrombopag, romiplostim)	Stimulate thrombopoietin receptor → increase platelet production	Used in refractory ITP; eltrombopag: oral, 25–75 mg/day in children ≥ 1 year; monitor for hepatotoxicity

Special Caution — Splenectomy in CVID

Splenectomy in CVID is a high-risk decision. These children already have antibody deficiency → adding functional asplenia dramatically increases the risk of overwhelming post-splenectomy infection (OPSI) from encapsulated bacteria. If splenectomy is unavoidable:

Vaccinate ≥ 2 weeks before surgery (PCV13/PPSV23, MenACWY, MenB, Hib) — though vaccine responses may be poor in CVID
Lifelong penicillin V prophylaxis (phenoxymethylpenicillin 125–250 mg BD depending on age)
Ensure continued IVIG/SCIG replacement
Educate family about fever as an emergency

Granulomatous disease in 8–22% ^[1]

Treatment	Mechanism	Notes
Corticosteroids	Suppress granulomatous inflammation	Often the initial treatment; may achieve radiological improvement; taper to lowest effective dose
Rituximab + azathioprine	Rituximab depletes B cells involved in lymphocytic infiltration; azathioprine (a purine antimetabolite) provides maintenance immunosuppression	Combination therapy increasingly used as first-line for GLILD (based on evidence from UK PID consortium); azathioprine dose: 1–3 mg/kg/day; check TPMT activity before starting (risk of severe myelosuppression if TPMT-deficient)
Mycophenolate mofetil (MMF)	Alternative to azathioprine for maintenance	Used if azathioprine not tolerated
Abatacept	CTLA-4-Ig fusion protein → restores immune checkpoint	Specifically effective if underlying monogenic cause is CTLA-4 haploinsufficiency or LRBA deficiency (abatacept replaces the missing CTLA-4 function)
Sirolimus (rapamycin)	mTOR inhibitor → suppresses lymphoproliferation	Used in refractory lymphoproliferation; also effective in some APDS cases

Intermittent or chronic diarrhoea ^[1]

Cause	Treatment
Giardia lamblia	Metronidazole 7.5 mg/kg TDS × 5–7 days (paediatric dose); may need prolonged or repeated courses in CVID due to impaired mucosal clearance
Nodular lymphoid hyperplasia	Usually no specific treatment needed unless causing obstruction; optimise Ig replacement
IBD-like colitis	Treat as per IBD protocols (5-ASA, corticosteroids, immunomodulators); may be steroid-dependent
Malabsorption / villous atrophy	Nutritional support: dietitian involvement, supplementation of fat-soluble vitamins (A, D, E, K), iron, zinc, folate; consider elemental or semi-elemental formula in severe cases

Recurrent respiratory tract infections with the development of bronchiectasis ^[1]

Intervention	Rationale
Airway clearance techniques	Physiotherapy, positive expiratory pressure (PEP) devices, oscillatory devices (Flutter, Acapella) → mobilise and clear secretions from permanently dilated airways
Prompt antibiotic treatment of exacerbations	Culture sputum; treat common pathogens (S. pneumoniae, H. influenzae, Pseudomonas); typical course 10–14 days
Prophylactic azithromycin	Anti-inflammatory + antimicrobial → reduces exacerbation frequency (evidence extrapolated from CF and non-CF bronchiectasis trials)
Annual influenza vaccination	Inactivated influenza vaccine is safe; may not mount full antibody response but provides partial protection; given alongside Ig replacement
Inhaled hypertonic saline (7%)	Osmotic agent → draws water into airways → improves mucociliary clearance; well-established in CF, increasingly used in non-CF bronchiectasis

Increased risk of gastrointestinal and lymphoid malignancies ^[1]

Lymphoma: Any new or progressive lymphadenopathy must be biopsied to distinguish reactive lymphoproliferation from lymphoma; standard chemotherapy protocols if confirmed
Gastric cancer: Consider periodic upper GI endoscopy in patients with chronic atrophic gastritis; H. pylori eradication if positive
General cancer surveillance: No universally agreed screening protocol, but heightened clinical vigilance and low threshold for biopsy

6. Pillar 4 — Vaccination, Surveillance, and Long-Term Monitoring

Vaccine Type	Safety	Efficacy	Recommendation
Inactivated / killed vaccines (influenza, hepatitis B, pneumococcal conjugate, meningococcal, etc.)	Safe	Likely poor response (the underlying defect is inability to mount antibody responses) — but may provide partial benefit, especially cellular immunity for some vaccines	Give routinely — even if response is suboptimal, there is no harm and potential partial benefit; annual inactivated influenza vaccine recommended
Live vaccines (MMR, varicella, rotavirus, BCG, live influenza)	Potentially dangerous if significant T-cell defect → live organisms may cause disseminated infection	Poor response	Individualise: If CVID is purely antibody-mediated with proven normal T-cell function → live vaccines may be given cautiously (expert immunology opinion required). If any T-cell abnormality → avoid all live vaccines. Household contacts should receive inactivated alternatives where possible.

High Yield — Live Vaccines in Immunodeficiency

The general rule: live vaccines are contraindicated in significant T-cell immunodeficiency (SCID, CID, DiGeorge). For CVID, the decision is nuanced because most CVID patients have intact T-cell function — but since ~50% have some T-cell abnormality, the default in many centres is to avoid live vaccines unless T-cell function has been formally confirmed as normal. Always discuss with the immunology team.

