Waldenström macroglobulinaemia is a lymphoplasmacytic lymphoma characterized by clonal proliferation of B lymphocytes in the bone marrow with overproduction of monoclonal immunoglobulin M (IgM), leading to hyperviscosity and cytopenias.

Waldenström Macroglobulinaemia (WM)

Waldenström Macroglobulinaemia (WM) — let's break the name down:

"Waldenström" — named after Jan Gösta Waldenström, the Swedish physician who first described the condition in 1944.
"Macro-" (Greek: makros = large) + "globulin" (Latin: globulus = small sphere, referring to globular serum proteins) — meaning a large globulin protein.
"-aemia" (Greek: haima = blood) — meaning "in the blood."

So the name literally means: a condition where large globulin proteins (IgM) are present in excess in the blood, as originally described by Waldenström.

Waldenström macroglobulinaemia (WM) is defined as bone marrow lymphoplasmacytic lymphoma (LPL) that is associated with an IgM M protein (monoclonal protein) of any size ^[1]^[2].

To unpack this further, WM sits at the intersection of two concepts:

Lymphoplasmacytic lymphoma (LPL): A type of B-cell lymphoma arising from post-germinal centre (post-GC) B cells that have undergone somatic hypermutation but have NOT yet undergone immunoglobulin class switching ^[1]. This is crucial — because the malignant clone is "stuck" at the IgM stage of B-cell differentiation (before class switch to IgG, IgA, etc.), the paraprotein it secretes is always IgM.
Monoclonal IgM (IgM M protein): The clonal B cells produce a single species of immunoglobulin — specifically IgM. IgM is the largest immunoglobulin (a pentamer, ~970 kDa), which is why it causes hyperviscosity far more readily than IgG or IgA.

Key Terminology Distinctions (High Yield)

The terminology around monoclonal IgM is important and frequently tested ^[1]:

Macroglobulinaemia: ANY excess monoclonal IgM production — this is a laboratory finding, not a diagnosis by itself.
- Includes: WM, Smouldering WM (SWM), IgM MGUS, CLL/lymphoma-related monoclonal IgM, AL amyloidosis.
Waldenström macroglobulinaemia (WM): BM LPL + IgM M protein (of any size).
Smouldering WM (SWM): Asymptomatic WM — a premalignant state with risk of progression to symptomatic WM.
Lymphoplasmacytic lymphoma (LPL): The underlying B-cell lymphoma — can occur in BM and elsewhere.
IgM MGUS can progress into both SWM/WM (if associated with LPL in BM) and IgM MM (uncommon, if associated with plasma cell infiltration in BM) ^[1].

WM is a rare disease ^[1].

Parameter	Detail
Incidence	~3 per million per year in the US ^[1]; accounts for ~1–2% of haematological malignancies
Median age at diagnosis	~70 years ^[1] — this is a disease of the elderly
Sex	60% male (M > F) ^[1]
Ethnicity	Much more common in Caucasians than in other ethnic groups ^[1]; relatively rare in Asian and African populations
Familial predisposition	~20% of WM patients have a first-degree relative with WM or another B-cell lymphoproliferative disorder — suggesting genetic susceptibility

Hong Kong / Asian Context

WM is uncommon in Hong Kong and East Asia compared to Western populations. In HK, other lymphoproliferative disorders (e.g., DLBCL, T/NK-cell lymphomas) are more prevalent ^[3].
However, clinicians must still recognise WM because of increasing life expectancy and the ageing population in Hong Kong.
When a Chinese patient presents with monoclonal IgM, the differential diagnosis must include other causes of macroglobulinaemia (e.g., marginal zone lymphoma, CLL with IgM secretion) more prominently, given the relative rarity of WM in this population.

3. Anatomy and Function: The Normal B-Cell Maturation Pathway

Understanding WM requires understanding where in B-cell development things go wrong.

4. Aetiology and Risk Factors

4.1 Genetic Factors

The vast majority of WM cases are associated with MYD88 mutation ^[1].

Similar to how multiple myeloma develops from MGUS → smouldering myeloma → myeloma ^[4], WM exists on a spectrum:

Stage	Definition	Risk of Progression
IgM MGUS	Serum IgM M protein < 30 g/L, BM lymphoplasmacytic infiltration < 10%, no symptoms/end-organ damage	~1.5% per year to WM or related disorder
Smouldering WM (SWM)	Meets criteria for WM (IgM M protein + BM LPL) but asymptomatic — no end-organ damage	~12% per year in first 5 years, then lower (~2% per year)
Symptomatic WM	BM LPL + IgM M protein + symptoms/end-organ damage attributable to disease	Requires treatment

High Yield: Spectrum of Monoclonal IgM Disorders

IgM MGUS can progress into both SWM/WM (if associated with LPL in BM) and IgM multiple myeloma (uncommon, if associated with plasma cell infiltration in BM) ^[1]. This mirrors the MGUS → smouldering myeloma → myeloma progression for IgG/IgA paraproteins ^[4]. The key difference is that WM arises from LPL (B-cell lymphoma), while IgM MM arises from plasma cells — they are distinct diseases despite both producing IgM.

