IgA vasculitis (Henoch-Schönlein purpura) is a small-vessel vasculitis caused by IgA immune complex deposition, characterized by palpable purpura, arthralgia, abdominal pain, and glomerulonephritis, most commonly affecting children.

Exam domain	One-glance essentials
Definition / diagnosis	*IgA vasculitis = IgA1-dominant immune-complex small-vessel vasculitis* involving skin, GI tract, joints and kidneys ^[1]^[2] Renal histology is identical to IgA nephropathy; IgAV is systemic ^[2]
Epidemiology / risks	*Most common systemic vasculitis in childhood*; peak age ~6–7 years ^[1]^[2] Often follows URTI and clusters in winter/spring; adult disease has worse renal prognosis ^[2]
Core mechanism	Mucosal trigger → galactose-deficient IgA1 immune complexes → small-vessel/mesangial deposition → alternative/lectin complement activation and leukocytoclastic vasculitis ^[2] Localised complement activation explains usually normal serum C3/C4
Clinical picture	*Palpable purpura on buttocks/lower-limb extensors + arthritis + colicky abdominal pain* ^[1] Add renal haematuria/proteinuria for the classic tetrad; platelets/coagulation remain normal ^[2] Scrotal oedema can mimic torsion
Investigations	Diagnosis is mainly clinical; check CBC/platelets, coagulation, BP, urinalysis and RFT ^[2] Skin biopsy if atypical: leukocytoclastic vasculitis with IgA deposition Renal biopsy for AKI, nephritic/nephrotic disease or persistent proteinuria: mesangial IgA ± crescents ^[2]
Management	*Supportive care is the mainstay: hydration, rest, paracetamol; NSAID only without GI bleeding or nephritis ^[2] Steroids relieve severe abdominal/joint symptoms but do not alter overall course/prognosis* ^[2] Significant nephritis: ACEI/ARB; crescentic/RPGN requires nephrology-led immunosuppression
Complications	Intussusception is the commonest GI complication, usually ileo-ileal; bowel bleeding/perforation can occur ^[2] Persistent nephritis → CKD/ESRD; renal disease may appear months after rash CNS vasculitis/HTN complications and scrotal involvement are uncommon
Prevention / follow-up	*All patients need serial BP and urine dipstick follow-up—commonly up to 2 years* ^[2] Quantify persistent proteinuria, control BP/proteinuria with ACEI/ARB and escalate renal follow-up promptly
Exam traps	Palpable purpura + normal platelets/coagulation indicates vasculitis, not ITP/coagulopathy ^[2] IgAV/IgAN is synpharyngitic; PSGN follows infection after a latent interval and lowers C3 Steroids may mask perforation; worsening abdominal pain needs ultrasound/imaging Doppler: preserved/increased testicular flow in IgAV vs reduced/absent in torsion

References

^[1] Lecture slides: GC 053. Fingers turn white and blue.pdf (IgA vasculitis) ^[2] Senior notes: Adrian Lui Pediatrics Notes.pdf (HSP, pp. 460–461); MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (HSP, pp. 698–704); Maksim Surgery Notes.pdf (HSP follow-up)

IgA Vasculitis (Henoch-Schönlein Purpura)

IgA vasculitis (IgAV), historically known as Henoch-Schönlein purpura (HSP), is a systemic small vessel vasculitis characterised by the deposition of IgA1-dominant immune complexes in the walls of small vessels (predominantly capillaries, venules, and arterioles) ^[1]^[2]^[3].

Breaking down the name:

"IgA" = immunoglobulin A, the antibody class driving the disease
"Vasculitis" = "vas" (vessel) + "-itis" (inflammation) — inflammation of blood vessels
"Henoch" = Eduard Henoch (described the GI and renal involvement)
"Schönlein" = Johann Schönlein (described the association of purpura with arthritis)
"Purpura" = from Latin "purpura" (purple) — non-blanching purple skin lesions caused by extravasation of red blood cells

Per the 2012 revised Chapel Hill Consensus Conference (CHCC) nomenclature, the preferred term is now IgA vasculitis (IgAV) rather than HSP, to emphasize the pathogenic role of IgA ^[2]^[3].

"Vasculitis with IgA1-dominant immune deposits affecting small vessels (predominantly capillaries, venules, or arterioles). Often involves skin and gastrointestinal tract and frequently causes arthritis. Glomerulonephritis indistinguishable from IgA nephropathy may occur." — CHCC 2012 definition ^[2]^[3]

Key Distinction from IgA Nephropathy

IgA vasculitis and IgA nephropathy (IgAN/Berger disease) have IDENTICAL renal histopathology (mesangial IgA deposition). The difference is that IgAV is a systemic disease with extra-renal manifestations (palpable purpura, arthralgia, abdominal pain), while IgAN is renal-limited ^[2]^[4]^[5]. Some experts consider IgAN the renal-limited form of IgA vasculitis ^[5].

2. Epidemiology

Annual incidence: 3–27 per 100,000 children per year ^[4]^[6]
Most common systemic vasculitis in childhood ^[1]^[2]^[4]^[6]
90% of cases occur in the paediatric age group (aged 3–15 years) ^[4]^[6]
Can occur in adults, but less common and tends to be more severe (especially renal involvement → higher risk of ESRD) ^[6]

Feature	Detail
Sex	Male > Female (M:F = 1.2–1.8 : 1) ^[4]^[6]
Peak age of onset	6–7 years old (range 3–15 years) ^[4]^[6]
Race	More common in Caucasians and East Asians; relatively rare in Black populations
Seasonal variation	More common in winter and spring, unusual in summer months ^[4]^[6] — correlates with increased URTI incidence

Approximately 50% of cases are preceded by an upper respiratory tract infection (URTI) ^[4]^[6]
Hypersensitivity reaction to bacteria or viruses ^[1]
Occurs commonly in spring and after an URTI ^[1]
The seasonal and post-infectious pattern supports an immune-mediated pathogenesis triggered by mucosal infection

High Yield - Epidemiology

Children (2–10 years) are more commonly affected. Adults may also be affected ^[1]. When HSP occurs in adults, the renal prognosis is significantly worse. Intussusception is rare in adults but common in children ^[6].

3. Anatomy and Function of Affected Structures

IgAV primarily affects small blood vessels: capillaries, venules, and arterioles. Understanding the anatomy of these vessels explains the clinical manifestations:

Vessel	Structure	Why it matters in IgAV
Dermal capillaries & post-capillary venules	Thin-walled, fenestrated endothelium	IgA immune complex deposition → leukocytoclastic vasculitis → RBC extravasation → palpable purpura
Synovial capillaries	Richly vascularised joint capsule	Vasculitis → periarticular oedema and inflammation → arthralgia/arthritis
GI submucosal vessels	Dense submucosal vascular plexus (Meissner's plexus area)	Vasculitis → submucosal haemorrhage and oedema → abdominal pain, GI bleeding, intussusception
Glomerular capillaries (mesangium)	Specialised capillary tuft within Bowman's capsule	IgA deposition in mesangium → mesangial proliferation → glomerulonephritis
Scrotal vessels	Highly vascularised cremasteric and testicular coverings	Vasculitis → oedema/pain mimicking testicular torsion

IgA is the most abundantly produced immunoglobulin in the human body (mainly at mucosal surfaces). Two subclasses exist:

IgA1: predominant in serum; has a hinge region susceptible to abnormal O-glycosylation → key to pathogenesis of IgAV
IgA2: predominant in secretions; lacks the hinge region

IgA is produced mainly by mucosal-associated lymphoid tissue (MALT), including tonsillar and gut-associated lymphoid tissue (GALT). This explains why mucosal infections (URTI) are common triggers.

The glomerular mesangium is the connective tissue framework between capillary loops within the glomerulus. Mesangial cells:

Provide structural support
Have phagocytic function (clear immune complexes from the glomerular filtrate)
Express receptors for IgA (including the transferrin receptor CD71)

When overwhelmed by IgA immune complexes, mesangial cells proliferate and release pro-inflammatory cytokines and activate complement → mesangial proliferative glomerulonephritis.

4.1 Triggers and Risk Factors

The exact cause of IgAV remains unknown, but it is an immune-mediated process triggered by environmental exposures in a genetically predisposed individual.

Infectious Triggers (most important)

Trigger	Detail
URTI (most common)	~50% preceded by URTI within 1–3 weeks; includes Group A Streptococcus, Mycoplasma, adenovirus, parainfluenza, parvovirus B19, EBV
GI infections	Campylobacter, Helicobacter pylori, Yersinia
Other infections	Varicella, measles, hepatitis A/B, HIV

In Hong Kong, the high density of paediatric population in schools and the subtropical winter/spring season (with peaks of respiratory viral infections) contribute to clustering of cases.

Non-Infectious Triggers

Trigger	Examples
Drugs	Vancomycin, cefuroxime, clarithromycin, ACE inhibitors, NSAIDs, TNF inhibitors
Vaccines	Measles, typhoid, cholera, yellow fever (rare, temporal association)
Insect bites	Various arthropod bites
Food allergens	Rare trigger

Genetic Factors

Familial clustering reported (rare)
HLA associations: HLA-B35, HLA-DRB101, HLA-DRB111 (vary by ethnicity)
Complement gene polymorphisms (C4 null alleles)
In East Asian populations including Hong Kong Chinese, certain HLA alleles may predispose to IgAN/IgAV, though this is not routinely tested clinically

5. Pathophysiology

This is the crux of understanding IgAV. Think of it as a multi-hit model:

5.1 Step-by-Step Pathogenesis

A mucosal infection stimulates the mucosal immune system (MALT, tonsils, Peyer's patches)
In susceptible individuals, there is dysregulated B-cell switching favouring IgA1 production
The IgA1 produced is abnormally glycosylated — specifically, it is galactose-deficient at the hinge region O-glycan sites (galactose-deficient IgA1, Gd-IgA1)

Why does galactose deficiency matter? Because the exposed N-acetylgalactosamine (GalNAc) residues on Gd-IgA1 are recognized as neo-antigens by anti-glycan IgG and IgA antibodies, leading to formation of pathogenic immune complexes.

Gd-IgA1 self-aggregates (polymeric IgA)
Anti-Gd-IgA1 antibodies (IgG or IgA class) bind to form circulating immune complexes
These complexes are too large to be cleared efficiently by the hepatic asialoglycoprotein receptor and the mesangial/reticuloendothelial systems

Characteristic findings include leukocytoclastic vasculitis accompanied by IgA immune complexes within affected organs ^[6]
IgA-containing immune complexes deposit in:
- Dermal vessel walls → skin purpura
- GI submucosal vessels → abdominal symptoms
- Glomerular mesangium → nephritis (identical to IgA nephropathy histology)
- Synovial vessels → joint symptoms

Deposited IgA activates the alternative and lectin complement pathways (NOT the classical pathway — hence C3 may be low but C4 is usually normal, though in IgAV complement levels are typically normal)
Neutrophils are recruited → release lysosomal enzymes and reactive oxygen species
Leukocytoclastic vasculitis: "leuko" = white blood cell, "clastic" = broken → literally means vasculitis where neutrophils infiltrate and then fragment (nuclear dust/karyorrhexis) around small vessels
Vessel wall fibrinoid necrosis → increased vascular permeability → haemorrhage + oedema

Organ	Mechanism	Clinical Result
Skin	IgA deposition in dermal vessels → leukocytoclastic vasculitis → RBC extravasation	Palpable purpura (non-blanching because RBCs are in the tissues, not in dilated vessels)
Joints	Periarticular vessel vasculitis → oedema and inflammation	Arthralgia/arthritis
GI tract	Submucosal vessel vasculitis → oedema + haemorrhage → bowel wall thickening	Colicky abdominal pain, GI bleeding, intussusception
Kidney	IgA deposition in glomerular mesangium → mesangial proliferation → GN	Haematuria, proteinuria, nephritic/nephrotic syndrome
Scrotum	Vessel inflammation → oedema	Scrotal pain mimicking torsion

Why Palpable Purpura?

Purpura is "palpable" (raised) because the vasculitis causes an inflammatory infiltrate in the vessel wall and perivascular tissue, creating a palpable nodule. Simple thrombocytopenic purpura is flat because there's no inflammatory component — just passive leakage through intact but unsupported vessels.

HSP and IgA nephropathy have identical renal pathology ^[2]^[4]^[5]:

Mesangial IgA deposition (staghorn pattern on immunofluorescence)
Mesangial proliferation
Electron-dense deposits in mesangium

The only difference is that IgAV has systemic manifestations while IgAN is renal-limited. Some experts consider IgAN the renal-limited form of IgAV ^[5]. This shared pathogenesis explains why:

Both are triggered by mucosal infections
Both involve Gd-IgA1
Both can progress to crescentic GN and ESRD

6. Classification

IgAV is classified under immune complex-mediated small vessel vasculitis ^[2]^[3]:

Classification of primary vasculitis: IgA vasculitis (Henoch-Schönlein Purpura) is classified under medium/small vessel disease ^[1]

For paediatric IgAV, the validated classification criteria are:

Mandatory criterion:

Purpura or petechiae (predominantly lower limb) with at least one of:
1. Diffuse abdominal pain
2. Any biopsy showing predominant IgA deposition
3. Arthritis or arthralgia
4. Renal involvement (haematuria and/or proteinuria)

Sensitivity 100%, specificity 87%.

Age of onset ≤20 years
Palpable purpura
Acute abdominal pain (bowel angina)
Biopsy showing granulocytes in walls of arterioles/venules

≥2 of 4 criteria → sensitivity 87.1%, specificity 87.7%.