Frequency	Assessment
Every 3–6 months	Trough IgG level; CBC (cytopenias screen); infection diary review; growth parameters (weight, height, BMI centile)
Every 6–12 months	LFT, RFT; clinical review by paediatric immunologist; developmental assessment in younger children
Annually	Pulmonary function tests (spirometry ± DLCO in children > 6 years); HRCT thorax (baseline then as clinically indicated — not necessarily annually unless GLILD present); abdominal ultrasound (splenomegaly monitoring)
As indicated	DAT + haemolysis screen if new anaemia; endoscopy if new/worsening GI symptoms; lymph node biopsy if progressive lymphadenopathy; bone density scan if malabsorption/steroid use

Begin structured transition planning from age 12–14 years
Dual clinic attendance (paediatric + adult immunology) from age ~16
Complete handover by 18 years
Ensure the adolescent understands: their diagnosis, why Ig replacement is lifelong, how to self-administer SCIG, when to seek urgent medical attention, reproductive implications (genetic counselling)

7. Definitive / Curative Therapy — HSCT and Gene Therapy

Aspect	Details
Role in CVID	NOT standard treatment for typical CVID — reserved for severe cases with life-threatening complications (refractory cytopenias, severe GLILD, recurrent life-threatening infections despite maximal Ig replacement) or when a monogenic cause amenable to HSCT is identified (e.g., LRBA deficiency, APDS, CTLA-4 haploinsufficiency with severe disease)
Rationale	Replace the defective haematopoietic system (including B-cell lineage) with a functional donor system → restores immunoglobulin production
Considerations	High morbidity and mortality from HSCT (graft-vs-host disease, graft failure, transplant-related infections); therefore risk-benefit must be carefully assessed; HLA-matched sibling donor is ideal but not always available

HSCT ^[3] is listed as a treatment for several primary immunodeficiencies (SCID, CGD, WAS, IL-10R deficiency, severe CVID).

Monogenic Diagnosis	Targeted Therapy	Mechanism
CTLA-4 haploinsufficiency	Abatacept (CTLA-4-Ig)	Replaces the missing immune checkpoint protein → restores T-cell regulation
LRBA deficiency	Abatacept	LRBA traffics CTLA-4 to the cell surface → LRBA deficiency = functional CTLA-4 deficiency → abatacept bypasses this
APDS (PIK3CD GOF)	Leniolisib (PI3Kδ inhibitor, FDA-approved 2023 for APDS in patients ≥ 12 years)	Directly inhibits the overactive PI3Kδ enzyme → restores normal signalling
APDS	Sirolimus (mTOR inhibitor)	PI3K → AKT → mTOR pathway is hyperactivated in APDS → sirolimus blocks downstream

Precision Medicine in CVID — The Genetic Revolution

This is why genetic testing matters so much. A child labelled "CVID" who is found to have CTLA-4 haploinsufficiency can receive abatacept — a targeted therapy that addresses the root cause. Similarly, APDS patients can receive leniolisib. Without genetic testing, these patients receive only supportive care (Ig replacement + steroids). With genetic testing, they get disease-modifying therapy. Always pursue genetic workup.

Complication	First-Line Treatment	Second-Line	Key Paediatric Consideration
Recurrent infections	Ig replacement (IVIG or SCIG) + prophylactic antibiotics ^[7]	Higher Ig dose; antibiotic rotation	Ensure age-appropriate dosing; SCIG for quality of life
ITP	Corticosteroids; high-dose IVIG	Rituximab; TPO agonists; splenectomy (last resort)	Monitor growth on steroids; pre-splenectomy vaccines + lifelong penicillin
AIHA	Corticosteroids	Rituximab; MMF; splenectomy	DAT monitoring; folate supplementation
GLILD	Corticosteroids; rituximab + azathioprine	MMF; abatacept (if CTLA-4/LRBA); sirolimus	Check TPMT before azathioprine
Bronchiectasis	Chest physiotherapy; prophylactic azithromycin; prompt Abx for exacerbations	Inhaled hypertonic saline; HRCT monitoring	Age-appropriate airway clearance devices; PFT monitoring
Chronic diarrhoea	Treat Giardia (metronidazole); nutritional support	Endoscopy + biopsy; IBD-specific treatment if indicated	Fat-soluble vitamin supplementation; dietitian
Lymphoproliferation	Biopsy (exclude lymphoma); immunosuppression	Rituximab; sirolimus; HSCT if monogenic	Low threshold for biopsy in progressive lymphadenopathy
Malignancy	Standard oncology protocols	—	Cancer surveillance; gastric cancer screening in chronic atrophic gastritis

Intervention	Contraindication / Caution
IVIG	Severe IgA deficiency with anti-IgA antibodies → anaphylaxis risk; use IgA-depleted product or switch to SCIG
Co-trimoxazole	G6PD deficiency (sulphonamide component → haemolysis); allergy to sulphonamides
Azathioprine	TPMT deficiency → severe myelosuppression; always check TPMT activity before starting
Rituximab	Hepatitis B reactivation risk → check HBsAg/anti-HBc before use; may worsen hypogammaglobulinaemia
Live vaccines	Avoid if T-cell function uncertain or impaired
Splenectomy	Increased OPSI risk; must ensure pre-splenectomy vaccines + lifelong penicillin prophylaxis + medical alert
Corticosteroids (prolonged)	Growth suppression in children; adrenal suppression; metabolic syndrome; osteoporosis; cataracts

High Yield Summary — Management of CVID

Four pillars:

Immunoglobulin replacement (IVIG q3–4 weeks or SCIG weekly/biweekly; target trough IgG > 5–8 g/L; titrate to clinical response)
Prophylactic antibiotics (co-trimoxazole or azithromycin; check G6PD before co-trimoxazole)
Treat complications (autoimmune cytopenias: steroids → rituximab → splenectomy; GLILD: steroids + rituximab/azathioprine; chronic diarrhoea: treat Giardia + nutritional support; bronchiectasis: physiotherapy + prompt antibiotics)
Surveillance (6–12 monthly bloods, annual PFTs/imaging, growth/development monitoring, cancer vigilance)

Precision medicine: Genetic testing may reveal monogenic causes (CTLA-4 → abatacept; APDS → leniolisib/sirolimus; LRBA → abatacept). HSCT reserved for severe refractory cases or identified monogenic disease.

Paediatric priorities: Age-appropriate dosing, SCIG for quality of life, growth monitoring on steroids, developmental assessment, family education, school liaison, transition planning to adult services, live vaccine caution.

Active Recall - Management of CVID

References

^[1] Lecture slides: Investigations of Imm Disorders 2025.pdf (p15 — CVID section) ^[3] Senior notes: Jerry's immunodeficiencies.pdf (antibody deficiencies treatment, HSCT indications) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p410 — Primary Immunodeficiency, CVID features) ^[6] Lecture slides: Investigations of Imm Disorders 2025.pdf (p14 — CVID case lab results, reluctant to receive IVIG) ^[7] GC Lecture slides: GC 096. Why do I always get sick.pdf (p23 — Antibody immunodeficiencies treatment)

Complications of CVID in Paediatrics

The complications of CVID are, in many ways, the disease itself. CVID is not simply "recurrent infections" — it is a systemic disorder of immune dysregulation that damages multiple organ systems over time. Understanding complications from first principles means recognising that they stem from two core failures: failure of humoral immunity (→ infections → structural damage) and failure of immune regulation (→ autoimmunity, lymphoproliferation, granulomatous disease, malignancy).