5. Pathophysiology

The clinical features of WM arise from two distinct mechanisms ^[1]:

The IgM M protein itself causes disease through several mechanisms ^[1]:

Mechanism	Pathophysiology	Clinical Consequence
Hyperviscosity	IgM is a pentamer (~970 kDa) → even moderate levels cause marked increase in serum viscosity → sluggish blood flow, especially in microcirculation	Hyperviscosity syndrome: blurred vision, headache, epistaxis, mucosal bleeding, confusion, stroke
Autoantibody activity (IgM against self-antigens)	Monoclonal IgM may bind: (a) myelin-associated glycoprotein (MAG) → demyelination; (b) RBC antigens (usually "I" antigen) → cold agglutinin disease	Neuropathy (anti-MAG); Cold autoimmune haemolytic anaemia (cold AIHA) ^[1]
Cryoglobulinaemia	IgM precipitates at temperatures below 37°C (in peripheral/cold-exposed areas) → immune complex deposition → vasculitis	Raynaud phenomenon, purpura, skin ulceration, glomerulonephritis, neuropathy
Organ deposition	IgM or light chains deposit in tissues	Renal disease, GI tract involvement, skin infiltration ^[1]; AL amyloidosis (if light chain deposition)
Coagulopathy	IgM interferes with clotting factor function, coats platelets → impaired platelet aggregation and fibrin clot formation	Mucosal bleeding, bruising
Immunoparesis	Suppression of normal immunoglobulin production (polyclonal IgG, IgA) by the malignant clone	Increased susceptibility to infections

Direct infiltration by LPL malignant cells causes ^[1]:

Site of Infiltration	Pathophysiology	Clinical Consequence
Bone marrow	Malignant LPL cells replace normal haematopoietic tissue	Cytopenias — anaemia (most common), thrombocytopaenia, neutropaenia
Lymph nodes	Malignant LPL cells infiltrate lymph nodes	Lymphadenopathy (usually modest; not as bulky as aggressive NHL)
Liver and spleen	Malignant LPL cells infiltrate hepatic sinusoids and splenic red pulp	Hepatosplenomegaly
Extramedullary sites	Rarely: lung, GI tract, skin, CNS (Bing-Neel syndrome)	Organ-specific symptoms

Bing-Neel Syndrome: A rare but important complication where malignant LPL cells infiltrate the CNS (leptomeninges and/or brain parenchyma), causing headache, confusion, cranial nerve palsies, and ataxia. Named after the physicians who first described CNS involvement in WM.

6. Classification

WM is one of several monoclonal gammopathies — conditions defined by the production of a monoclonal immunoglobulin (paraprotein / M protein):

Condition	Cell of Origin	Paraprotein	Key Features
MGUS	Plasma cell or lymphoplasmacytic cell	Any Ig (IgG > IgM > IgA)	Asymptomatic, < 30 g/L M protein, < 10% BM cells, no end-organ damage
Multiple Myeloma	Plasma cell	Usually IgG or IgA (rarely IgM)	CRAB criteria (Ca↑, Renal, Anaemia, Bone lesions) ^[4]
Waldenström Macroglobulinaemia	Lymphoplasmacytic cell (LPL)	IgM	Hyperviscosity, neuropathy, cold AIHA
AL Amyloidosis	Plasma cell or LPL	Light chains (λ > κ)	Organ deposition of amyloid fibrils
Light Chain Deposition Disease	Plasma cell	Light chains	Non-amyloid light chain deposition

WM vs. Multiple Myeloma — Key Distinctions (High Yield)

Feature	WM	Multiple Myeloma
Cell of origin	Post-GC B cell / LPL	Terminally differentiated plasma cell
Paraprotein	IgM	Usually IgG or IgA
Bone lesions	Rare (no lytic lesions)	Common (lytic lesions, pathological fractures)
Hyperviscosity	Common (~10–30%)	Rare (~2%, usually IgA or IgG3)
Neuropathy	Common (anti-MAG)	Uncommon (unless amyloidosis)
Lymphadenopathy	Present (~15–20%)	Rare
Hepatosplenomegaly	Present	Rare
MYD88 L265P	>90%	Very rare (<5%)
Bone marrow	Lymphoplasmacytic infiltrate	Sheets of plasma cells
Osteolytic lesions	Absent	Present — key distinguishing feature

7. Clinical Features

7.1 Symptoms

Constitutional symptoms, e.g., fatigue, weakness, weight loss, B symptoms ^[1]:

Symptom	Pathophysiological Basis
Fatigue / weakness	Anaemia (BM infiltration → reduced erythropoiesis); cytokine-mediated (IL-6, TNF)
Weight loss	Chronic catabolic state due to malignancy; cytokine-driven (TNF-α = "cachectin")
Night sweats / fever (B symptoms)	Cytokine release from malignant cells (IL-6, IL-1, TNF); less prominent than in aggressive NHL
Anorexia	Cytokine-mediated appetite suppression

This is the hallmark clinical syndrome of WM and is much more common here than in any other paraproteinaemia. Why? Because IgM is a pentamer — it increases viscosity far more per gram than IgG or IgA.

Normal serum viscosity: 1.4–1.8 centipoise (cp) relative to water. Symptoms typically begin at: 4–5 cp (roughly corresponding to IgM levels > 30–40 g/L, though this varies between patients).

Symptom	Pathophysiological Basis
Blurred vision / visual disturbance	Hyperviscous blood causes sluggish flow through retinal vessels → retinal vein engorgement, haemorrhages, papilloedema. The retina is exquisitely sensitive to perfusion changes.
Headache	Increased intracranial venous pressure due to sludging of hyperviscous blood in cerebral venous sinuses
Dizziness / vertigo	Impaired microcirculation in the inner ear / brainstem
Confusion / altered mental status	Cerebral hypoperfusion; sludging in CNS microvasculature
Epistaxis / oronasal bleeding / mucosal bleeding	Distended mucosal vessels rupture under increased intravascular pressure; IgM also interferes with platelet function and coagulation factors
Stroke-like symptoms	Sludging → thrombosis in cerebral vessels
Heart failure (high-output)	Increased plasma volume and viscosity → increased cardiac workload

IgM against self-antigens → neuropathy (myelin Ag) ^[1].

Symptom	Pathophysiological Basis
Distal, symmetric, sensorimotor polyneuropathy	Monoclonal IgM binds myelin-associated glycoprotein (MAG) on Schwann cells → demyelination of peripheral nerves. Typically affects sensory > motor fibres, starting distally (length-dependent).
Numbness, tingling, paraesthesiae in feet/hands	MAG antibodies target myelin in longest nerves first (feet → hands)
Gait unsteadiness / ataxia	Loss of proprioception due to large-fibre sensory neuropathy
Weakness (late)	Progressive demyelination eventually affects motor fibres

Anti-MAG neuropathy has a characteristic pattern on nerve conduction studies: demyelinating neuropathy with disproportionately prolonged distal motor latencies (because MAG is concentrated at the paranodal regions of distal nerve segments).

IgM precipitation in cold temperature → cryoglobulinaemia ^[1]:

Symptom	Pathophysiological Basis
Raynaud phenomenon	Monoclonal IgM (acting as a cryoglobulin) precipitates in cooled peripheral blood vessels → vasospasm and vascular occlusion → digital ischaemia
Cold urticaria	Immune complex deposition in skin triggered by cold exposure
Acrocyanosis	Persistent cyanosis of extremities due to cryoglobulin-mediated microvascular obstruction
Livedo reticularis	Mottled, net-like purplish discolouration of skin due to sluggish flow in dermal venules

Cold AIHA (RBC Ag) ^[1]:

Symptom	Pathophysiological Basis
Episodes of dark urine (haemoglobinuria) after cold exposure	Monoclonal IgM acts as a cold agglutinin (binds RBC "I" antigen at < 37°C) → complement activation → intravascular haemolysis
Jaundice	Haemolysis → unconjugated hyperbilirubinaemia
Fatigue / pallor (anaemia)	Chronic haemolysis
Acrocyanosis / digital ischaemia	Agglutination of RBCs in peripheral (cool) circulation → microvascular occlusion

Symptom	Pathophysiological Basis
Mucosal bleeding (epistaxis, gingival bleeding)	IgM coats platelets → impaired platelet adhesion and aggregation; IgM interacts with clotting factors (especially vWF and fibrinogen); hyperviscosity distends mucosal vessels
Bruising	Platelet dysfunction + coagulopathy
GI bleeding (rare)	Amyloid deposition in GI vessels (if AL amyloidosis complicates WM)

Symptom	Pathophysiological Basis
Recurrent sinopulmonary infections	Immunoparesis — suppression of normal polyclonal IgG and IgA production by the expanding malignant clone → functional hypogammaglobulinaemia ^[6]
Opportunistic infections (less common)	Neutropaenia from BM infiltration; treatment-related immunosuppression