Severity	Features
Mild	Skin ± joints only; no GI or renal involvement
Moderate	GI involvement (pain, mild bleeding) without surgical complications
Severe	Severe GI complications (intussusception, perforation, massive bleeding) or significant renal disease (nephrotic syndrome, RPGN, AKI/CKD)

7. Clinical Features

Classical triad (from GC lecture): Acute onset / rapid resolution — (1) Palpable purpura, (2) Arthritis, (3) Abdominal pain ^[1]

However, the full clinical spectrum is a tetrad (as described in paediatric texts) ^[4]^[6]:

Palpable purpura (mandatory for diagnosis)
Arthralgia/arthritis
Abdominal pain
Renal disease

"FA GASP" mnemonic: Fever, Arthralgia, GN (glomerulonephritis), colicky Abdominal pain, Skin rash (must!), Periarticular edema ^[7]

The order of appearance is variable, but skin involvement usually comes first (in ~75% of cases, purpura is the presenting feature). In ~25%, abdominal or joint symptoms may precede the rash, making early diagnosis challenging.

7.2 Symptoms (with Pathophysiological Basis)

Symptom	Pathophysiological Basis
Non-blanching rash (purpura/petechiae)	IgA immune complex deposition in dermal vessels → leukocytoclastic vasculitis → vessel wall damage → RBC extravasation into dermis. Non-blanching because RBCs are extravascular (pressing doesn't push them back into vessels)
Initial erythematous macules/wheals that progress to purpura	Early phase: vasculitis causes endothelial activation and vasodilation (blanching). As vessel wall damage progresses → haemorrhage → non-blanching purpura
Pain/tenderness of skin lesions	Inflammation and oedema in perivascular tissue stimulates cutaneous nociceptors
Subcutaneous oedema (especially dependent and periorbital areas)	Increased vascular permeability from vasculitis → fluid leak into interstitium; gravity-dependent distribution

Distribution: Symmetrical, predominantly affecting buttocks and extensor surfaces of lower limbs ^[7]. This is because:

Dependent areas have higher hydrostatic pressure → more immune complex deposition
Gravity concentrates circulating immune complexes in lower extremity vessels
In young children who are not yet walking, the face and upper limbs may also be involved

Symptom	Pathophysiological Basis
Arthralgia (joint pain without swelling)	Vasculitis of synovial and periarticular vessels → perivascular inflammation → pain
Arthritis (joint swelling + pain)	More severe vasculitis → increased vascular permeability → synovial oedema and effusion
Periarticular oedema	Vasculitis-induced capillary leak in periarticular soft tissues

Characteristics:

Transient, migratory, non-deforming oligoarthritis ^[4]
Mainly large joints of the lower limbs (knees, ankles) ^[4]
Does NOT cause joint destruction or deformity (self-limiting inflammatory process, no pannus formation)
The joint symptoms often precede or accompany the rash

Symptom	Pathophysiological Basis
Colicky abdominal pain ^[7]	Vasculitis of GI submucosal vessels → submucosal haemorrhage and oedema → bowel wall thickening → stimulation of visceral pain fibres; intermittent spasm of inflamed bowel
Nausea/vomiting	Intestinal wall oedema → impaired motility; peritoneal irritation
Diarrhoea	Mucosal inflammation → impaired absorption and increased secretion
GI bleeding (haematemesis/melaena/haematochezia)	Mucosal vessel damage → erosion into GI lumen → overt bleeding
Intussusception ^[7]^[8]	Submucosal haemorrhage and oedema creates a "lead point" → peristalsis telescopes the oedematous segment into the adjacent normal bowel (usually ileo-ileal in HSP, not ileocolic)

Intussusception in HSP vs Idiopathic Intussusception

Idiopathic intussusception (commonest in infants 6–36 months) is usually ileocolic with hypertrophied Peyer's patches as the lead point
HSP-related intussusception is more commonly ileo-ileal (small bowel intussusception) because the lead point is submucosal haemorrhage/oedema
HSP is listed as a pathological lead point for intussusception ^[8]
Intussusception is rare in adults but common in children with HSP ^[6]

Symptom	Pathophysiological Basis
Haematuria (microscopic → gross)	IgA deposition in glomerular mesangium → mesangial proliferation → disruption of glomerular basement membrane → RBCs leak into urine
Proteinuria	Mesangial and podocyte injury → loss of glomerular charge/size selectivity barrier → protein leaks into urine
Oedema (periorbital, peripheral)	If nephrotic-range proteinuria → hypoalbuminaemia → reduced oncotic pressure → oedema
Oliguria	Severe GN → reduced GFR → decreased urine output
Hypertension	Renal inflammation → sodium and water retention; activation of RAAS
Scrotal pain/swelling	Vasculitis of cremasteric and testicular vessels → oedema and inflammation → can mimic testicular torsion (but normal ultrasound flow) ^[4]
Flank/loin pain	Renal capsule stretching from renal inflammation and oedema

Important - Scrotal Involvement

Scrotal swelling in a boy with HSP can mimic testicular torsion (a surgical emergency). The key differentiator is Doppler ultrasound: in HSP, blood flow to the testis is preserved (or even increased due to inflammation), whereas in torsion, flow is absent/reduced. Always image before rushing to theatre!

Symptom	Pathophysiological Basis
Headache	CNS vasculitis → perivascular inflammation
Seizures	Cerebral vasculitis → focal ischaemia or haemorrhage → cortical irritation
Intracranial haemorrhage	Vasculitis of CNS vessels → vessel wall necrosis → bleeding
Behavioural changes	CNS vasculitis → subtle ischaemic injury affecting frontal/temporal lobes

Symptom	Pathophysiological Basis
Low-grade fever	Systemic inflammation → IL-1, IL-6, TNF-α release → hypothalamic thermostat reset
Malaise/fatigue	Systemic cytokine release (especially IL-6) → sickness behaviour

7.3 Signs (with Pathophysiological Basis)

Sign	Description	Pathophysiology
Palpable purpura	Raised, non-blanching, 2–10 mm purple papules	IgA-mediated leukocytoclastic vasculitis → perivascular inflammatory infiltrate (makes it palpable) + RBC extravasation (makes it purple and non-blanching)
Petechiae	< 3 mm non-blanching red spots	Smaller foci of vessel damage
Ecchymoses	> 1 cm non-blanching bruise-like lesions	Confluent areas of vessel damage
Necrotic/bullous lesions	Vesicles or bullae overlying purpura (rare, severe)	Severe vessel wall necrosis → extensive subepidermal haemorrhage
Subcutaneous oedema	Non-pitting oedema of dependent areas (feet, legs) and periorbital regions	Increased vascular permeability → interstitial fluid accumulation

Distribution: symmetrical, predominantly affecting buttocks and extensors of lower limbs ^[7]. Upper extremity and trunk involvement is less common. In non-ambulatory infants, the face and upper limbs may be more affected.

Palpable purpura in patients with neither thrombocytopenia nor coagulopathy — this is a defining feature that distinguishes IgAV from other causes of purpura ^[6]

Sign	Description	Pathophysiology
Joint swelling	Periarticular soft tissue swelling, not true effusion usually	Vasculitis-induced capillary leak → periarticular oedema
Tenderness over joints	Pain on palpation of affected joints	Perivascular inflammation stimulating pain fibres
Preserved range of motion (early)	Unlike septic arthritis, movement is often possible	Non-destructive inflammatory process

Non-deforming: no pannus, no erosion, no cartilage destruction (cf. RA)
Migratory: shifts between joints over days
Lower limb predominance: knees and ankles most commonly affected

Sign	Description	Pathophysiology
Abdominal tenderness	Diffuse or periumbilical tenderness	Submucosal inflammation stimulates visceral afferents
Guarding/rigidity (if complications)	Suggests peritonitis from perforation	Transmural bowel wall necrosis → perforation → peritoneal contamination
Palpable mass (if intussusception)	Sausage-shaped mass, usually RLQ to RUQ	Telescoped bowel segment
Absent bowel sounds	Ileus from severe bowel wall oedema	Impaired myenteric plexus function from oedema/ischaemia
Bloody stool (PR)	Frank blood or melaena	Mucosal haemorrhage into GI lumen

Sign	Description	Pathophysiology
Hypertension	BP > 95th percentile for age/sex/height in children	Sodium/water retention from GN + RAAS activation
Peripheral oedema	Pitting oedema of ankles, periorbital	Nephrotic syndrome → hypoalbuminaemia → reduced intravascular oncotic pressure
Ascites (rare, severe nephrotic)	Abdominal distension with shifting dullness	Severe hypoalbuminaemia → third-spacing

Sign	Description	Pathophysiology
Scrotal swelling	Unilateral or bilateral scrotal oedema	Vasculitis of cremasteric/scrotal vessels
Normal cremasteric reflex	Reflex intact (cf. absent in torsion)	Spermatic cord not twisted
Normal Doppler flow	Blood flow preserved on USS	No mechanical obstruction to blood supply

A typical clinical course:

Prodrome (1–3 weeks before): URTI with cough, coryza, sore throat
Acute phase (days to weeks):
- Skin rash appears first in ~75% (sometimes preceded by joint or abdominal pain)
- Joint symptoms: often concurrent with or shortly after rash
- Abdominal symptoms: often within 1 week of rash onset
- Renal involvement: may appear weeks to months after initial presentation (hence the need for prolonged monitoring)
Resolution (usually 4–6 weeks): self-limiting in most children
Relapses: occur in ~33% of cases, usually milder than initial episode

Feature	Children	Adults
Incidence	90% of all cases	10% of all cases
Renal involvement	~50%, usually mild	More frequent, more severe, higher risk of ESRD
Intussusception	Common	Rare
Rash	Classic distribution	May be more extensive/atypical
Prognosis	Excellent (self-limiting in ~90%)	Guarded (significant renal morbidity)

System	Frequency	Key Features	Pathophysiological Basis
Skin	~100%	Palpable purpura (buttocks, LL extensors); subcutaneous oedema	Leukocytoclastic vasculitis of dermal vessels
Musculoskeletal	~75%	Transient migratory oligoarthritis (knees, ankles); periarticular oedema	Vasculitis of synovial/periarticular vessels
GI	~80%	Colicky abdominal pain; GI bleeding; intussusception (ileo-ileal)	Submucosal vessel vasculitis → haemorrhage + oedema
Renal	~50%	Haematuria, proteinuria, HTN, nephritic/nephrotic syndrome	Mesangial IgA deposition → proliferative GN
Scrotal	~15% boys	Swelling/pain mimicking torsion (normal US)	Cremasteric vessel vasculitis
CNS	< 5%	Headache, seizures, ICH, behavioural changes	Cerebral vessel vasculitis

High Yield Summary

Definition: IgAV (HSP) is an immune complex-mediated small vessel vasculitis with IgA1-dominant deposits affecting capillaries, venules, and arterioles ^[1]^[2]^[3]
Epidemiology: Most common systemic vasculitis in childhood; peak age 6–7 years; M > F; more common in winter/spring, often after URTI ^[1]^[4]^[6]
Pathogenesis: Mucosal infection → aberrant galactose-deficient IgA1 production → immune complex formation → deposition in small vessel walls → leukocytoclastic vasculitis with IgA-containing immune complexes → complement activation + neutrophil recruitment → vessel wall damage → end-organ injury ^[4]^[6]
Clinical tetrad: (1) Palpable purpura (must be present), (2) Arthralgia/arthritis, (3) Abdominal pain, (4) Renal disease ^[1]^[4]^[6]^[7]
Classical triad from GC lecture: Acute onset / rapid resolution — Palpable purpura, Arthritis, Abdominal pain ^[1]
Key pathology point: IgAV and IgA nephropathy have IDENTICAL renal histopathology (mesangial IgA deposition); IgAV is the systemic form, IgAN is renal-limited ^[2]^[4]^[5]
Palpable purpura is palpable because of inflammatory infiltrate (not just RBC extravasation) — distinguishes from thrombocytopenic purpura which is flat
Intussusception in HSP is usually ileo-ileal (not ileocolic) and the submucosal haemorrhage acts as a pathological lead point ^[8]
Normal platelets and coagulation — purpura occurs despite normal haemostatic parameters ^[6]
Adults have worse renal prognosis than children

Active Recall - IgA Vasculitis (HSP)

^[1] Lecture slides: GC 053. Fingers turn white and blue.pdf (slides on IgA vasculitis / HSP, pp. 79–80, 95) ^[2] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (pp. 1764, 1766, 1768 — Chapel Hill classification, vasculitis subtypes) ^[3] Senior notes: Ryan Ho Rheumatology.pdf (pp. 93–94 — vasculitis classification and clinical features) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 460 — HSP overview) ^[5] Senior notes: Ryan Ho Urogenital.pdf (pp. 58–59 — IgA nephropathy and relationship with HSP) ^[6] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 698 — HSP paediatric features) ^[7] Senior notes: Maksim Medicine Notes.pdf (pp. 233, 334 — HSP in nephrology and rheumatology context) ^[8] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p. 1045 — intussusception and HSP as pathological lead point)

Differential Diagnosis of IgA Vasculitis (Henoch-Schönlein Purpura)

The differential diagnosis of IgAV must be approached systematically because the condition presents with a constellation of features (purpura, joint pain, abdominal pain, renal disease) — and each of these features individually has a broad differential. The key clinical challenge is: a child (or adult) presents with purpura ± arthralgia ± abdominal pain ± haematuria — is this HSP, or something else?

The approach is organised by:

Presenting complaint — what brought the patient in (usually the rash)
Organ-system overlap — conditions that mimic specific organ involvement of IgAV

The first and most critical branch point is whether the purpura is palpable (raised) or non-palpable (flat) ^[9]^[10]^[11].