The clinical phenotype of complications determines prognosis far more than the Ig levels alone. Children with the infection-only phenotype have the best outcomes; those with autoimmunity, lymphoproliferation, or granulomatous disease have significantly higher morbidity and mortality.

Category	Mechanism (First Principles)	Examples
Infectious	Defective Ig production ^[4] → loss of opsonisation and mucosal defence → recurrent infections → progressive structural damage	Bronchiectasis, chronic sinusitis, otitis media, chronic diarrhoea
Autoimmune	Loss of peripheral tolerance (defective Tregs, impaired B-cell selection) → self-reactive lymphocytes escape deletion → autoantibody production	ITP, AIHA ^[1], Evans syndrome, autoimmune thyroiditis, pernicious anaemia
Lymphoproliferative	Chronic antigenic stimulation + defective immune surveillance → polyclonal lymphocyte expansion	Splenomegaly, lymphadenopathy, nodular lymphoid hyperplasia of small bowel ^[1]
Granulomatous	Persistent antigen challenge + aberrant macrophage/T-cell response → granuloma formation	Granulomatous disease in 8–22% ^[1] — GLILD, granulomatous hepatitis
Malignant	Chronic immune activation + impaired tumour surveillance + EBV-driven lymphoproliferation	Increased risk of gastrointestinal and lymphoid malignancies ^[1]
Treatment-related	Consequences of lifelong immunosuppression and Ig replacement	IVIG reactions, steroid side effects, post-splenectomy infection
Growth and developmental (paediatric-specific)	Chronic illness, malabsorption, repeated hospitalisations, medication side effects	Failure to thrive, short stature, delayed puberty, psychosocial impact

2. Infectious Complications

Recurrent respiratory tract infections with the development of bronchiectasis ^[1] Recurrent sinopulmonary ("idiopathic" bronchiectasis) and gastrointestinal infections (chronic diarrhoea) ^[7]

Why does bronchiectasis develop?

The pathophysiology follows a vicious cycle (Cole's vicious circle hypothesis):

Defective Ig production ^[4] → loss of IgG opsonisation + IgA mucosal defence
→ Encapsulated bacteria (S. pneumoniae, H. influenzae ^[7]^[11]) colonise the lower airways
→ Neutrophilic inflammation → release of proteases (neutrophil elastase, MMP) and reactive oxygen species
→ Destruction of bronchial wall elastic tissue and cartilage
→ Permanent bronchial dilatation = bronchiectasis
→ Impaired mucociliary clearance in dilated, damaged airways
→ Further bacterial colonisation → more inflammation → more damage → cycle continues

Paediatric-specific considerations:

Bronchiectasis is the single most important cause of morbidity in paediatric CVID
Once established, it is irreversible — hence the urgency of early diagnosis and Ig replacement to prevent it
Diagnostic delay is the biggest risk factor — the average delay between symptom onset and CVID diagnosis is 6–8 years, during which irreparable lung damage accumulates
Switched memory B cell absent → more prone to recurrent respiratory infections and development of bronchiectasis ^[6]
Detection: HRCT thorax (signet ring sign, tram tracks, dilated airways); serial pulmonary function tests (obstructive or mixed pattern)
Pathogen shift over time: initially S. pneumoniae and H. influenzae → with progressive bronchiectasis, Pseudomonas aeruginosa colonisation occurs (worse prognosis, harder to eradicate)

Why Early Diagnosis Prevents Bronchiectasis

The entire point of early diagnosis and prompt Ig replacement is to break Cole's vicious cycle BEFORE permanent structural damage occurs. Once bronchial walls are destroyed, no amount of Ig replacement can reverse the dilatation. This is why CVID carries the motto: "diagnose early, treat early, save the lungs."

Complication	Pathophysiology	Consequence in Children
Chronic rhinosinusitis	IgA deficiency at nasal/sinus mucosa → bacterial colonisation → chronic mucosal inflammation → mucosal hypertrophy → sinus ostia obstruction → retained secretions → secondary infection cycle	Nasal obstruction, mouth breathing, hyponasal speech, poor sleep quality, headaches; may develop nasal polyps
Recurrent/chronic otitis media	IgA deficiency at Eustachian tube mucosa + middle ear → bacterial colonisation; children are anatomically predisposed (shorter, more horizontal Eustachian tube)	Conductive hearing loss → speech and language delay (critical in preschool children); tympanic membrane perforation, cholesteatoma; may require grommets (ventilation tubes)

In paediatrics, always assess hearing in any child with CVID — recurrent otitis media causes conductive hearing loss that, if undetected, impairs speech, language, and academic development. Refer for audiology assessment.

Intermittent or chronic diarrhoea ^[1]

Pathogen	Why Susceptible?	Consequence
Giardia lamblia ^[7]^[11]	IgA is the primary defence against Giardia at the intestinal mucosa; IgA deficiency → Giardia attaches to enterocytes and causes villous atrophy	Chronic watery diarrhoea, malabsorption, steatorrhoea, abdominal bloating, failure to thrive
Enteroviruses ^[7]^[11]	Antibody-mediated neutralisation is the primary defence against enteroviruses; in hypogammaglobulinaemia, enteroviruses can persist and disseminate	Chronic meningoencephalitis (rare but devastating — progressive neurological deterioration); chronic enteroviral GI infection
Norovirus, Campylobacter, Salmonella	Mucosal IgA deficiency → impaired barrier function	Chronic or recurrent gastroenteritis

Enteroviral Meningoencephalitis — A Rare But Devastating Complication

Chronic enteroviral meningoencephalitis is unique to antibody deficiency (XLA and CVID). Enteroviruses (echovirus, coxsackievirus) normally cleared by neutralising antibodies can persist in the CNS, causing a slowly progressive, ultimately fatal encephalitis. It is rare but must be considered in any child with antibody deficiency who develops neurological symptoms. High-dose IVIG (intrathecal in some cases) is the treatment.

Infection	Setting	Notes
Recurrent pneumonia	Before or despite Ig replacement	Each episode risks further bronchial damage; common pathogens: S. pneumoniae, H. influenzae, Mycoplasma
Septicaemia	Encapsulated bacteria breaching mucosal barriers	Risk reduced significantly by Ig replacement but not eliminated; risk further increased post-splenectomy
Herpes virus infections (less common than in CID)	If T-cell dysfunction coexists (~50% of CVID patients have some T-cell abnormality)	CMV, EBV reactivation; chronic or recurrent HSV/VZV

3. Autoimmune Complications

Autoimmune phenomena such as idiopathic thrombocytopenic purpura and autoimmune haemolytic anaemia in up to 25% ^[1]

Why does an immunodeficiency cause autoimmunity?

This seems paradoxical at first — the immune system is deficient, yet it attacks self. The explanation:

Defective Tregs (regulatory T cells) → failure of peripheral tolerance → self-reactive lymphocytes escape suppression
Chronic antigenic stimulation from recurrent infections → continuous immune activation → bystander activation of autoreactive clones
Defective B-cell selection → failure to delete or anergise self-reactive B cells in the germinal centre → autoantibody production
Molecular mimicry → cross-reactivity between microbial antigens and self-antigens during chronic infection

Complication	Prevalence	Mechanism	Clinical Features	Key Points
Immune thrombocytopenia (ITP) ^[1]	~10–15%	Anti-platelet antibodies (anti-GPIIb/IIIa, anti-GPIb/IX) → platelet opsonisation → destruction by splenic macrophages	Petechiae, purpura, mucosal bleeding (epistaxis, gum bleeding), menorrhagia in adolescent girls	May be the presenting feature of CVID, preceding recurrent infections by years; always check Ig levels in any child with chronic/recurrent ITP
Autoimmune haemolytic anaemia (AIHA) ^[1]	~5–10%	IgG anti-RBC antibodies (warm AIHA) → extravascular haemolysis in spleen	Pallor, fatigue, jaundice, dark urine, splenomegaly; positive DAT (IgG ± C3d)	Warm AIHA predominates in CVID
Evans syndrome	~5%	ITP + AIHA co-occurring (with or without autoimmune neutropenia)	Combined features; often chronic/relapsing	Evans syndrome in a child should ALWAYS prompt investigation for underlying immunodeficiency (CVID, ALPS)
Autoimmune neutropenia	~5–8%	Anti-neutrophil antibodies → neutrophil destruction	Recurrent bacterial infections with low ANC; may compound the existing infection susceptibility	Can worsen the infectious phenotype

High Yield — ITP as a Presenting Feature of CVID

In paediatric practice, ITP is extremely common (most common cause of thrombocytopenia in otherwise well children). Most childhood ITP is self-limiting post-viral. However, if ITP is chronic (> 12 months), recurrent, or accompanied by AIHA (Evans syndrome), always check immunoglobulin levels. Autoimmune cytopenias, interstitial lung disease, inflammatory bowel disease ^[7] are listed as features of antibody immunodeficiency alongside recurrent infections. Missing the underlying CVID diagnosis in a child "labelled" with chronic ITP delays Ig replacement and allows preventable lung damage.

Complication	Mechanism	Prevalence	Clinical Impact
Autoimmune thyroiditis (Hashimoto)	Anti-thyroid antibodies (anti-TPO, anti-thyroglobulin) → lymphocytic infiltration → thyroid destruction	~5–10%	Hypothyroidism → fatigue, weight gain, constipation, growth deceleration; monitor TSH/fT4 regularly
Pernicious anaemia	Anti-intrinsic factor or anti-parietal cell antibodies → impaired B12 absorption	~3–5%	Megaloblastic anaemia, neurological symptoms (peripheral neuropathy, subacute combined degeneration); check B12 levels
Type 1 diabetes mellitus	Anti-islet antibodies → β-cell destruction	Rare but reported	Polyuria, polydipsia, weight loss, DKA
Autoimmune hepatitis	Anti-smooth muscle or anti-LKM antibodies → hepatocyte destruction	~3%	Elevated transaminases, jaundice; must distinguish from granulomatous hepatitis (different mechanism and treatment)
Inflammatory arthritis	Immune complex deposition ± loss of tolerance to synovial antigens	~5–10%	Joint pain, swelling, morning stiffness; resembles RA
Alopecia areata / Vitiligo	Autoimmune targeting of hair follicle melanocytes (alopecia) or skin melanocytes (vitiligo)	Variable	Cosmetically distressing → significant psychosocial impact in children/adolescents

4. Lymphoproliferative Complications

Polyclonal lymphoproliferation with splenomegaly, lymphadenopathy or nodular lymphoid hyperplasia of the small bowel occurs in approximately 1/3 of patients ^[1]

Why does lymphoproliferation occur?

In CVID, the immune system is in a state of chronic, ineffective activation:

Recurrent infections → persistent antigenic stimulation → polyclonal lymphocyte expansion
Defective immune regulation (impaired Tregs, loss of checkpoints like CTLA-4) → proliferating lymphocytes are not adequately restrained
This is polyclonal (reactive), not monoclonal (malignant) — but the line between the two can be thin, and lymphoproliferative disease can progress to lymphoma

Aspect	Details
Prevalence	~25–30% of CVID patients
Mechanism	Reactive lymphoid hyperplasia of splenic white pulp + sequestration of antibody-coated blood cells (ITP, AIHA) + extramedullary haematopoiesis
Clinical significance in children	Left upper quadrant fullness/pain; hypersplenism → worsened cytopenias (pancytopenia); rupture risk with trauma (important for sports participation counselling — contact sports may need restriction in significant splenomegaly)
Monitoring	Serial abdominal ultrasound; clinical examination at each visit

Aspect	Details
Mechanism	Polyclonal lymphoid hyperplasia of lymph nodes; chronic antigenic stimulation
Key concern	Must distinguish from lymphoma — any node that is rapidly enlarging, fixed, hard, or associated with B symptoms (fever, night sweats, weight loss > 10%) requires biopsy
Approach	Low threshold for excisional lymph node biopsy in CVID patients with progressive or atypical lymphadenopathy

Aspect	Details
Prevalence	Part of the ~1/3 with lymphoproliferation
Mechanism	Polyclonal lymphoid follicle expansion in intestinal submucosa → visible as multiple nodules on endoscopy
Consequences	Abdominal pain, diarrhoea, malabsorption; can mimic IBD; very rarely undergoes malignant transformation
Detection	Endoscopy + biopsy; CT/MR enterography

5. Granulomatous Complications

Granulomatous disease in 8–22% ^[1]

Why non-caseating granulomas?