Differentiating features from thrombocytopenic purpura: Raised, papular and sometimes tender ^[12]

This is because:

Palpable purpura = inflammatory infiltrate in and around the vessel wall (vasculitis or septic emboli) → the inflammation creates a palpable nodule
Non-palpable purpura = passive extravasation of RBCs through unsupported (thrombocytopenia) or fragile (scurvy, steroids) vessel walls, with no inflammatory component

High Yield – Palpable vs Non-Palpable Purpura

Palpable purpura is caused by: (1) Systemic vasculitis (tender), (2) Bacteraemia (non-tender) ^[10]. This single examination finding instantly narrows the differential from dozens of causes to a handful of vasculitides and infections. IgAV purpura is palpable because it is inflammatory (leukocytoclastic vasculitis), and it occurs in patients with neither thrombocytopenia nor coagulopathy ^[6].

2. Differential Diagnosis of Purpura (Comprehensive)

This is organised by the classic haematology framework: vessel → platelet → coagulation ^[10]^[11].

Condition	Key Distinguishing Features from IgAV	Why it mimics IgAV
Infective endocarditis (IE) [6a]	Persistent fever, new/changing murmur, splinter haemorrhages, Janeway lesions, Osler nodes, +ve blood cultures; renal involvement from septic emboli or IC-GN	Palpable purpura + GN + arthralgia
Meningococcaemia [6a]	Life-threatening condition that cannot be missed [6a]; rapid onset, high fever, shock, petechiae/purpura progressing rapidly, often non-palpable initially becoming palpable; meningeal signs; positive blood/CSF cultures	Purpura in a febrile child — but much more acutely unwell, rapidly deteriorating
ANCA-associated vasculitis (GPA, EGPA, MPA) [6a]	Older age group (adults typically); GPA: sinusitis + pulmonary infiltrates + nephritis; EGPA: asthma + eosinophilia; MPA: pulmonary-renal syndrome; ANCA positive (c-ANCA/PR3 for GPA, p-ANCA/MPO for MPA/EGPA)	Palpable purpura + GN + constitutional symptoms
Cryoglobulinaemic vasculitis ^[7]	Meltzer's triad: palpable purpura + arthralgia + weakness/myalgia; associated with HCV/HIV/HBV; digital ischaemia, livedo reticularis, Raynaud's; ↓C4, +ve RF (Type 2), cryocrit elevated	Palpable purpura + arthralgia + GN — but has ↓C4, +ve cryoglobulins, and HCV link
SLE vasculitis ^[12]	Purpuric skin rash in SLE can be from thrombocytopenia OR leucocytoclastic vasculitis ^[12]; malar rash, photosensitivity, oral ulcers, serositis, cytopenias, +ve ANA/anti-dsDNA, ↓C3/C4	Palpable purpura + arthritis + GN — but typically older (young women), multi-system with characteristic autoantibodies
Kawasaki disease ^[3]	Age < 5 years; ≥5 days fever + conjunctivitis + oral changes + rash (polymorphous, NOT typically purpuric) + extremity changes + cervical lymphadenopathy; coronary artery aneurysms	Fever + rash + arthralgia in a child — but rash is NOT purpuric and distribution differs
Polyarteritis nodosa (PAN) ^[1]	Medium vessel vasculitis; viral hepatitis B related ^[1]; livedo reticularis, subcutaneous nodules, digital infarcts, mesenteric aneurysms, testicular involvement; ANCA usually negative; no GN (medium vessel, not glomerular capillary)	Abdominal pain + testicular pain + rash — but rash is livedo/nodular not purpuric; NO GN
Hypersensitivity vasculitis (drug-induced)	Temporal relationship with drug exposure; palpable purpura predominantly LL; often no renal or GI involvement; resolves on drug withdrawal	Palpable purpura on LL — but no systemic involvement and clear drug temporal link

High Yield – Complement Levels Help Narrow the DDx

Serum complement level is important in helping narrow the differential diagnosis ^[5]^[13]:

↓C3/C4 generally indicates IC-mediated GN: MPGN, PSGN, lupus, cryoglobulinaemia, IE, shunt nephritis ^[5]^[13]
Normal C3/C4 generally indicates non-IC-mediated GN (except IgAN): PAN, Goodpasture, HSP/IgAN, ANCA-related renal vasculitis ^[5]^[13]

So HSP/IgAN characteristically has NORMAL complement despite being immune complex-mediated. This is because IgA activates complement via the alternative/lectin pathways (which do not consume C4) and the activation is relatively localised to the tissue rather than systemic. This is a key distinguishing point from lupus nephritis and PSGN.

These present with flat, non-palpable petechiae/purpura and LOW platelet count — fundamentally different from IgAV where platelets are NORMAL ^[4][6a].

Condition	Key Distinguishing Features	Why it enters the DDx
Immune thrombocytopenic purpura (ITP)	Isolated thrombocytopenia (< 100 × 10⁹/L); no systemic features; mucocutaneous bleeding pattern; often post-viral in children; purpura is FLAT	Purpura in a child post-URTI — but flat, widespread, and low platelets
Haemolytic uraemic syndrome (HUS)	Triad: microangiopathic haemolytic anaemia + thrombocytopenia + AKI; often post-diarrhoeal (E. coli O157:H7); schistocytes on blood film	Purpura + renal impairment in a child — but has MAHA, low platelets, preceding bloody diarrhoea
Thrombotic thrombocytopenic purpura (TTP)	Pentad: MAHA + thrombocytopenia + renal impairment + neurological features + fever; ADAMTS13 deficiency; rare in children	Purpura + renal involvement + fever — but has MAHA, very low platelets, neurological signs
Disseminated intravascular coagulopathy (DIC)	Underlying trigger (sepsis, malignancy, trauma); ↑PT, ↑aPTT, ↓fibrinogen, ↑D-dimer, ↓platelets, schistocytes	Purpura + bleeding — but abnormal coagulation and underlying critical illness
Leukaemia	Pancytopenia (anaemia, neutropenia, thrombocytopenia); hepatosplenomegaly, lymphadenopathy; blasts on blood film/BM	Purpura in a child — but pancytopenia, constitutional symptoms, organomegaly
Drug-induced thrombocytopenia	Temporal relationship with offending drug (e.g. heparin, ibuprofen, ampicillin); resolves on drug withdrawal	Purpura after drug exposure — but low platelets

The critical bedside test: check the platelet count. In IgAV, platelets are normal (or even mildly elevated as an acute-phase reactant). If platelets are low, IgAV is essentially excluded and you are in thrombocytopenic territory ^[4][6a].

Condition	Key Distinguishing Features	Why it enters the DDx
Von Willebrand disease (vWD)	Mucocutaneous bleeding (epistaxis, menorrhagia, post-procedural); ↑bleeding time, ↓vWF:Ag, ↓vWF:RCo; AD inheritance (most types)	Bleeding/bruising — but NO purpuric rash, normal platelets or mildly ↓, abnormal vWF studies
Haemophilia A/B	Haemarthroses, deep muscle bleeds, post-traumatic bleeding; X-linked; isolated ↑aPTT; ↓Factor VIII (A) or IX (B)	Deep bleeding/bruising — but pattern is haemarthrosis not purpura; coagulation-type not platelet-type

Condition	Key Distinguishing Features	Why it enters the DDx
Scurvy (vitamin C deficiency)	Perifollicular purpura (classically LL), corkscrew hairs, swollen gums, poor wound healing; dietary history	Purpura on LL — but perifollicular pattern, dietary deficiency, no systemic vasculitis features
Ehlers-Danlos syndrome	Easy bruising, skin hyperextensibility, joint hypermobility; connective tissue disorder	Easy bruising — but no palpable purpura, characteristic skin/joint findings
Senile/steroid purpura	Elderly patients or chronic steroid use; flat purpura on sun-exposed skin (forearms); no systemic features	Purpura — but flat, atrophic skin, no vasculitis features

3. Differential Diagnosis by Organ-System Overlap

When IgAV presents predominantly with haematuria and proteinuria, the differential is that of nephritic syndrome ^[5]^[13]^[14]:

Condition	Complement	URTI Timing	Key Distinguishing Feature
IgAV (HSP)	Normal C3/C4	Concurrent with URTI	Palpable purpura + arthralgia + abdominal pain
IgA nephropathy	Normal C3/C4	Synpharyngitic (concurrent with URTI)	Identical renal pathology to HSP but NO extra-renal features ^[2]^[5]
Post-streptococcal GN (PSGN)	↓C3 (normalises by 4 weeks)	7–10 days AFTER strep throat/impetigo ^[7]	Latent period (7–10 days); periorbital oedema; ↑ASOT; NO purpura
Lupus nephritis	↓C3/C4	No relationship	Multi-system: malar rash, photosensitivity, serositis; +ve ANA/anti-dsDNA
ANCA-associated GN	Normal C3/C4	No relationship	RPGN; pulmonary haemorrhage (MPA); ENT disease (GPA); +ve ANCA
Anti-GBM disease	Normal C3/C4	No relationship	RPGN + pulmonary haemorrhage; +ve anti-GBM antibody; linear IF
MPGN	↓C3 ± ↓C4	May have episodic haematuria	Chronic/slowly progressive; associated with HCV, autoimmune diseases
Cryoglobulinaemic GN	↓C4 (characteristic)	No relationship	HCV association; Meltzer's triad; +ve cryocrit, +ve RF

Relationship with URTI is key: URTI 7–10 days before → think PSGN; concurrent with URTI → think IgAN/IgAV ^[5]^[13]

Differential diagnosis of nephritic syndrome by IF pattern ^[14]:

Pauci-immune (negative IF): ANCA-associated GN (GPA, EGPA, MPA)
Linear IF deposits: Anti-GBM disease (Goodpasture syndrome)
Granular IF deposits with normal C3: IgA nephropathy / IgAV
Granular IF deposits with ↓C3: SLE, IE, cryoglobulinaemia, MPGN

When IgAV presents predominantly with acute abdominal pain in a child ^[8]:

Condition	Key Distinguishing Features
Acute appendicitis	RIF pain (migrating from periumbilical), rebound tenderness, McBurney's point; no purpura; ↑WBC
Mesenteric adenitis	Viral prodrome, diffuse/periumbilical pain, USG shows mesenteric lymphadenopathy; no purpura
Intussusception (idiopathic)	Episodic colicky pain, vomiting, red-currant jelly stools, sausage-shaped mass; age 6–36 months; USG target sign
Meckel's diverticulitis	Painless PR bleeding (99mTc pertechnetate scan); or presents like appendicitis
Gastroenteritis	Diarrhoea and vomiting, no purpura, contact history
DKA	Abdominal pain + vomiting + Kussmaul breathing + hyperglycaemia + ketonuria

Paediatric surgical abdomen DDx: GI (IO, appendicitis, mesenteric adenitis, Meckel's, intussusception), GU (UTI, testicular torsion), Vascular (HSP), Medical (DKA, GE) ^[8]

HSP Abdominal Pain vs Intussusception

A child with known HSP who develops severe colicky abdominal pain may have either: (1) simple submucosal haemorrhage/oedema from vasculitis, or (2) intussusception as a complication of HSP. Abdominal pain in HSP: intestinal vasculitis vs intussusception — differentiated by USG ^[8]. Always perform USG abdomen to look for intussusception (target/doughnut sign) in any HSP child with significant abdominal symptoms.

Condition	Key Distinguishing Features
Testicular torsion	Sudden onset, severe pain, high-riding testis, absent cremasteric reflex, absent/reduced Doppler flow on USS — SURGICAL EMERGENCY
IgAV scrotal involvement	In context of purpura elsewhere; normal or increased Doppler flow; cremasteric reflex preserved
Epididymo-orchitis	Gradual onset, tender epididymis, positive Prehn's sign (pain relief on elevation), may have pyuria
Torsion of appendix testis	"Blue dot sign" on transillumination; localised tenderness at upper pole
Incarcerated inguinal hernia	Cannot get above the swelling; irreducible mass in groin/scrotum; obstructive symptoms

Differential diagnosis of scrotal pain: testicular torsion, torsion of appendix testis/epididymis, epididymitis, orchitis, incarcerated inguinal hernia, HSP, Fournier's gangrene, trauma ^[15]

Petechial/purpuric rash differential [6b]:

Category	Conditions
Infection	Meningococcal infection, infective endocarditis, enterovirus
Haematological	Thrombocytopenia (ITP, leukaemia, DIC, HUS, TTP)
Vasculitis	Henoch-Schönlein purpura, Kawasaki disease
Autoimmune	SLE

The following table summarises the "first-pass" laboratory features that help distinguish IgAV from its main mimics:

Investigation	IgAV (HSP)	ITP	Meningococcaemia	SLE	PSGN	ANCA vasculitis
Platelets	Normal	↓↓	↓ (± DIC)	↓ (immune)	Normal	Normal
Coagulation	Normal	Normal	Deranged (DIC)	Normal/variable	Normal	Normal
C3/C4	Normal	Normal	Normal	↓↓	↓C3	Normal
Serum IgA	↑ in ~50%	Normal	Normal	Normal	Normal	Normal
ANCA	Negative	Negative	Negative	Negative	Negative	Positive
ANA/anti-dsDNA	Negative	Negative	Negative	Positive	Negative	Negative
ASOT	May be ↑ (trigger)	Normal	Normal	Normal	↑↑	Normal
Blood culture	Negative	Negative	Positive	Negative	Negative	Negative
Skin biopsy	Leukocytoclastic vasculitis + IgA deposition	Non-specific	Gram-negative diplococci	Leukocytoclastic vasculitis ± immune complex	N/A	Necrotising vasculitis, pauci-immune

Think of it in three steps:

Step 1: Is the purpura palpable?

Yes → vasculitis or infection (consider IgAV, other vasculitides, IE, meningococcaemia)
No → platelet disorder, coagulopathy, or vessel fragility

Step 2: Are platelets and coagulation normal?

Yes → strongly favours IgAV (purpura with neither thrombocytopenia nor coagulopathy ^[6])
No → consider ITP, DIC, TTP/HUS, leukaemia

Step 3: What is the complement level?