The exact mechanism is not fully understood, but the leading hypothesis is:

Persistent antigen exposure (from chronic infections that cannot be adequately cleared) →
Macrophage activation → failure to resolve the inflammatory response (possibly due to impaired T-cell regulation) →
Macrophage fusion into epithelioid and giant cells → granuloma formation
Histologically identical to sarcoidosis (non-caseating granulomas) — indeed, some patients initially diagnosed with sarcoidosis are later found to have CVID

Aspect	Details
Prevalence	~8–22%
Pathology	Combination of non-caseating granulomas + lymphocytic interstitial pneumonitis (LIP) + follicular bronchiolitis
Clinical features	Progressive dyspnoea, non-productive cough (insidious onset); may be asymptomatic on HRCT
Radiology	HRCT: ground-glass opacities, nodules (may coalesce), lower lobe predominance; can mimic sarcoidosis or lymphoma
PFTs	Restrictive pattern (reduced FVC, reduced TLC); reduced DLCO
Prognosis	Progressive if untreated → respiratory failure; major contributor to mortality; can improve with treatment (rituximab + azathioprine)

Aspect	Details
Pathology	Non-caseating granulomas in hepatic parenchyma
Clinical features	Hepatomegaly, elevated ALP/GGT, may progress to nodular regenerative hyperplasia (NRH) → portal hypertension
Distinction from autoimmune hepatitis	Granulomatous hepatitis: cholestatic LFT pattern (ALP/GGT ↑); autoimmune hepatitis: hepatitic pattern (ALT/AST ↑)

Spleen → granulomatous splenitis → worsened splenomegaly
Lymph nodes → granulomatous lymphadenitis (must distinguish from TB, sarcoidosis, lymphoma)
Skin → cutaneous granulomas (papules, nodules)
Brain (rare) → granulomatous CNS disease → seizures, neurological deficits

Increased risk of gastrointestinal and lymphoid malignancies ^[1]

Malignancy	Relative Risk	Mechanism	Key Points
Non-Hodgkin lymphoma (NHL)	5–12× general population	Chronic immune activation → polyclonal lymphoproliferation → accumulation of genetic mutations → monoclonal transformation; impaired tumour immunosurveillance; EBV-driven lymphoproliferation in some cases	Most common CVID-associated malignancy; B-cell NHL predominates (DLBCL, MALT lymphoma); any progressive lymphadenopathy must be biopsied
Gastric adenocarcinoma	10–47× general population	Chronic atrophic gastritis (autoimmune) → intestinal metaplasia → dysplasia → adenocarcinoma (identical to the H. pylori → gastric cancer pathway, but here driven by autoimmune gastritis and possibly impaired mucosal immunity allowing H. pylori persistence)	Justify periodic upper GI endoscopy screening; eradicate H. pylori if positive
Hodgkin lymphoma	Increased	Similar to NHL mechanism	Less common than NHL in CVID
Other solid organ tumours	Variably increased	Impaired immune surveillance	Thymic tumours, skin cancers (especially if immunosuppressed)

Cancer in B-cell vs T-cell deficiency — comparison (from GC lecture):

B cells — antibody: Cancer outcome = Rare ^[11] T cells — cellular immunity: Increased risk of lymphoma, leukaemia, cancer ^[11]

This is important context: in pure antibody deficiency, malignancy risk is lower than in T-cell/combined defects. However, CVID is not purely antibody-mediated — many patients have T-cell abnormalities too, which explains why CVID has a higher lymphoma risk than, say, selective IgA deficiency.

Why Gastric Cancer Risk Is So High in CVID

The stomach relies on IgA for mucosal defence. In CVID, IgA deficiency → H. pylori can persist → chronic active gastritis. Additionally, autoimmune anti-parietal cell antibodies cause chronic atrophic gastritis → achlorhydria → intestinal metaplasia → dysplasia → adenocarcinoma. This pathway is identical to the well-known H. pylori → gastric cancer sequence but is accelerated in CVID by the dual insult of infection susceptibility AND autoimmune gastric destruction.

These are critically important in paediatrics and often overlooked in adult-focused teaching:

Complication	Mechanism	Assessment and Management
Failure to thrive / Growth faltering	Chronic infection → increased metabolic demands; chronic diarrhoea → malabsorption of calories and nutrients; chronic inflammation → growth suppression (IL-6, TNF → suppress growth plate); corticosteroid use → growth suppression	Serial plotting on growth charts (weight, height, head circumference); referral to paediatric endocrinology if crossing centiles; nutritional supplementation; minimise steroid exposure
Short stature	As above + potential delayed puberty from chronic illness	Growth velocity monitoring; bone age assessment if indicated; consider growth hormone if growth failure persists despite optimised treatment
Delayed puberty	Chronic illness → hypothalamic-pituitary-gonadal axis suppression; nutritional deficiency → delayed menarche/pubertal development	Tanner staging at each visit from age 8–9 (girls) or 9–10 (boys); endocrine referral if delayed
Nutritional deficiencies	Malabsorption (villous atrophy, Giardia, NLH) → deficiency of fat-soluble vitamins (A, D, E, K), iron, zinc, folate, B12	Regular monitoring of micronutrient levels; dietitian involvement; supplementation as needed
Osteoporosis / Low bone density	Vitamin D malabsorption + corticosteroid use + chronic inflammation → reduced bone mineralisation	DEXA scan if risk factors present; calcium + vitamin D supplementation; weight-bearing exercise
Hearing loss	Recurrent/chronic otitis media → conductive hearing loss; rarely sensorineural from enteroviral CNS disease	Audiology assessment; speech and language therapy referral if impaired
Developmental delay	Chronic illness → missed schooling → academic delay; hearing loss → speech/language delay; chronic enteroviral meningoencephalitis → neurodevelopmental regression	Serial developmental assessments; educational support; school liaison
Psychosocial impact	Chronic illness requiring regular infusions/injections; restriction from normal activities (sports in splenomegaly); body image concerns (steroid side effects, short stature); anxiety about health; social isolation from repeated hospitalisations	Psychology/counselling referral; peer support groups; age-appropriate disease education; support for caregivers; address school reintegration
Transition anxiety	Moving from familiar paediatric team to adult services at age 16–18	Structured transition programme; dual attendance at paediatric + adult clinics; written transition plan