Normal C3/C4 → IgAV/IgAN, ANCA vasculitis, anti-GBM disease
↓C3 ± ↓C4 → PSGN, lupus nephritis, MPGN, cryoglobulinaemia, IE

High Yield Summary — Differential Diagnosis

Palpable purpura = vasculitis or bacteraemia ^[10]. IgAV purpura is raised, papular, and sometimes tender — this distinguishes it from flat thrombocytopenic purpura ^[12]
IgAV has NORMAL platelets and NORMAL coagulation — this is a defining criterion ^[4]^[6]
IgAV has NORMAL complement (C3/C4) despite being immune-complex mediated — key differentiator from PSGN (↓C3), lupus (↓C3/C4), and cryoglobulinaemia (↓C4) ^[5]^[13]^[14]
IgA nephropathy has identical renal histopathology to IgAV — the difference is the presence of extra-renal manifestations (purpura, arthralgia, abdominal pain) ^[2]^[5]
URTI timing: concurrent → IgAV/IgAN; 7–10 days after → PSGN ^[5]^[13]
Meningococcaemia is a life-threatening condition that cannot be missed [6a] — a febrile child with rapidly progressive purpura needs urgent blood cultures and empiric antibiotics before any other workup
The three "must-not-miss" diagnoses when a child presents with purpura: (1) Meningococcaemia, (2) Leukaemia (pancytopenia), (3) NAI/child abuse (trauma pattern)

Active Recall - DDx of IgA Vasculitis

References

^[1] Lecture slides: GC 053. Fingers turn white and blue.pdf (slides on vasculitic syndromes, classification of primary vasculitis, IgA vasculitis) ^[2] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (pp. 997, 1764 — IgA nephropathy vs HSP, Chapel Hill classification) ^[3] Senior notes: Ryan Ho Rheumatology.pdf (pp. 93–94 — vasculitis classification and clinical features) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 460 — HSP overview) ^[5] Senior notes: Ryan Ho Urogenital.pdf (pp. 59, 63 — IgA nephropathy DDx and nephritic syndrome evaluation) ^[6] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 698 ^[6], p. 699 [6a], p. 86 [6b] — HSP overview, DDx of purpura, fever and rash DDx) ^[7] Senior notes: Maksim Medicine Notes.pdf (pp. 233, 334 — HSP in nephrology, cryoglobulinaemia) ^[8] Senior notes: Maksim Surgery Notes.pdf (p. 336 — paediatric surgical abdomen DDx, HSP features and USG) ^[9] Senior notes: Maksim Medicine Notes.pdf (p. 160 — approach to petechiae/purpura, palpable vs non-palpable) ^[10] Senior notes: Ryan Ho Haemtology.pdf (p. 5 — causes of petechiae, palpable purpura) ^[11] Senior notes: Ryan Ho Haemtology.pdf (p. 113 — classification of bleeding disorders by site of defect) ^[12] Lecture slides: GC 046. Facial rash and painful fingers_SLE.pdf (p. 30 — SLE purpuric rash, differentiating from thrombocytopenic purpura) ^[13] Senior notes: Ryan Ho Fundamentals.pdf (p. 360 — nephritic syndrome evaluation, complement levels in DDx) ^[14] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 421 — DDx of GN by IF pattern) ^[15] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p. 1107 — DDx of scrotal pain)

Diagnostic Criteria, Algorithm, and Investigations for IgA Vasculitis (HSP)

Diagnosis of HSP is largely clinical. NO laboratory findings are diagnostic of HSP ^[6]

This is the single most important principle to internalise. Unlike many rheumatological conditions, there is no specific blood test, autoantibody, or biomarker that definitively confirms IgAV. The diagnosis is made by recognising the clinical pattern — a child (or adult) with palpable purpura in the context of arthralgia, abdominal pain, and/or renal involvement, with normal platelets and normal coagulation.

Laboratory and histological investigations serve two purposes:

Exclusion of dangerous mimics (meningococcaemia, leukaemia, ITP, SLE, ANCA vasculitis)
Assessment of organ damage severity (especially renal involvement, which determines long-term prognosis)

2. Classification / Diagnostic Criteria

Three sets of criteria exist. Understand when to use each and what they cover.

This is the validated paediatric classification criteria, and the one most relevant for HKUMed exams.

Component	Detail
Mandatory criterion	Purpura or petechiae (predominantly lower limb distribution) with normal platelets and coagulation
Plus ≥1 of the following:
1. Diffuse abdominal pain	Acute onset, colicky
2. Any biopsy showing predominant IgA deposition	Skin or renal biopsy
3. Arthritis or arthralgia	Acute, any joint
4. Renal involvement	Haematuria and/or proteinuria

Sensitivity: 100%
Specificity: 87%

Why must purpura be present? Because skin rash (must!) is the defining feature ^[7]. Without purpura, you cannot classify a patient as having IgAV — you would need to consider other diagnoses (IgA nephropathy if renal-only, other vasculitides, etc.).

"FA GASP": Fever, Arthralgia, GN, colicky Abdominal pain, Skin rash (must!), Periarticular edema ^[7]

Criterion	Detail
1. Age of onset ≤20 years	Distinguishes from adult-onset vasculitides
2. Palpable purpura	Non-blanching, raised
3. Acute abdominal pain	Bowel angina, diffuse
4. Biopsy showing granulocytes in arteriolar/venular walls	Leukocytoclastic vasculitis

≥2 of 4 criteria → Sensitivity 87.1%, Specificity 87.7%.

Note: The ACR criteria are classification criteria (designed to distinguish IgAV from other vasculitides in research), not diagnostic criteria per se. They are less commonly used in paediatric practice.

"Vasculitis with IgA1-dominant immune deposits affecting small vessels (predominantly capillaries, venules, or arterioles). Often involves skin and gastrointestinal tract and frequently causes arthritis. Glomerulonephritis indistinguishable from IgA nephropathy may occur." ^[2]

This is a pathological definition — it tells you what the disease IS, not how to diagnose it at the bedside.

Criteria vs Diagnosis

A common student mistake: classification criteria are not the same as diagnostic criteria. Classification criteria are designed for research homogeneity (high specificity). In clinical practice, you may diagnose IgAV even if not all criteria are met, based on clinical judgment. Conversely, meeting criteria doesn't exclude coexisting conditions.

3. Diagnostic Algorithm

The diagnosis is clinically obvious and requires minimal investigation when you see:

A child aged 3–15 years
With palpable purpura on buttocks and lower limbs
Preceded by URTI
With arthralgia and/or abdominal pain
With normal platelets and coagulation

In this classic scenario, the role of investigations is to:

Confirm normal platelets/coagulation (exclude thrombocytopenia/coagulopathy)
Screen for renal involvement (urinalysis, RFT)
Assess for GI complications (USG if significant abdominal pain)

Atypical scenarios requiring more extensive workup:

Adult presentation (consider ANCA vasculitis, cryoglobulinaemia, SLE more seriously)
Purpura absent at presentation (joint or abdominal pain precedes rash in ~25%)
Atypical rash distribution (upper body, face)
Severe renal involvement at onset (need to differentiate from RPGN of other causes)
Persistent/chronic course (> 3 months — consider other systemic vasculitides)

4. Investigation Modalities — Systematic

Investigations are organised into: (A) Bedside, (B) Blood tests, (C) Urine, (D) Imaging, (E) Histology.

Investigation	Purpose	Key Findings in IgAV	Interpretation/Why
Blood pressure (BP) measurement ^[6]	Screen for hypertension from GN	May be elevated	GN → Na⁺/H₂O retention + RAAS activation → HTN. Important to document baseline and monitor serially
Skin examination	Characterise rash	Symmetrical palpable purpura, buttocks and LL extensors	Distribution + palpability points to vasculitis not thrombocytopenia
Urine dipstick	Rapid screen for haematuria/proteinuria	Blood +, Protein +	Suggests glomerular involvement; requires formal urinalysis
Stool occult blood	Screen for GI bleeding	May be positive	Submucosal haemorrhage → occult or frank GI blood loss

4.2 Blood Tests

Investigation	Expected in IgAV	Abnormal → Consider	Why Ordered
CBC with differential ^[4]^[6]	Normochromic or microcytic anaemia (from GI blood loss); leukocytosis (if preceding bacterial infection); NORMAL platelets ^[6]	↓↓Platelets → ITP, DIC, TTP/HUS, leukaemia; Blasts → leukaemia; Schistocytes → TMA	Normal platelet required to confirm purpura is not related to thrombocytopenia ^[6]. This is the single most important "rule-out" test
Clotting profile (PT, aPTT, fibrinogen) ^[4]^[6]	Normal coagulation parameters ^[6]	Deranged → DIC, coagulopathy, liver disease	To confirm purpura is not related to coagulopathy ^[6]
Blood film	Usually unremarkable	Schistocytes → TMA; Blasts → leukaemia	Mandatory when thrombocytopenia or anaemia detected

The Two 'Rule-Out' Tests

Normal platelet + normal clotting = purpura is vasculitic, not haemostatic ^[4]^[6]. These two simple tests instantly narrow the differential from the entire universe of purpura causes to the subset of vasculitides and bacteraemia. They should be sent on every patient presenting with purpura.

Investigation	Expected in IgAV	Clinical Significance
RFT (urea, creatinine, eGFR) ^[4]^[6]	Usually normal; ↑Cr if significant GN	Serum creatinine to evaluate for renal impairment ^[6]. Documents baseline and degree of renal damage. Rising Cr → consider renal biopsy
LFT (albumin) ^[4]^[6]	Hypoalbuminaemia can occur due to renal or intestinal protein loss ^[6]	Low albumin reflects: (1) nephrotic-range proteinuria (renal loss), or (2) protein-losing enteropathy (GI mucosal damage)
ESR and CRP ^[4]^[6]	↑ ESR and CRP level ^[6]	Non-specific inflammatory markers; confirms systemic inflammation. Useful for monitoring disease activity

Investigation	Expected in IgAV	If Abnormal → Consider	Rationale
Serum complement C3/C4 ^[4]^[6]	Expect C3 to be NORMAL in HSP ^[6]	↓C3 → PSGN, MPGN; ↓C3 + ↓C4 → SLE, cryoglobulinaemia	Serum complement level: important in helping narrow the differential diagnosis ^[5]^[13]. IgA activates complement locally via alternative/lectin pathways (not classical) → systemic complement usually normal
Serum IgGAM (immunoglobulins) ^[4]^[6]	Serum IgA is often elevated in 50–70% of patients ^[6]	Supports diagnosis but not specific (also elevated in IgAN, liver disease, coeliac disease)	↑IgA reflects the aberrant IgA1 immune response driving the disease. But 30–50% have normal IgA, so a normal level does NOT exclude IgAV
ANA, anti-dsDNA ^[4]^[6]	Negative	Positive → SLE	To differentiate SLE ^[6]
ANCA and subtypes ^[4]^[6]	Negative	c-ANCA/anti-PR3 → GPA; p-ANCA/anti-MPO → MPA/EGPA	ANCA to differentiate from ANCA-associated vasculitis ^[6]
ASOT titre ^[4]^[6]	May be elevated (if preceding strep infection triggered HSP)	Elevated → confirms streptococcal trigger	Usually performed to confirm preceding Streptococcal infection ^[6]. Does NOT mean the patient has PSGN — timing matters (concurrent = IgAV; 7–10 days after = PSGN)
Anti-GBM antibody	Negative	Positive → anti-GBM disease / Goodpasture syndrome	Only if RPGN or pulmonary haemorrhage suspected ^[13]
Cryocrit	Negative	Elevated → cryoglobulinaemic vasculitis	Only if HCV history or ↓C4 or clinical suspicion ^[13]
Blood culture	Negative	Positive → IE, meningococcaemia	If persistent fever or haemodynamic instability ^[13]

Immune complex diseases classified by complement and IF pattern ^[16]^[14]:

Complement Level	Renal-Limited	Systemic
Normal C3	IgA nephropathy	Henoch-Schönlein purpura (HSP)
↓C3	Infection-related GN (Staph, Strep/PSGN), MPGN	SLE, Infective endocarditis, Cryoglobulinaemia

This table is directly from the senior notes and GC teaching ^[16]^[14]. It is extremely high yield for exams.

IF (Immunofluorescence) pattern most helpful for diagnosis ^[13]:

Pauci-immune (minimal staining): ANCA-associated vasculitis
Linear staining: Anti-GBM disease
Granular staining: Immune complex disease (IgAV, IgAN, PSGN, lupus, cryoglobulinaemia)

Finding	Significance	Pathophysiology
Microscopic or macroscopic haematuria ^[6]	Glomerular involvement	IgA deposition → mesangial proliferation → GBM disruption → RBCs enter urine
Proteinuria ^[6]	Glomerular damage severity	Podocyte/mesangial injury → loss of size/charge selectivity barrier
Red cell casts or other cellular casts ^[6]	Confirms GLOMERULAR origin of haematuria (not lower urinary tract)	RBCs become enmeshed in Tamm-Horsfall protein as they traverse the tubule → cylindrical casts
Dysmorphic RBCs	Glomerular haematuria	RBCs squeezed through damaged GBM → distorted shape
Urine protein:creatinine ratio (UPCR)	Quantifies proteinuria	Spot ratio correlates with 24-hour urine protein; > 200 mg/mmol approximates nephrotic range

Urinalysis is both diagnostic (confirms renal involvement) and prognostic (persistent proteinuria > 1 month is an indication for renal biopsy). Serial urinalysis is the cornerstone of long-term follow-up.

Modality	Indication	Key Findings	Interpretation
USG abdomen ^[6]^[8]	Significant abdominal symptoms	Increased bowel wall thickness (oedema), haematoma, peritoneal fluid, intussusception ^[6]	Abdominal pain: intestinal vasculitis vs intussusception — differentiated by USG ^[8]. Target/doughnut sign → intussusception. Bowel wall thickening alone → vasculitic enteropathy
USG testes (with Doppler) ^[6]	Scrotal pain/swelling in boys	Normal or increased flow in HSP; decreased flow in testicular torsion ^[6]	Critically distinguishes HSP scrotal involvement from testicular torsion (surgical emergency)
AXR ^[6]	Suspected obstruction or ileus	Dilated bowel with fluid levels consistent with decreased intestinal motility or obstruction ^[6]	May show features of mechanical obstruction (intussusception) or paralytic ileus
CXR	If cough/haemoptysis (rare in IgAV)	Usually normal in IgAV	Pulmonary infiltrates → consider ANCA vasculitis (GPA, MPA) or Goodpasture

When to Image the Abdomen

Not every child with HSP and mild tummy ache needs an USS. Image the abdomen when there is: (1) severe or worsening abdominal pain, (2) bilious vomiting (suggests obstruction), (3) bloody stools (red-currant jelly → intussusception), (4) palpable abdominal mass. The USS differentiates simple vasculitic bowel wall oedema (conservative management) from intussusception (may need reduction) ^[6]^[8].

4.5 Histology (Biopsy)

Aspect	Detail
Indication	Often unnecessary in typical HSP and reserved for atypical presentation ^[6] — e.g., unusual age, atypical distribution, no other HSP features, uncertain diagnosis
Technique	Sample the small blood vessels of superficial dermis is adequate ^[6]
Key findings	Classical leukocytoclastic vasculitis with IgA deposition which is pathognomonic [4a]^[6]
Histology detail	Inflammation of small blood vessels... most prominent in the postcapillary venules ^[6]; neutrophilic infiltrate with nuclear dust (karyorrhexis); fibrinoid necrosis of vessel walls; RBC extravasation
Direct IF	IgA deposition in vessel walls — this is the pathognomonic finding that confirms the diagnosis when clinical features are equivocal

"Leukocytoclastic" literally means "white cell breaking" — you see fragmented neutrophil nuclei (nuclear dust) around small vessels. This is the hallmark histological pattern of small vessel vasculitis.

Aspect	Detail
Indication	Often unnecessary in typical HSP and reserved for atypical presentation or prominent renal involvement ^[6]: (1) AKI, (2) Nephritic syndrome at presentation, (3) Nephrotic-range proteinuria or persistent proteinuria > 1 month ^[6]
Why not biopsy everyone?	Most children with HSP have mild, self-limiting renal involvement. Biopsy is invasive and carries procedural risks (bleeding, infection). Reserve for those where the biopsy result will change management
Key findings	Identical to IgA nephropathy ^[2]^[5]:

Microscopy	Finding	Significance
Light microscopy (LM)	Hypercellularity, mesangial widening, diffuse mesangial proliferation and formation of crescent ^[6]	Crescents indicate severe disease (RPGN). The proportion of crescentic glomeruli correlates with prognosis
Electron microscopy (EM)	Electron-dense deposits in mesangium ^[6]	Confirms immune complex deposition in the mesangial region
Immunofluorescence (IF)	Deposition of IgA in the mesangium with staghorn pattern ^[6]	This is the diagnostic finding. "Staghorn" refers to the branching pattern of IgA staining along the mesangial tree. May also show IgG, IgM, C3 co-deposition

Immunofluorescence pattern most helpful for diagnosis ^[13]. The granular pattern of IgA staining in the mesangium is what clinches the renal diagnosis and distinguishes it from ANCA vasculitis (pauci-immune) or anti-GBM disease (linear).

Grade	LM Finding	Clinical Correlate
I	Minimal glomerular abnormalities	Mild haematuria
II	Mesangial proliferation (focal or diffuse)	Haematuria ± proteinuria
III	Focal crescents (< 50% glomeruli) or sclerosis	Moderate nephritis
IV	Diffuse crescents (50–75% glomeruli) or sclerosis	Severe nephritis, risk of RPGN
V	Diffuse crescents ( > 75% glomeruli) or sclerosis	Very severe, high risk of ESRD
VI	Membranoproliferative-like changes	Variable

Think of it as three tiers:

Tier 1 — Essential (all patients):

CBC with differential (confirm normal platelets) ^[4]^[6]
Clotting profile (confirm normal coagulation) ^[4]^[6]
Urinalysis (screen for haematuria/proteinuria) ^[4]^[6]
RFT (baseline renal function) ^[4]^[6]
BP measurement ^[6]

Tier 2 — Organ damage assessment & DDx narrowing:

ESR/CRP ^[4]^[6]
LFT (albumin) ^[4]^[6]
Serum complement C3/C4 ^[4]^[6]
Serum IgGAM ^[4]^[6]
ANA, anti-dsDNA, ANCA (rule out SLE, ANCA vasculitis) ^[4]^[6]
ASOT titre (confirm streptococcal trigger) ^[4]^[6]
USG abdomen (if significant GI symptoms) ^[6]^[8]
USG testes (if scrotal pain) ^[6]

Tier 3 — Reserved for atypical/severe cases:

Skin biopsy (atypical rash, uncertain diagnosis)
Renal biopsy (AKI, nephrotic-range proteinuria, persistent proteinuria > 1 month, nephritic syndrome at presentation)
Anti-GBM, cryocrit, blood cultures (specific clinical indications)
CXR/CT thorax (if pulmonary symptoms — rare in IgAV)

This is critical because renal involvement can develop weeks to months after the initial presentation [4a].

Timeframe	Monitoring	Rationale
Acute phase	Urinalysis + BP at each visit	Detect evolving renal involvement early
After resolution	Serial BP + urinalysis Q1–2 weeks for several months [4a]	Renal disease can appear late
Long-term	FU with BP & urine dipstick for 2 years (risk of developing GN) ^[8]	CKD can develop up to 6 months (rarely longer) after diagnosis; 1–2% develop CKD [4a]
If proteinuria present	Quantify with UPCR or 24-hour urine protein; serial RFT	Persistent proteinuria > 1g/day or nephrotic-range → renal biopsy

Don't Discharge and Forget!

The biggest pitfall in IgAV management is assuming the disease is "benign" and not following up the renal status. Rarely CKD (1–2%) can occur up to 6 months after diagnosis [4a]. Every child with IgAV needs at least 6 months to 2 years of serial urinalysis and BP monitoring, even if the initial presentation was mild [4a]^[8].

High Yield Summary — Diagnosis

Diagnosis of HSP is largely clinical. NO laboratory findings are diagnostic of HSP ^[6]
EULAR/PRINTO/PRES 2010: Mandatory purpura + ≥1 of: abdominal pain, IgA on biopsy, arthritis/arthralgia, renal involvement (sensitivity 100%, specificity 87%)
Two essential "rule-out" tests: (1) Normal platelets → not ITP/DIC/TTP, (2) Normal coagulation → not coagulopathy ^[4]^[6]
C3 is NORMAL in HSP — this distinguishes it from PSGN (↓C3), SLE (↓C3/C4), and cryoglobulinaemia (↓C4) ^[6]^[16]^[14]
Serum IgA is elevated in 50–70% — supportive but not diagnostic ^[6]
Skin biopsy (if needed): leukocytoclastic vasculitis with IgA deposition = pathognomonic [4a]^[6]
Renal biopsy indications: AKI, nephritic syndrome at presentation, nephrotic-range proteinuria, or persistent proteinuria > 1 month ^[6]
Renal biopsy findings identical to IgA nephropathy: LM — mesangial proliferation ± crescents; EM — mesangial EDD; IF — IgA staghorn pattern ^[2]^[5]^[6]
Immune complex GN with normal C3 + granular IF with IgA = IgAV/IgAN ^[16]^[14]
Long-term FU: BP + urine dipstick for 2 years ^[8]

Active Recall - Diagnosis of IgA Vasculitis

References

^[2] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (pp. 997, 1764 — IgAN/HSP identical renal pathology, CHCC definition) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 460 ^[4], p. 461 [4a] — HSP diagnostic evaluation, skin/renal biopsy, management, follow-up) ^[5] Senior notes: Ryan Ho Urogenital.pdf (pp. 58–59 — IgA nephropathy pathology and relationship with HSP) ^[6] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (pp. 698, 701, 702, 703 — HSP diagnosis, biochemical tests, biopsy, radiology) ^[7] Senior notes: Maksim Medicine Notes.pdf (p. 233 — FA GASP mnemonic, HSP summary) ^[8] Senior notes: Maksim Surgery Notes.pdf (p. 336 — HSP investigations and FU with BP and urine dipstick for 2 years) ^[13] Senior notes: Ryan Ho Fundamentals.pdf (p. 360 — nephritic syndrome evaluation, complement levels, IF pattern, serology) ^[14] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 413, 421 — GN classification by IF pattern and complement) ^[16] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 1006 — immune complex disease classified by complement level)

Management of IgA Vasculitis (Henoch-Schönlein Purpura)

The overarching philosophy is simple:

Management: supportive treatment as mainstay (usually recover spontaneously) [4a]

IgAV is self-limiting in the vast majority of children, with the disease resolving within approximately 4 weeks [4a]. Treatment is therefore stratified by severity and organ involvement, escalating from supportive care through corticosteroids to immunosuppressants only when specific indications arise.

The key management questions are:

Is this child/adult acutely unwell, or just uncomfortable?
Is there GI involvement severe enough to require steroids?
Is there renal involvement, and if so, how severe?
Are there surgical complications (intussusception, perforation)?

Vasculitis management: steroid ± other immunosuppressants ^[17] — this is the general principle for all vasculitides, but IgAV is unique in being the mildest and most self-limiting.

3. Treatment Modalities — Detailed

Intervention	Detail	Rationale
Adequate hydration and rest [4a]	Oral fluids, bed rest during acute phase	Self-limiting disease; rest reduces hydrostatic pressure in dependent vessels (may reduce purpura severity); hydration maintains renal perfusion
Elevation of legs	Encourage leg elevation during acute purpuric episodes	Reduces hydrostatic pressure in LL vessels → may reduce immune complex deposition and oedema in dependent areas
Education and reassurance	Explain self-limiting nature to parents; warn about possible relapse	Majority are self-limiting lasting around 4 weeks [4a]; 1/3 develop recurrence within 4–6 months (but milder symptoms) [4a]

3.2 Analgesia

Aspect	Detail
Indication	Paracetamol for abdominal pain ^[8]; joint pain; mild-moderate pain
Dose	15 mg/kg/dose PO q4–6h (max 60 mg/kg/day or 4 g/day in adults)
MoA	Central COX inhibition → ↓prostaglandin synthesis in CNS → ↓pain perception + antipyresis. Does NOT have significant peripheral anti-inflammatory effects and does NOT affect platelet function
Why first line?	Safe; no GI mucosal irritation; no renal effects; no platelet dysfunction. Given that HSP already causes GI and renal vasculitis, avoiding drugs that worsen these is logical
Contraindications	Severe hepatic impairment; known hypersensitivity

Aspect	Detail
Indication	Self-limiting, analgesia with NSAIDs ^[7] — for moderate joint pain not adequately controlled by paracetamol
Examples	Ibuprofen 10 mg/kg/dose PO q6–8h; naproxen
MoA	"NSAID" = Non-Steroidal Anti-Inflammatory Drug. Inhibits COX-1/COX-2 → ↓prostaglandins → ↓inflammation, pain, and fever. The peripheral anti-inflammatory effect makes them more effective than paracetamol for arthritis
Why second line?	Because NSAIDs carry specific risks in IgAV
Contraindications/Cautions	Avoid if ongoing GI bleeding or develop GN [4a]

Why Avoid NSAIDs in GI Bleeding and GN?

Two important reasons:

GI bleeding: NSAIDs inhibit COX-1 in gastric mucosa → ↓protective prostaglandin (PGE₂) → ↓mucus/bicarbonate secretion → mucosal erosion. In a patient whose GI mucosa is already damaged by vasculitis and submucosal haemorrhage, adding an NSAID dramatically increases bleeding risk.
GN: NSAIDs inhibit prostaglandin-mediated afferent arteriolar vasodilation → ↓renal blood flow → ↓GFR. In a patient with HSP nephritis (already compromised GFR from glomerular inflammation), NSAIDs can precipitate or worsen AKI.

Bottom line: NSAIDs are fine for skin + joint-only disease, but must be avoided once GI or renal involvement is present [4a].

3.3 Corticosteroids

This is the most commonly tested area in exams. Understand the indications, limitations, and what steroids do NOT do.

Aspect	Detail
Indications	(1) Severe pain despite analgesia [4a]; (2) GI bleed / intussusception: steroids ^[7]; (3) Steroid for reducing risk of persistent renal disease and severe abdominal pain ^[8]; (4) Severe subcutaneous oedema (e.g., scrotal, periorbital); (5) Orchitis
Dose	Prednisolone 1–2 mg/kg/day (max 60–80 mg/day) for 1–2 weeks, then taper over 1–2 weeks
MoA	Glucocorticoids suppress the immune-inflammatory cascade at multiple levels: ↓NF-κB activation → ↓pro-inflammatory cytokine production (IL-1, IL-6, TNF-α); ↓neutrophil chemotaxis and degranulation; ↓vascular permeability → ↓oedema; ↓immune complex-mediated tissue damage
Why it helps in GI disease	Reduces submucosal oedema and inflammation → ↓abdominal pain, ↓GI bleeding, may reduce intussusception risk by decreasing the "lead point" (submucosal haematoma/oedema)

Corticosteroid if severe pain despite analgesia (does NOT alter clinical course/prognosis) [4a]

This is a crucial teaching point:

Steroids provide symptomatic relief (reduce pain, oedema, GI complications)
They do NOT shorten the overall disease duration
They do NOT prevent relapses
Their role in preventing nephritis remains controversial — some data suggest early steroid use may reduce the incidence of persistent renal disease, but the evidence is not conclusive enough to recommend routine prophylactic steroids for all HSP patients

Aspect	Detail
Indication	Severe HSP nephritis with crescentic GN on biopsy (RPGN); nephrotic syndrome; rapidly deteriorating renal function
Dose	IV methylprednisolone 10–30 mg/kg/day (max 1 g/day) for 3 consecutive days ("pulse"), followed by oral prednisolone 1–2 mg/kg/day taper
Why IV pulse?	Delivers a massive, rapid anti-inflammatory effect to halt the rapidly progressive glomerular destruction. The goal is to "rescue" glomeruli before irreversible fibrosis/sclerosis develops
MoA	Same as oral prednisolone but at supraphysiological doses; additionally induces lymphocyte apoptosis and profound immunosuppression

Steroids, cytotoxic agents and plasmapheresis if progress into RPGN ^[2]^[5] — this applies to both IgAN and IgAV nephritis given their identical renal pathology.