Complication	Cause	Details
IVIG infusion reactions	Complement activation, cytokine release	Headache, fever, chills, myalgia, nausea; rarely anaphylaxis (especially with IgA deficiency + anti-IgA antibodies); aseptic meningitis
IVIG-induced haemolysis	Passive transfer of anti-A/anti-B isoagglutinins	Non-O blood group recipients at risk; monitor DAT and haemoglobin post-infusion
Steroid side effects (prolonged use for autoimmune complications or GLILD)	Glucocorticoid excess	Growth suppression (most critical in children — crosses the growth plate and inhibits chondrocyte proliferation), weight gain/Cushingoid features, hyperglycaemia, hypertension, osteoporosis, cataracts, adrenal suppression, mood changes, immunosuppression compounding existing immunodeficiency
Overwhelming post-splenectomy infection (OPSI)	Loss of splenic filtration function after splenectomy (performed for refractory ITP/AIHA)	Rare but life-threatening; > 50% caused by S. pneumoniae ^[12]; lifetime risk ~5%, most within first 2 years ^[12]; requires pre-splenectomy vaccination (pneumococcal, meningococcal, Hib, influenza) + lifelong penicillin prophylaxis ^[12]
Rituximab-related hypogammaglobulinaemia	CD20+ B-cell depletion → further reduces already impaired Ig production	May worsen humoral deficiency; must continue Ig replacement; monitor B-cell recovery
Azathioprine myelosuppression	TPMT deficiency → toxic accumulation of thioguanine nucleotides → bone marrow suppression	Check TPMT activity before starting; regular FBC monitoring

Splenectomy in CVID — A Perfect Storm for OPSI

The combination of antibody deficiency (CVID) + functional asplenia (post-splenectomy) creates a particularly dangerous situation. The spleen filters encapsulated bacteria opsonised by antibodies — but in CVID, the antibodies are already deficient. Removing the spleen takes away the last major clearance mechanism for these organisms. This is why splenectomy in CVID carries an even higher OPSI risk than splenectomy in immunocompetent patients. Vaccination responses pre-splenectomy will also be poor (because the underlying antibody defect prevents effective vaccine responses) — so Ig replacement essentially serves as the "substitute" for both the missing antibodies AND the missing spleen.

Organ System	Complications	Prevalence	Monitoring
Respiratory	Bronchiectasis, chronic sinusitis, GLILD, recurrent pneumonia	Bronchiectasis ~50–70% by adulthood; GLILD 8–22%	HRCT, PFTs, sputum culture
Haematological	ITP, AIHA, Evans syndrome, autoimmune neutropenia	Up to 25% ^[1]	CBC q3–6 months; DAT if new anaemia
Gastrointestinal	Chronic diarrhoea (Giardia), NLH, IBD-like colitis, malabsorption, gastric cancer	Diarrhoea ~20–30%; NLH ~1/3 with lymphoproliferation	Stool studies, endoscopy, nutritional bloods
Hepatic	Granulomatous hepatitis, NRH, autoimmune hepatitis	~5–10%	LFT q6–12 months; liver USS/biopsy if abnormal
Splenic	Splenomegaly	~25–30%	Abdominal USS annually
Lymphatic	Generalised lymphadenopathy	~1/3	Clinical exam; biopsy if progressive/atypical
Malignant	NHL, gastric adenocarcinoma, Hodgkin lymphoma	NHL 5–12× risk	Clinical vigilance; biopsy threshold low
Endocrine	Autoimmune thyroiditis, T1DM, pernicious anaemia	Variable (~5–10% combined)	TSH, B12, glucose monitoring
Musculoskeletal	Inflammatory arthritis, osteoporosis	Arthritis ~5–10%	Clinical assessment; DEXA if at risk
Neurological	Chronic enteroviral meningoencephalitis (rare)	Rare	Neuro exam; CSF if symptoms
Growth/development (paediatric)	FTT, short stature, delayed puberty, hearing loss, developmental delay	Variable	Growth charts, audiology, developmental assessment
Psychosocial (paediatric)	Anxiety, depression, school absenteeism, social isolation	Common	Psychology referral; family support

Factor	Impact on Prognosis
Infection-only phenotype	Best prognosis; 20-year survival ~90% with adequate Ig replacement
Autoimmune complications	Reduced survival; Evans syndrome carries worse prognosis
Lymphoproliferative/granulomatous phenotype	Significantly reduced survival; GLILD is a major cause of death
Malignancy	Major cause of mortality; lymphoma and gastric cancer
Diagnostic delay	Longer delay → more established bronchiectasis → worse respiratory outcomes
Absent switched memory B cells	More prone to recurrent respiratory infections and development of bronchiectasis ^[6] — worse prognosis
Early Ig replacement	Protective — reduces infection frequency, slows bronchiectasis progression, improves survival

Overall mortality: CVID patients have a 2–5× higher mortality than the general population. The main causes of death are:

Respiratory failure (end-stage bronchiectasis or GLILD)
Lymphoma
Hepatic disease (NRH → portal hypertension)
Severe infection/sepsis

High Yield Summary — Complications of CVID

Infectious (most common):

Bronchiectasis (vicious cycle: infections → airway destruction → impaired clearance → more infections); single biggest cause of morbidity
Chronic sinusitis, otitis media (→ hearing loss in children)
Chronic diarrhoea (Giardia, enteroviruses)
Rare: chronic enteroviral meningoencephalitis (devastating, unique to antibody deficiency)

Autoimmune (~25%):

ITP, AIHA, Evans syndrome — may be the presenting feature before infections are recognised
Organ-specific: thyroiditis, pernicious anaemia, autoimmune hepatitis, inflammatory arthritis
Always check Ig levels in children with chronic/refractory ITP or Evans syndrome