Side Effect	Mechanism	Relevance to IgAV
Hyperglycaemia	↑gluconeogenesis, ↑insulin resistance	Monitor blood glucose, especially if on high-dose pulse
Immunosuppression	↓WBC function → ↑infection risk	Especially important in children (already triggered by infection)
GI irritation	↓prostaglandin-mediated mucosal protection	Already have GI vasculitis → consider PPI cover
Osteoporosis	↓osteoblast activity, ↑osteoclast activity	Less relevant for short courses (1–2 weeks)
Growth retardation	↓GH/IGF-1 axis	Concern if prolonged courses needed in children
Adrenal suppression	HPA axis suppression with prolonged use	Taper gradually if used > 2 weeks
HTN, fluid retention	Mineralocorticoid effect	Monitor BP (already monitoring for GN)

3.4 Immunosuppressants (Chronic/Severe Renal Disease)

Immunosuppressant if chronic HSP [4a]

Specifically, immunosuppressants are used for:

Crescentic GN / RPGN on renal biopsy
Persistent proteinuria > 1 g/day despite ACEI/ARB and steroids
Steroid-dependent or steroid-resistant nephritis
Chronic/relapsing course not responding to supportive care and steroids

Drug	Indication in IgAV	MoA	Key Side Effects
Cyclophosphamide ("cyclo" = circle, "phosphamide" = phosphoramide mustard alkylating agent)	Crescentic GN ^[7]; severe nephritis	Alkylates DNA → cross-links DNA strands → prevents cell division → kills rapidly dividing lymphocytes and suppresses immune response	Haemorrhagic cystitis (always give with MESNA + hydration); bone marrow suppression; ↑infection risk; gonadal toxicity (infertility); ↑malignancy risk (bladder ca)
Azathioprine (AZA)	Maintenance therapy after induction; steroid-sparing	Purine analogue → inhibits DNA/RNA synthesis → suppresses lymphocyte proliferation	Bone marrow suppression; hepatotoxicity; GI upset; check TPMT before starting (TPMT deficiency → severe myelosuppression)
Mycophenolate mofetil (MMF)	Alternative to AZA; used in some paediatric centres	Inhibits inosine monophosphate dehydrogenase (IMPDH) → selectively inhibits purine synthesis in lymphocytes (lymphocytes are uniquely dependent on de novo purine pathway)	GI upset (diarrhoea, nausea); bone marrow suppression; teratogenic (contraindicated in pregnancy)
Rituximab (RTX)	Refractory disease; "ritux-" from its chimeric nature, "-mab" = monoclonal antibody	Anti-CD20 monoclonal antibody → depletes B cells → ↓IgA-producing B cells and ↓pathogenic immune complex formation	Infusion reactions; hypogammaglobulinaemia; ↑infection risk (especially PML from JC virus reactivation — rare)

Immunosuppressants only if: (1) Proteinuria > 1g/day despite ACEI, (2) Crescentic GN ^[7]

Regimen: steroids ± cyclophosphamide/azathioprine ^[7]

Phase	Regimen	Duration
Induction	IV pulse methylprednisolone × 3 days → oral prednisolone + cyclophosphamide (or rituximab)	3–6 months
Maintenance	Oral prednisolone (taper) + azathioprine (or MMF)	12–18 months, then reassess

RPGN management: usually require IV pulse steroids ± other immunosuppressants (e.g. cyclophosphamide, rituximab). Plasma exchange for fulminant disease ^[7]

Aspect	Detail
Indication	Tight BP control and proteinuria: ACEI/ARB ^[7]; any IgAV patient with proteinuria > 0.5 g/day or hypertension
Examples	Enalapril, ramipril (ACEI); losartan, valsartan (ARB)
MoA	Block angiotensin II → dilate efferent arteriole → ↓intraglomerular pressure → ↓proteinuria → slows progression to CKD. Also has direct anti-fibrotic and anti-inflammatory effects on glomerulus
Goal	Keep proteinuria < 1 g/day or UPCR < 0.5–1 g/g [13a]
Contraindications	Bilateral renal artery stenosis; pregnancy; hyperkalaemia; AKI with oliguria
Monitoring	Cr and K⁺ 1–2 weeks after initiation (expect small ↑Cr, acceptable if < 30% rise); ongoing BP and proteinuria monitoring
Additional measures	Low salt and protein diet ^[2]^[5]

Why ACEI/ARB in Proteinuric Renal Disease?

The efferent arteriole is constricted by angiotensin II. Blocking angiotensin II causes efferent arteriolar dilation → reduces the pressure driving filtration across the damaged glomerulus → less protein is forced across → less proteinuria. Importantly, persistent proteinuria itself causes tubulointerstitial fibrosis (protein in the tubular lumen is toxic to tubular cells), so reducing proteinuria with ACEI/ARB directly slows CKD progression. This is a universal principle that applies to all proteinuric nephropathies including IgAV/IgAN [13a].

3.6 Management of Specific Complications

Aspect	Detail
Recognition	Severe colicky abdominal pain, bilious vomiting, red-currant jelly stools, sausage-shaped mass
Diagnosis	USG abdomen: look for intussusception ^[8] — target/doughnut sign
Type in HSP	Usually ileo-ileal (small bowel), not ileocolic
Management	Ileo-ileal: less likely to respond to pneumatic/hydrostatic reduction → often requires surgical reduction (or may resolve spontaneously). Ileocolic (if present): USG-guided air or hydrostatic enema reduction. Concurrent steroids may help reduce the "lead point" (submucosal oedema)
Surgical indications	Failed non-operative reduction; peritonitis; perforation; ischaemic bowel

Aspect	Detail
Initial management	IV fluid resuscitation; cross-match blood; correct coagulopathy (if any); IV PPI
Specific therapy	GI bleed / intussusception: steroids ^[7] — IV methylprednisolone to reduce vasculitic inflammation
Endoscopy	May be needed for diagnosis and localisation of bleeding; rarely therapeutic intervention needed
Surgery	Reserved for uncontrollable haemorrhage or perforation

Aspect	Detail
First line	ACEI/ARB (dual benefit: BP control + renal protection)
Second line	Calcium channel blockers (amlodipine); diuretics (if fluid overload)
Target	< 90th percentile for age/sex/height in children; < 130/80 mmHg in adults

If IgAV nephritis presents with nephrotic-range proteinuria:

Anti-proteinuric therapy with ACEI/ARB [13a]
Anti-oedema therapy: salt restriction + loop diuretics [13a]
Corticosteroids ± immunosuppressants (based on renal biopsy findings)
Consider thromboprophylaxis if severe nephrotic syndrome with very low albumin (high VTE risk)

Common Mistake	Why It's Wrong
Starting steroids routinely for all HSP patients	Steroids do NOT alter clinical course/prognosis [4a] — only indicated for specific complications
Using NSAIDs with active GI bleeding	Avoid if ongoing GI bleeding [4a] — worsens mucosal damage
Using NSAIDs with GN	Avoid if develop GN [4a] — ↓renal perfusion via prostaglandin inhibition
Prophylactic antibiotics	HSP is immune-mediated, not infective. No role for prophylactic antibiotics (unlike rheumatic fever post-strep)
Discharging without follow-up plan	Rarely CKD (1–2%) can occur up to 6 months after diagnosis [4a] — need serial BP and urinalysis monitoring

Timepoint	Action	Rationale
During acute illness	BP + urinalysis at each visit	Detect evolving renal involvement
After resolution	Serial BP, urinalysis Q1–2 weeks for several months after dx [4a]	Renal disease can develop late
Long-term	FU with BP & urine dipstick for 2 years (risk of developing GN) ^[8]	Long-term renal monitoring is the most important aspect of follow-up
If significant renal involvement	Monitor RFT, UPCR, BP Q1–3 months; consider paediatric nephrology referral	Progressive proteinuria or ↓GFR requires escalation

Aspect	Detail
Overall	Majority have excellent outcome [4a]
Duration	Majority are self-limiting lasting around 4 weeks [4a]
Relapse	1/3 develop recurrence within 4–6 months (but milder symptoms) [4a]
CKD risk	Rarely CKD (1–2%) can occur up to 6 months after diagnosis [4a]; adults have higher risk of ESRD
Prognostic factors for poor renal outcome	Age > 10 years at onset; adult-onset disease; nephrotic-range proteinuria; crescentic GN on biopsy; persistent proteinuria > 1 g/day; hypertension; ↑Cr at presentation
IgAN comparison	In IgAN (renal-limited), 30% develop ESRD over 30 years ^[5] — IgAV with persistent nephritis follows a similar trajectory

Severity	Clinical Features	Management
Mild	Skin ± joints only	Supportive care + paracetamol ± NSAIDs (if no GI/renal involvement)
Moderate	GI pain, mild GI bleeding	Paracetamol → if inadequate: oral prednisolone 1–2 mg/kg/day × 1–2 weeks + taper
Severe GI	Intussusception, severe haemorrhage, perforation	IV steroids + surgical consultation; USG-guided reduction for ileocolic intussusception; surgery if failed/complicated
Mild renal	Isolated haematuria ± mild proteinuria	ACEI/ARB + serial monitoring (BP + urinalysis)
Moderate renal	Persistent proteinuria > 1 month, nephrotic-range	Renal biopsy → oral prednisolone + ACEI/ARB
Severe renal	RPGN, crescentic GN, AKI	IV pulse methylprednisolone × 3 days → oral pred + cyclophosphamide (or rituximab) ± plasma exchange
Chronic/relapsing	Steroid-dependent or steroid-resistant	Immunosuppressants: AZA, MMF, or rituximab
ALL patients	Regardless of severity	FU with BP & urine dipstick for 2 years ^[8]

High Yield Summary — Management

Supportive treatment is the mainstay — most cases recover spontaneously within 4 weeks [4a]
Analgesia: Paracetamol first line ^[8]; NSAIDs for joint pain but AVOID if GI bleeding or GN [4a]^[7]
Corticosteroids for severe pain despite analgesia, GI bleeding, or intussusception [4a]^[7]^[8]; steroids do NOT alter clinical course/prognosis [4a] — they provide symptomatic relief only
Immunosuppressants (cyclophosphamide/AZA/rituximab) only for crescentic GN or proteinuria > 1 g/day despite ACEI ^[7]
ACEI/ARB for all patients with proteinuria or hypertension — reduces intraglomerular pressure and slows CKD progression ^[7][13a]
Intussusception in HSP: diagnosed by USG; usually ileo-ileal (may need surgical reduction); GI bleed/intussusception: steroids ^[7]
ALL patients need long-term follow-up: BP + urine dipstick for 2 years ^[8] because CKD (1–2%) can occur up to 6 months after diagnosis [4a]
Majority have excellent outcome; 1/3 relapse within 4–6 months but milder symptoms [4a]

Active Recall - Management of IgA Vasculitis

References

^[2] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 997 — IgAN treatment: steroids, cytotoxic agents, plasmapheresis for RPGN) [4a] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 461 — management, prognosis, follow-up of HSP) ^[5] Senior notes: Ryan Ho Urogenital.pdf (pp. 58–59 — IgAN management approach, risk factors for progression) ^[7] Senior notes: Maksim Medicine Notes.pdf (p. 233 — HSP management: self-limiting, NSAIDs, steroids for GI bleed/intussusception; IgAN immunosuppressant indications and regimen; RPGN management) ^[8] Senior notes: Maksim Surgery Notes.pdf (p. 336 — HSP: paracetamol, steroid for severe pain/renal disease, FU BP and urine dipstick for 2 years) [13a] Senior notes: Ryan Ho Fundamentals.pdf (p. 368 — general approach to glomerulonephropathy management: ACEI/ARB, anti-oedema, lipid-lowering, anti-thrombotic) ^[17] Senior notes: Maksim Medicine Notes.pdf (p. 332 — vasculitis overview: steroid ± immunosuppressants)

Complications of IgA Vasculitis (Henoch-Schönlein Purpura)

Although IgAV is largely a self-limiting disease with an excellent overall prognosis in children, complications can occur and some are life-threatening. The complications mirror the organs affected by the IgA-mediated small vessel vasculitis: skin, GI tract, kidneys, scrotum, and CNS. The most important determinant of long-term morbidity is renal involvement.

Think of complications in two time frames:

Acute complications (during the active disease, first 4–6 weeks)
Chronic/delayed complications (weeks to months after initial presentation)

1. Gastrointestinal Complications

GI complications are the most frequent acute complications. They arise because IgA immune complex deposition in submucosal vessels causes haemorrhage, oedema, and ischaemia of the bowel wall.

MOST common gastrointestinal complication of HSP [6c]

Aspect	Detail
Frequency	Occurs in approximately 2–5% of children with IgAV
Pathophysiology	Oedema and haemorrhage act as a pathological lead point contributing to the development of intussusception [6c]. The swollen, haemorrhagic bowel wall segment is "caught" by peristalsis and telescopes into the adjacent distal bowel
Type	Usually ileo-ileal (small bowel intussusception) — because submucosal haemorrhage can occur anywhere along the small bowel, not just at the ileocaecal junction. This contrasts with idiopathic intussusception in infants which is typically ileocolic
Presentation	Severe colicky abdominal pain (worse than baseline HSP pain), bilious vomiting, red-currant jelly stools [6b], palpable sausage-shaped mass
Diagnosis	USG abdomen: look for intussusception ^[8] — target/doughnut sign on transverse view, pseudokidney sign on longitudinal
Management	Ileo-ileal intussusception is less likely to respond to air/hydrostatic enema reduction → may require surgical reduction or resolve spontaneously. Concurrent corticosteroids help reduce the submucosal oedema acting as the lead point. GI bleed / intussusception → steroids ^[7]
Complication of intussusception	Bowel ischaemia → necrosis → perforation → peritonitis (if reduction delayed)

Why Ileo-Ileal, Not Ileocolic?

In idiopathic intussusception (infants 6–36 months), the lead point is typically hypertrophied Peyer's patches concentrated at the terminal ileum → the ileum telescopes into the caecum (ileocolic). In HSP, the lead point is submucosal haemorrhage/oedema from vasculitis, which can occur at any small bowel segment → ileum telescopes into ileum (ileo-ileal). This distinction matters because ileo-ileal intussusception is harder to reduce non-operatively ^[8].

Aspect	Detail
Frequency	Occult blood in ~50% of patients; overt GI bleeding in ~5–10%
Pathophysiology	GI bleeding due to gastrointestinal petechiae [6b] — vasculitis of submucosal vessels → mucosal erosion → bleeding into the GI lumen
Presentation	Melaena (upper GI source), haematochezia (lower GI), occult blood on stool testing, iron deficiency anaemia from chronic occult loss
Severity	Usually self-limiting. Massive haemorrhage requiring transfusion is rare but can occur
Management	IV fluid resuscitation, blood transfusion if needed, corticosteroids to reduce vasculitic inflammation, PPI for upper GI sources. Endoscopy for localisation if severe. Surgery rarely needed

Aspect	Detail
Frequency	Rare (< 1%) but life-threatening
Pathophysiology	Transmural bowel wall necrosis from severe vasculitis → full-thickness ischaemic injury → perforation → faecal peritonitis
Presentation	Sudden worsening of abdominal pain, peritonism (guarding, rigidity, rebound tenderness), fever, tachycardia, shock
Diagnosis	Erect CXR or CT abdomen showing free intraperitoneal air (pneumoperitoneum)
Management	Surgical emergency — urgent laparotomy with resection of perforated segment and peritoneal lavage. Concurrent IV steroids and broad-spectrum antibiotics

Steroid Caution in Abdominal HSP

Steroid may obscure the signs and symptoms of abdominal catastrophes [6c]. This is a critical clinical teaching point: corticosteroids suppress pain, fever, and inflammatory signs. A child on steroids for HSP abdominal pain who develops perforation may NOT show the expected peritonism — the steroids mask the signs. Always have a low threshold for imaging (USG/CT) if a child on steroids has persistent or worsening abdominal symptoms.

Aspect	Detail
Pathophysiology	Severe bowel wall oedema and inflammation → impaired myenteric plexus function → loss of coordinated peristalsis → functional obstruction without mechanical cause
Presentation	Nausea and vomiting — intestinal obstruction due to intussusception or paralytic ileus [6b]; abdominal distension, absent bowel sounds
Diagnosis	AXR: dilated bowel with fluid levels consistent with decreased intestinal motility [6b]; USG to exclude mechanical obstruction
Management	Conservative: NPO, NG decompression, IV fluids. Usually resolves as vasculitis settles

Aspect	Detail
Pathophysiology	Severe vasculitis with thrombosis of submucosal arterioles → segmental bowel ischaemia → if prolonged, transmural necrosis
Presentation	Severe constant (not colicky) abdominal pain, bloody diarrhoea, signs of sepsis, lactic acidosis
Management	Surgical resection of necrotic bowel; IV antibiotics; ICU support
Frequency	Rare

2. Renal Complications

Renal disease is the single most important determinant of long-term morbidity in IgAV. While the acute disease is self-limiting, the nephritis can persist or progress long after the other features have resolved.

Renal disease can occur up to 6 months after diagnosis [6c]
Recommended for children to undergo serial monitoring of BP and urinalysis for several months after diagnosis to monitor development of GN [6c]
FU with BP and urinalysis Q1–2 weeks for the first 1–2 months [6c]
FU with BP & urine dipstick for 2 years (risk of developing GN) ^[8]

Severity	Clinical Features	Frequency	Prognosis
Isolated microscopic haematuria	Dipstick blood positive, no proteinuria, normal RFT	Most common (~35%)	Excellent — usually resolves completely
Haematuria + proteinuria	Combined microscopic haematuria and sub-nephrotic proteinuria	~20–25%	Good if proteinuria resolves within months
Nephritic syndrome	Haematuria, proteinuria, HTN, ↑Cr, oedema	~5–10%	Requires close monitoring; may need biopsy
Nephrotic syndrome	Heavy proteinuria ( > 3.5 g/day in adults, > 40 mg/m²/hr in children), hypoalbuminaemia, oedema, hyperlipidaemia	~5%	Significant risk of CKD; needs biopsy + treatment
RPGN / Crescentic GN	Rapidly rising Cr, haematuria, proteinuria, oligo-anuria	~2–5%	Haematuria, proteinuria and rapidly decreasing RFT that leads to ESRD within 2 weeks of onset if untreated ^[7] — medical emergency

Aspect	Detail
Overall CKD risk	Chronic renal disease develops in 1–2% of children with HSP [4a][6c]
ESRD risk	ESRD develops in up to 8% of children with HSP nephritis [6c] — i.e., among those who develop nephritis, 8% progress to ESRD
Adults	Adults are at increased risk of developing significant renal involvement including ESRD ^[6] — adult IgAV has more aggressive renal disease
Pathophysiology	Ongoing IgA immune complex deposition → persistent mesangial inflammation → progressive glomerulosclerosis and tubulointerstitial fibrosis → irreversible nephron loss → CKD → ESRD
IgAN comparison	Since IgAV and IgAN have identical renal pathology ^[2]^[5], the renal prognosis parallels IgAN: 30% of IgAN patients develop ESRD over 30 years ^[2]^[5]

Risk Factor	Why It Matters
Age > 10 years or adult onset	Older patients have more aggressive renal involvement
Nephrotic-range proteinuria	Persistent heavy proteinuria itself damages tubular cells → tubulointerstitial fibrosis → accelerated CKD
Crescentic GN on biopsy	Crescents indicate severe glomerular injury; > 50% crescents = high risk of ESRD
Persistent proteinuria > 1 month	Failure to resolve suggests ongoing active disease
↑Cr at presentation	↓GFR/↑Cr or presence of AKI: 7-year ESRD rate 2.5% if Cr < 111, 26% if 111–147, 71% if > 148 ^[5]
Concomitant HTN	Accelerates glomerular damage through increased intraglomerular pressure
Histological severity	Based on Oxford classification (MEST criteria): mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, tubular atrophy ^[7]

If HSP nephritis produces nephrotic-range proteinuria, the patient faces the standard complications of nephrotic syndrome:

Complication	Pathophysiology
Oedema	Hypoalbuminaemia → ↓intravascular oncotic pressure → fluid shifts to interstitium
Venous thromboembolism	Loss of antithrombin III (AT-III) in urine + ↑hepatic synthesis of clotting factors + ↑platelet aggregation + hypovolaemia → hypercoagulable state
Infection	Loss of immunoglobulins (especially IgG) in urine → functional hypogammaglobulinaemia; pneumococcal infection is classically important (spontaneous bacterial peritonitis in nephrotic children)
Hyperlipidaemia	↑hepatic lipoprotein synthesis (compensatory response to low albumin) → ↑LDL, ↑VLDL → accelerated atherosclerosis long-term
AKI	Severe hypovolaemia (underfilling) → pre-renal AKI superimposed on glomerular disease

Rapidly progressive glomerulonephritis: a clinical syndrome, NOT a specific aetiological form of GN [13b]

RPGN can complicate IgAV when there is massive immune complex deposition overwhelming the mesangium → extensive crescent formation ( > 50% of glomeruli):

Pathogenesis of crescent formation: a non-specific response to severe injury to glomerular capillary wall → massive movement of plasma product into Bowman's space → subsequent massive influx of macrophages/T cells → formation of cellular crescent [13b]
Followed by fibroblast proliferation and replacement by fibrous crescent (unlikely to respond to immunosuppressive treatment) [13b] — this is why early aggressive treatment is critical: once cellular crescents become fibrous, the damage is irreversible
IgAV-related RPGN falls under Type II RPGN (granular IF, immune complex-mediated) ^[7][13b]

Complication	Detail
Scrotal oedema and pain	Occurs in ~15% of boys; vasculitis of cremasteric and scrotal vessels → oedema mimicking testicular torsion
Why it's a "complication"	Presentation may mimic testicular torsion but evaluation with USG demonstrate normal or increased flow in HSP when compared to decreased flow to testes in torsion [6b]. The danger is unnecessary surgical exploration if torsion is not excluded by imaging, OR delayed surgery for actual torsion if misattributed to HSP
Orchitis	True inflammatory involvement of the testis (rare); usually self-limiting with supportive care ± steroids
Management	Doppler USG to exclude torsion → if flow is normal/increased → conservative management (analgesia, scrotal elevation, ice). If flow absent → surgical exploration for torsion

CNS involvement: caused by hypertension or CNS vasculitis. Presents with intracerebral haemorrhage, seizures, headache and behavioural changes [6b]

Complication	Pathophysiology	Frequency
Headache	Hypertensive encephalopathy (from HSP nephritis → HTN) or direct CNS vasculitis → perivascular inflammation	Uncommon but under-recognised
Seizures	Hypertensive encephalopathy → cerebral oedema → cortical irritation; or direct vasculitis → focal ischaemia	Rare (< 2%)
Intracerebral haemorrhage (ICH) ^[4]	CNS vasculitis → vessel wall necrosis → rupture → parenchymal haemorrhage. Also can occur secondary to severe hypertension	Very rare but devastating
Behavioural changes	Subtle ischaemic injury to frontal/temporal lobes from CNS vasculitis; or side effect of corticosteroid therapy (steroid psychosis)	Rare
Posterior reversible encephalopathy syndrome (PRES)	Severe acute hypertension from HSP nephritis → breakdown of cerebral autoregulation → vasogenic oedema predominantly in posterior circulation (parieto-occipital)	Rare; presents with headache, visual disturbance, seizures, altered consciousness

Two Pathways to CNS Complications

CNS complications in IgAV can arise via two distinct mechanisms:

Direct CNS vasculitis — IgA deposition in cerebral small vessels (rare, unpredictable)
Secondary to hypertension from HSP nephritis — this is more common and potentially preventable through BP monitoring and treatment

This is why serial BP monitoring is so critical — it's not just about tracking renal function, it's also about preventing hypertensive neurological emergencies [6c]^[8].

Aspect	Detail
Frequency	1/3 develop recurrence within 4–6 months (but milder symptoms) [4a]
Pattern	Relapses are usually shorter and less severe than the initial episode; typically skin ± joint involvement. Renal involvement in relapses is less common but can occur
Trigger	Often triggered by a new URTI
Management	Same approach as initial episode: supportive care, analgesia, steroids if needed. Re-screen renal involvement with urinalysis and RFT
Prognosis	Relapse frequency decreases over time; most children have no further episodes after the first year

Complication	Pathophysiology	Detail
Protein-losing enteropathy	Vasculitis of GI mucosal vessels → increased mucosal permeability → albumin and protein loss into the GI lumen	Contributes to hypoalbuminaemia due to renal or intestinal protein loss ^[4]; may coexist with nephrotic-range proteinuria making hypoalbuminaemia more severe
Pancreatitis	Vasculitis of pancreatic small vessels → parenchymal ischaemia and inflammation	Presents with epigastric pain radiating to back, ↑amylase/lipase; rare but reported
Hydrops of gallbladder	Vasculitis of gallbladder wall vessels → oedema → non-calculous gallbladder distension	Presents with RUQ pain; USG shows distended gallbladder without stones; usually self-limiting
Pulmonary haemorrhage	Vasculitis of pulmonary capillaries (rare in IgAV; more common in ANCA vasculitis)	Haemoptysis, infiltrates on CXR; if present, consider alternative diagnosis (MPA, GPA, Goodpasture)
Myocarditis	IgA deposition in cardiac small vessels → myocardial inflammation	Extremely rare; ECG changes, ↑troponin, ↓LV function
Ureteral/ureteric involvement	Vasculitis-related ureteral oedema → obstructive uropathy	Extremely rare; hydroureteronephrosis on imaging

System	Complication	Frequency	Key Points
GI	Intussusception	~2–5%	Most common GI complication; ileo-ileal; USG diagnosis; may need surgical reduction [6c]
	GI haemorrhage	~5–10% overt	Usually self-limiting; steroids for severe
	Bowel perforation	< 1%	Surgical emergency; steroids may mask signs [6c]
	Paralytic ileus	Uncommon	Conservative management
	Bowel ischaemia/necrosis	Rare	Surgical resection if full-thickness
Renal	CKD	1–2% of all HSP	Can develop up to 6 months after diagnosis [4a][6c]
	ESRD	Up to 8% of those with HSP nephritis	More common in adults [6c]
	RPGN / Crescentic GN	2–5%	Medical emergency; Type II RPGN; needs pulse steroids + CYC ^[7]
	Nephrotic syndrome complications	Variable	VTE, infection, hyperlipidaemia
Scrotal	Oedema mimicking torsion	~15% boys	Doppler USG to distinguish; flow normal/increased in HSP
CNS	ICH, seizures, headache, behavioural changes	< 2%	Caused by HTN or CNS vasculitis [6b]
	PRES	Very rare	Secondary to hypertension
Other	Recurrence	~33%	Milder; within 4–6 months [4a]
	Protein-losing enteropathy	Uncommon	Contributes to hypoalbuminaemia
	Pancreatitis	Rare	Vasculitis of pancreatic vessels