Lymphoproliferative (~1/3):

Splenomegaly, generalised lymphadenopathy, nodular lymphoid hyperplasia of small bowel
Must always exclude lymphoma (biopsy progressive/atypical nodes)

Granulomatous (8–22%):

GLILD (non-caseating lung granulomas + lymphocytic interstitial pneumonitis) — major cause of mortality
Granulomatous hepatitis → NRH → portal hypertension

Malignancy (increased risk):

NHL (5–12× risk), gastric adenocarcinoma (10–47× risk)
Chronic immune activation + impaired tumour surveillance + EBV in some cases

Paediatric-specific:

Growth faltering, short stature, delayed puberty (chronic illness + malabsorption + steroids)
Hearing loss from recurrent otitis media → speech/language delay
Psychosocial: school absence, anxiety, social isolation; needs psychology support + school liaison

Prognostic factors:

Infection-only phenotype = best prognosis
Absent switched memory B cells, autoimmunity, lymphoproliferation, granulomas = worse prognosis
Early diagnosis + prompt Ig replacement = key to preventing irreversible lung damage

Active Recall - Complications of CVID

References

^[1] Lecture slides: Investigations of Imm Disorders 2025.pdf (p15 — CVID section) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p410 — Primary Immunodeficiency, CVID) ^[6] Lecture slides: Investigations of Imm Disorders 2025.pdf (p14 — CVID case, switched memory B cells) ^[7] GC Lecture slides: GC 096. Why do I always get sick.pdf (p23 — Antibody immunodeficiencies) ^[11] GC Lecture slides: GC 144. A child with recurrent infections Primary immunodeficiencies.pdf (p9 — B-cell vs T-cell complications, cancer risk; p10 — antibody deficiencies classification) ^[12] Senior notes: Block A - Splenomegaly_ common causes of splenomegaly; myeloproliferative diseases.pdf (p19–20 — Splenectomy complications, OPSI, vaccination)

High Yield Summary

Most common clinically significant PID (selective IgA deficiency is the most common PID overall, but CVID is the most common severe antibody deficiency).

Pathophysiology: Impaired B-cell differentiation → defective immunoglobulin production. B cells are PRESENT (unlike XLA). Switched memory B cells are characteristically absent.

Genetics: TACI (TNFRSF13B) is the most commonly implicated gene (~10–15%), along with ICOS, CD19, BAFF-R. ~85–90% have no identified monogenic cause.

Clinical features — 5 phenotypes:

Infections (~90%): sinopulmonary (sinusitis, pneumonia → bronchiectasis), GI (diarrhoea, Giardia), otitis media
Autoimmunity (~25%): ITP, AIHA, Evans syndrome, inflammatory arthritis
Lymphoproliferation (~33%): splenomegaly, lymphadenopathy, nodular lymphoid hyperplasia of small bowel
Granulomatous disease (8–22%): GLILD, granulomatous hepatitis
Malignancy: non-Hodgkin lymphoma, gastric cancer

Key pathogens: Encapsulated bacteria (S. pneumoniae, H. influenzae), Giardia, Enterovirus, Mycoplasma.

First-line Ix: CBC + diff, absolute lymphocyte count, protein/globulin, Ig profile (IgG/A/M/E), vaccine responses, HIV test, CXR. B-cell subsets (switched memory B cells).

XLA vs CVID: XLA = absent B cells, absent tonsils, males only, BTK mutation. CVID = B cells present, tonsils present, M=F, heterogeneous genetics.

Paediatric priorities: Growth assessment, developmental monitoring, age-appropriate communication, family-centred care, age-specific normal values for immunoglobulins.

High Yield Summary — Differential Diagnosis of CVID

Always exclude secondary causes first: HIV, drugs (rituximab, anti-epileptics), protein-losing states (nephrotic syndrome, PLE), malignancy, CKD.
Key primary immunodeficiency differentials:
- XLA: No B cells, no tonsils, males only, BTK mutation, presents at 4–6 months
- HIGM: ↑IgM, ↓IgG/A/E, CD40L deficiency (Type 1), PJP + Cryptosporidium susceptibility
- SCID: Very low ALC, absent thymus, presents in first months of life, fatal without HSCT
- APDS: CVID-like but with more severe lymphoproliferation, herpesvirus susceptibility, PIK3CD GOF
- CTLA-4 / LRBA deficiency: CVID with prominent autoimmunity and organ infiltration
Non-immunological mimics: CF (sweat test), PCD (nasal NO, ciliary biopsy), anatomical defects, GOR/aspiration, allergic disease.
Age is your friend: SCID → 0–3 months; XLA/HIGM → 4–6 months; CVID → ≥ 4 years.
Confirm CVID with: low IgG (+ low IgA ± low IgM), impaired vaccine responses, age ≥ 4, B cells present, exclude all above.

High Yield Summary — Diagnosis of CVID

ESID 2019 Criteria (all required):

IgG low (≥ 2 SD below age-matched mean, confirmed on 2 occasions ≥ 3 weeks apart)
Low IgA and/or IgM
Impaired vaccine responses (protein ± polysaccharide antigens)
Age ≥ 4 years
Exclusion of all other causes

Key investigations in order:

Tier 1: CBC, ALC, protein/globulin, ESR/CRP, Ig profile, SPEP, C3/C4, ANA, HIV, CXR
Tier 2: B-cell count (CD19+), B-cell subsets (switched memory B cells), vaccine responses, CD40L expression, lymphocyte proliferation, DHR
Tier 3: Genetic testing (TACI, ICOS, CD19, BAFF-R; NGS panel for expanding genes)
Tier 4: Baseline organ assessment (HRCT, PFTs, abdo USS, haemolysis screen, growth/nutrition)

Critical differentiating tests:

B cells absent → XLA, not CVID
CD40L absent → HIGM Type 1, not CVID
ALC very low / absent thymus → SCID, not CVID
DHR absent → CGD, not CVID

Paediatric pearls:

Always use age-matched Ig reference ranges
Cannot diagnose CVID before age 4 (exclude THI)
Polysaccharide vaccine responses unreliable before age 2 → use conjugate vaccine responses
ESR may be paradoxically low due to hypogammaglobulinaemia (↓rouleaux formation)