Prognostic Factor	Detail
Overall prognosis	Excellent [6c]
Children	~90% recover fully without sequelae
Adults	At increased risk of developing significant renal involvement including ESRD ^[6]
Duration	Majority self-limiting lasting around 4 weeks [4a]
Relapse	1/3 within 4–6 months; milder [4a]
Renal long-term	CKD 1–2% overall; ESRD up to 8% of those with nephritis [6c]
Mortality	Extremely low in children; rare deaths from bowel perforation, massive GI haemorrhage, or severe RPGN

High Yield Summary — Complications

GI complications: Intussusception is the most common GI complication [6c]; usually ileo-ileal; diagnosed by USG. Other GI complications: haemorrhage, perforation (surgical emergency), paralytic ileus, bowel necrosis
Steroids may obscure signs of abdominal catastrophes [6c] — maintain high index of suspicion for perforation/intussusception in a child on steroids with worsening abdominal pain
Renal complications are the most important determinant of long-term morbidity: CKD develops in 1–2% of children; ESRD in up to 8% of those with HSP nephritis [6c]. Renal disease can occur up to 6 months after diagnosis [6c] — hence the need for FU with BP & urine dipstick for 2 years ^[8]
RPGN is a medical emergency; falls under Type II RPGN (granular IF, IC-mediated); cellular crescents must be treated aggressively before they become fibrous (irreversible) [13b]
CNS complications: caused by hypertension or CNS vasculitis — ICH, seizures, headache, behavioural changes [6b]
Scrotal involvement mimics testicular torsion — always perform Doppler USG (preserved flow in HSP vs absent flow in torsion)
Recurrence in ~1/3 within 4–6 months but milder symptoms [4a]
Adults have worse renal prognosis than children ^[6]

Active Recall - Complications of IgA Vasculitis

References

^[2] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 997 — IgAN/HSP identical renal pathology; IgAN prognosis: 30% ESRD over 30 years) ^[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 460 — neurological complications: ICH, seizure, headache, behavioural changes) [4a] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 461 — prognosis: self-limiting 4 weeks, 1/3 recurrence, CKD 1-2% up to 6 months) ^[5] Senior notes: Ryan Ho Urogenital.pdf (pp. 58–59 — IgAN prognosis, risk factors for ESRD, identical pathology to HSP) ^[6] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 698 — adults at increased risk of ESRD) [6b] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 701 — GI involvement, scrotal involvement, CNS involvement) [6c] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 704 — complications: intussusception most common GI complication, bowel perforation, paralytic ileus, GI haemorrhage, bowel ischaemia; renal complications: CKD 1-2%, ESRD up to 8% of HSP nephritis; steroid caution) ^[7] Senior notes: Maksim Medicine Notes.pdf (p. 233 — GI bleed/intussusception: steroids; RPGN classification and management; MEST criteria) ^[8] Senior notes: Maksim Surgery Notes.pdf (p. 336 — FU with BP and urine dipstick for 2 years; USG for intussusception) [13b] Senior notes: Ryan Ho Fundamentals.pdf (p. 361 — RPGN pathogenesis: crescent formation, cellular to fibrous, classification by IF)

High Yield Summary

Definition: IgAV (HSP) is an immune complex-mediated small vessel vasculitis with IgA1-dominant deposits affecting capillaries, venules, and arterioles ^[1]^[2]^[3]
Epidemiology: Most common systemic vasculitis in childhood; peak age 6–7 years; M > F; more common in winter/spring, often after URTI ^[1]^[4]^[6]
Pathogenesis: Mucosal infection → aberrant galactose-deficient IgA1 production → immune complex formation → deposition in small vessel walls → leukocytoclastic vasculitis with IgA-containing immune complexes → complement activation + neutrophil recruitment → vessel wall damage → end-organ injury ^[4]^[6]
Clinical tetrad: (1) Palpable purpura (must be present), (2) Arthralgia/arthritis, (3) Abdominal pain, (4) Renal disease ^[1]^[4]^[6]^[7]
Classical triad from GC lecture: Acute onset / rapid resolution — Palpable purpura, Arthritis, Abdominal pain ^[1]
Key pathology point: IgAV and IgA nephropathy have IDENTICAL renal histopathology (mesangial IgA deposition); IgAV is the systemic form, IgAN is renal-limited ^[2]^[4]^[5]
Palpable purpura is palpable because of inflammatory infiltrate (not just RBC extravasation) — distinguishes from thrombocytopenic purpura which is flat
Intussusception in HSP is usually ileo-ileal (not ileocolic) and the submucosal haemorrhage acts as a pathological lead point ^[8]
Normal platelets and coagulation — purpura occurs despite normal haemostatic parameters ^[6]
Adults have worse renal prognosis than children

High Yield Summary — Differential Diagnosis

Palpable purpura = vasculitis or bacteraemia ^[10]. IgAV purpura is raised, papular, and sometimes tender — this distinguishes it from flat thrombocytopenic purpura ^[12]
IgAV has NORMAL platelets and NORMAL coagulation — this is a defining criterion ^[4]^[6]
IgAV has NORMAL complement (C3/C4) despite being immune-complex mediated — key differentiator from PSGN (↓C3), lupus (↓C3/C4), and cryoglobulinaemia (↓C4) ^[5]^[13]^[14]
IgA nephropathy has identical renal histopathology to IgAV — the difference is the presence of extra-renal manifestations (purpura, arthralgia, abdominal pain) ^[2]^[5]
URTI timing: concurrent → IgAV/IgAN; 7–10 days after → PSGN ^[5]^[13]
Meningococcaemia is a life-threatening condition that cannot be missed [6a] — a febrile child with rapidly progressive purpura needs urgent blood cultures and empiric antibiotics before any other workup
The three "must-not-miss" diagnoses when a child presents with purpura: (1) Meningococcaemia, (2) Leukaemia (pancytopenia), (3) NAI/child abuse (trauma pattern)

High Yield Summary — Diagnosis

Diagnosis of HSP is largely clinical. NO laboratory findings are diagnostic of HSP ^[6]
EULAR/PRINTO/PRES 2010: Mandatory purpura + ≥1 of: abdominal pain, IgA on biopsy, arthritis/arthralgia, renal involvement (sensitivity 100%, specificity 87%)
Two essential "rule-out" tests: (1) Normal platelets → not ITP/DIC/TTP, (2) Normal coagulation → not coagulopathy ^[4]^[6]
C3 is NORMAL in HSP — this distinguishes it from PSGN (↓C3), SLE (↓C3/C4), and cryoglobulinaemia (↓C4) ^[6]^[16]^[14]
Serum IgA is elevated in 50–70% — supportive but not diagnostic ^[6]
Skin biopsy (if needed): leukocytoclastic vasculitis with IgA deposition = pathognomonic [4a]^[6]
Renal biopsy indications: AKI, nephritic syndrome at presentation, nephrotic-range proteinuria, or persistent proteinuria > 1 month ^[6]
Renal biopsy findings identical to IgA nephropathy: LM — mesangial proliferation ± crescents; EM — mesangial EDD; IF — IgA staghorn pattern ^[2]^[5]^[6]
Immune complex GN with normal C3 + granular IF with IgA = IgAV/IgAN ^[16]^[14]
Long-term FU: BP + urine dipstick for 2 years ^[8]

High Yield Summary — Management

Supportive treatment is the mainstay — most cases recover spontaneously within 4 weeks [4a]
Analgesia: Paracetamol first line ^[8]; NSAIDs for joint pain but AVOID if GI bleeding or GN [4a]^[7]
Corticosteroids for severe pain despite analgesia, GI bleeding, or intussusception [4a]^[7]^[8]; steroids do NOT alter clinical course/prognosis [4a] — they provide symptomatic relief only
Immunosuppressants (cyclophosphamide/AZA/rituximab) only for crescentic GN or proteinuria > 1 g/day despite ACEI ^[7]
ACEI/ARB for all patients with proteinuria or hypertension — reduces intraglomerular pressure and slows CKD progression ^[7][13a]
Intussusception in HSP: diagnosed by USG; usually ileo-ileal (may need surgical reduction); GI bleed/intussusception: steroids ^[7]
ALL patients need long-term follow-up: BP + urine dipstick for 2 years ^[8] because CKD (1–2%) can occur up to 6 months after diagnosis [4a]
Majority have excellent outcome; 1/3 relapse within 4–6 months but milder symptoms [4a]

High Yield Summary — Complications

GI complications: Intussusception is the most common GI complication [6c]; usually ileo-ileal; diagnosed by USG. Other GI complications: haemorrhage, perforation (surgical emergency), paralytic ileus, bowel necrosis
Steroids may obscure signs of abdominal catastrophes [6c] — maintain high index of suspicion for perforation/intussusception in a child on steroids with worsening abdominal pain
Renal complications are the most important determinant of long-term morbidity: CKD develops in 1–2% of children; ESRD in up to 8% of those with HSP nephritis [6c]. Renal disease can occur up to 6 months after diagnosis [6c] — hence the need for FU with BP & urine dipstick for 2 years ^[8]
RPGN is a medical emergency; falls under Type II RPGN (granular IF, IC-mediated); cellular crescents must be treated aggressively before they become fibrous (irreversible) [13b]
CNS complications: caused by hypertension or CNS vasculitis — ICH, seizures, headache, behavioural changes [6b]
Scrotal involvement mimics testicular torsion — always perform Doppler USG (preserved flow in HSP vs absent flow in torsion)
Recurrence in ~1/3 within 4–6 months but milder symptoms [4a]
Adults have worse renal prognosis than children ^[6]

IgA Vasculitis (Henoch-Schoenlein Purpura)

1. Definition

2. Epidemiology

2.1 Incidence and Burden

2.2 Demographics

2.3 Relationship with Infections

3. Anatomy and Function of Affected Structures

3.1 Small Vessels (the target)

3.2 The IgA System

3.3 The Mesangium

4. Aetiology (Focus on Hong Kong Context)

5. Pathophysiology

5.1 Step-by-Step Pathogenesis

Step 1: Trigger → Aberrant IgA1 Response

Step 2: Immune Complex Formation

Step 3: Deposition in Small Vessels

Step 4: Inflammatory Cascade

Step 5: End-Organ Damage

5.2 Relationship with IgA Nephropathy

6. Classification

6.1 Chapel Hill Consensus Conference (CHCC 2012) Classification

6.2 EULAR/PRINTO/PRES Classification Criteria (2010)

6.3 ACR 1990 Criteria (Historical, for adults)

6.4 Classification by Organ Involvement Severity

7. Clinical Features

7.1 General Presentation

7.2 Symptoms (with Pathophysiological Basis)

A. Skin Symptoms (~100% eventually, ~75% at presentation)

B. Musculoskeletal Symptoms (~75%)

C. Gastrointestinal Symptoms (~80%)

D. Urogenital Symptoms (~50%)

E. Neurological Symptoms (rare, < 5%)

F. Constitutional Symptoms

7.3 Signs (with Pathophysiological Basis)

A. Skin Signs

B. Musculoskeletal Signs

C. Abdominal Signs

D. Renal Signs

E. Scrotal Signs

7.4 Timing and Evolution of Symptoms

7.5 Differences Between Paediatric and Adult Presentation

8. Summary Table: Clinical Features by Organ System

Active Recall - IgA Vasculitis (HSP)

References

1. Differential Diagnosis Framework: By Presenting Feature

2. Differential Diagnosis of Purpura (Comprehensive)

2.1 Vasculitis (Palpable Purpura)

2.2 Thrombocytopenic Causes (Non-Palpable Purpura)

2.3 Coagulopathies (Non-Palpable Purpura/Ecchymoses)

2.4 Vessel Wall Fragility (Non-Palpable Purpura)

3. Differential Diagnosis by Organ-System Overlap

3.1 DDx of GN Component (Nephritic Syndrome)

3.2 DDx of Abdominal Pain Component

3.3 DDx of Scrotal Pain/Swelling Component

3.4 DDx of Fever + Rash in Children

4. Key Differentiating Investigations at a Glance

5. Summary: How to Differentiate IgAV from Key Mimics

Active Recall - DDx of IgA Vasculitis

1. Diagnostic Principles

2. Classification / Diagnostic Criteria

2.1 EULAR/PRINTO/PRES 2010 Classification Criteria (Paediatric — Most Widely Used)

2.2 ACR 1990 Criteria (Adults — Historical)

2.3 CHCC 2012 Definition (Nomenclature, not diagnostic criteria)

3. Diagnostic Algorithm

3.1 Clinical Approach — Step-by-Step

3.2 When is the Diagnosis Straightforward?

3.3 When is the Diagnosis Challenging?

4. Investigation Modalities — Systematic

4.1 Bedside Assessment

4.2 Blood Tests

A. To Exclude Dangerous Mimics

B. To Assess Organ Damage

C. To Narrow the Differential (Serology)

D. Interpretation of Complement Levels in Nephritic Syndrome — Key Discriminator

4.3 Urinalysis (The Most Important Monitoring Investigation)

4.4 Imaging

4.5 Histology (Biopsy)

A. Skin Biopsy

B. Renal Biopsy

ISHN (International Study of Kidney Disease in Children) Classification of HSP Nephritis