High Yield Summary — Management of CVID

Four pillars:

Immunoglobulin replacement (IVIG q3–4 weeks or SCIG weekly/biweekly; target trough IgG > 5–8 g/L; titrate to clinical response)
Prophylactic antibiotics (co-trimoxazole or azithromycin; check G6PD before co-trimoxazole)
Treat complications (autoimmune cytopenias: steroids → rituximab → splenectomy; GLILD: steroids + rituximab/azathioprine; chronic diarrhoea: treat Giardia + nutritional support; bronchiectasis: physiotherapy + prompt antibiotics)
Surveillance (6–12 monthly bloods, annual PFTs/imaging, growth/development monitoring, cancer vigilance)

High Yield Summary — Complications of CVID

Infectious (most common):

Bronchiectasis (vicious cycle: infections → airway destruction → impaired clearance → more infections); single biggest cause of morbidity
Chronic sinusitis, otitis media (→ hearing loss in children)
Chronic diarrhoea (Giardia, enteroviruses)
Rare: chronic enteroviral meningoencephalitis (devastating, unique to antibody deficiency)

Autoimmune (~25%):

ITP, AIHA, Evans syndrome — may be the presenting feature before infections are recognised
Organ-specific: thyroiditis, pernicious anaemia, autoimmune hepatitis, inflammatory arthritis
Always check Ig levels in children with chronic/refractory ITP or Evans syndrome

Lymphoproliferative (~1/3):

Splenomegaly, generalised lymphadenopathy, nodular lymphoid hyperplasia of small bowel
Must always exclude lymphoma (biopsy progressive/atypical nodes)

Granulomatous (8–22%):

GLILD (non-caseating lung granulomas + lymphocytic interstitial pneumonitis) — major cause of mortality
Granulomatous hepatitis → NRH → portal hypertension

Malignancy (increased risk):

NHL (5–12× risk), gastric adenocarcinoma (10–47× risk)
Chronic immune activation + impaired tumour surveillance + EBV in some cases

Paediatric-specific:

Growth faltering, short stature, delayed puberty (chronic illness + malabsorption + steroids)
Hearing loss from recurrent otitis media → speech/language delay
Psychosocial: school absence, anxiety, social isolation; needs psychology support + school liaison

Prognostic factors:

Infection-only phenotype = best prognosis
Absent switched memory B cells, autoimmunity, lymphoproliferation, granulomas = worse prognosis
Early diagnosis + prompt Ig replacement = key to preventing irreversible lung damage

Common Variable Immunodeficiency

1. Definition

2. Epidemiology

Incidence and Prevalence

Age of Onset

Sex Distribution

Paediatric-Specific Points

3. Risk Factors

4. Anatomy and Immunology Review — Why CVID Matters

Normal B-Cell Development and Immunoglobulin Production

The Role of T-Cell Help

Why Sinopulmonary and GI Infections?

5. Aetiology and Pathophysiology

5.1 Genetic Basis

5.2 Pathophysiology — Step by Step

5.3 Why is CVID Different from XLA (X-linked Agammaglobulinaemia)?

6. Classification

6.1 ESID/PAGID Classification of PIDs — Where CVID Sits

6.2 Freiburg Classification (Based on B-cell Phenotyping)

6.3 EUROclass Classification

6.4 Clinical Phenotype Classification

7. Clinical Features

7.1 General Approach — The "SPUR" Framework

7.2 Symptoms (with Pathophysiological Basis)

A. Recurrent Infections (~90% of patients)

B. Autoimmune Manifestations (~25% of patients)

C. Lymphoproliferation (~30% of patients)

D. Granulomatous Disease (8–22%)

E. Gastrointestinal Manifestations

F. Malignancy Risk

7.3 Signs (with Pathophysiological Basis)

7.4 Timing of Presentation (Paediatric Context)

8. Initial Evaluation Framework

First-Line Investigations (from GC 096 lecture slide — high yield)

CVID-Specific Laboratory Findings (from lecture case)

B-Cell Subset Analysis (Advanced but High Yield)

9. Salient History in Paediatric CVID

10. Comparison Table — Key Antibody Deficiencies in Paediatrics

Active Recall - CVID Overview, Epidemiology, Pathophysiology, and Clinical Features

References

1. Framework for the Differential Diagnosis

2. Differential Diagnosis Mermaid Diagram

3. Secondary Causes of Hypogammaglobulinaemia (Must Exclude First)

4. Other Primary Immunodeficiencies That Mimic CVID

A. Predominantly Antibody Deficiencies

B. Combined Immunodeficiencies (CID) — More Severe Than CVID

C. Phagocyte and Innate Immunity Defects

D. Syndromic / Combined Immunodeficiencies with Distinct Clinical Clues

5. Non-Immunological Mimics of Recurrent Infections

6. Age-Based Approach to the Differential

7. Approach to Differentiating CVID — Key Investigations

8. Summary Table — CVID vs. Its Key Differentials

Active Recall - Differential Diagnosis of CVID

1. Diagnostic Criteria

A. ESID 2019 Diagnostic Criteria for CVID

B. ICON 2016 Criteria (International Consensus)

C. Summary of Diagnostic Requirements

2. Diagnostic Algorithm

3. Investigation Modalities — Detailed Guide

Tier 1: First-Line Screening Investigations

Tier 2: Immunological Workup (Confirmatory)

Tier 3: Genetic Testing

Tier 4: Baseline Organ Assessment and Monitoring

4. Special Considerations in Paediatric Diagnosis

A. Age-Specific Immunoglobulin Interpretation

B. Vaccine Response Interpretation in Children

C. When to Refer to Paediatric Immunology

5. Putting It Together — Investigation Interpretation Flowchart

Active Recall - Diagnostic Criteria, Algorithm, and Investigations for CVID

1. Principles of Management

2. Management Algorithm

3. Pillar 1 — Immunoglobulin Replacement Therapy

A. Routes of Administration

B. Dosing (Paediatric-Specific)

C. Monitoring on Ig Replacement

D. Adverse Effects of Ig Replacement

E. Practical Considerations — Family-Centred Care

4. Pillar 2 — Prophylactic Antibiotics

5. Pillar 3 — Management of Specific Complications

A. Autoimmune Cytopenias (ITP, AIHA, Evans Syndrome)