Symptom	Pathophysiological Basis
Symptoms of anaemia (fatigue, dyspnoea on exertion, palpitations)	BM infiltration by LPL cells → reduced normal erythropoiesis; also contributed by haemolysis (cold AIHA), haemodilution (increased plasma volume), and cytokine-mediated suppression
Easy bruising / bleeding	Thrombocytopaenia from BM infiltration
Recurrent infections	Neutropaenia from BM infiltration + immunoparesis
Abdominal fullness / early satiety	Hepatosplenomegaly from LPL infiltration
Painless lymph node swelling	Lymphadenopathy from LPL infiltration

Symptom	Pathophysiological Basis
Diarrhoea / malabsorption	GI tract infiltration by LPL cells or amyloid deposition
Skin nodules / papules	Cutaneous infiltration by LPL cells or IgM deposition (Schnitzler syndrome if with chronic urticaria)
Headache, confusion, cranial nerve palsies, ataxia	Bing-Neel syndrome — CNS infiltration by malignant LPL cells
Nephrotic-range proteinuria / renal impairment	Renal deposition of IgM, light chains, or amyloid; cast nephropathy (rare in WM cf. myeloma)

7.2 Signs

Sign	Pathophysiological Basis
Pallor	Anaemia (multifactorial: BM infiltration, haemolysis, haemodilution)
Jaundice (mild)	Haemolysis (cold AIHA → unconjugated hyperbilirubinaemia)
Purpura / ecchymoses	Thrombocytopaenia + platelet dysfunction (IgM coating) + coagulopathy
Weight loss / cachexia (late)	Advanced disease with high tumour burden

Sign	Pathophysiological Basis
Fundoscopy: "sausage-shaped" retinal veins (venous engorgement), retinal haemorrhages, papilloedema	Pathognomonic of hyperviscosity syndrome. Hyperviscous blood causes sluggish retinal venous drainage → veins become tortuous and engorged ("link sausage" or "boxcar" appearance); increased venous pressure → retinal haemorrhages and disc oedema.
Cervical / generalised lymphadenopathy	LPL infiltration of lymph nodes; usually modest (rubbery, non-tender)

Fundoscopy in Hyperviscosity Syndrome — Don't Forget!

Fundoscopy is a critical bedside examination in any patient with suspected WM / hyperviscosity. The finding of dilated, tortuous retinal veins with flame haemorrhages should prompt urgent plasmapheresis. This is a clinical emergency.

Sign	Pathophysiological Basis
Hepatomegaly	LPL infiltration of hepatic sinusoids ^[1]
Splenomegaly	LPL infiltration of splenic red pulp ^[1]. Splenomegaly in WM is usually mild to moderate (not massive, as in CML or myelofibrosis) ^[7]
Ascites (rare)	Advanced disease; may indicate peritoneal involvement or hypoalbuminaemia

Sign	Pathophysiological Basis
Peripheral neuropathy signs: reduced sensation (glove-and-stocking), reduced ankle reflexes, positive Romberg sign, sensory ataxia	Anti-MAG IgM → demyelination of peripheral nerves; large-fibre sensory predominant
Raynaud phenomenon / acrocyanosis	Cryoglobulinaemia / cold agglutinins → precipitation and RBC agglutination in distal circulation
Skin changes: purpura (non-thrombocytopaenic type from cryoglobulins), urticarial rash (Schnitzler syndrome), papules/nodules (cutaneous infiltration)	Various mechanisms: cryoglobulin-mediated vasculitis, direct infiltration, IgM deposition

Sign	Pathophysiological Basis
Signs of heart failure (rare, late)	High-output failure due to increased plasma volume and viscosity; or amyloid cardiomyopathy if AL amyloidosis develops

Mechanism	Key Clinical Features
Hyperviscosity (IgM pentamer)	Visual disturbance, headache, confusion, mucosal bleeding, "sausage" retinal veins
Autoantibody (anti-MAG, anti-RBC)	Peripheral neuropathy, cold AIHA
Cryoglobulinaemia	Raynaud, purpura, skin ulcers, glomerulonephritis
Tissue deposition (IgM / light chains)	Renal disease, GI involvement, skin infiltration, AL amyloidosis
Coagulopathy	Mucosal bleeding, bruising
Immunoparesis	Recurrent infections
BM infiltration	Anaemia, thrombocytopaenia, neutropaenia
Organ infiltration	Lymphadenopathy, hepatosplenomegaly, CNS (Bing-Neel), skin, GI

Risk Factor	Explanation
Higher IgM M protein level	Greater paraprotein burden suggests more aggressive clone
IgM type (vs. IgG MGUS for myeloma)	IgM MGUS has a higher rate of progression to lymphoma (WM/LPL)
Abnormal serum free light chain ratio	Indicates greater clonal restriction
BM infiltration pattern	Higher % of lymphoplasmacytic cells in BM = closer to WM
MYD88 L265P positivity	Present in >90% of WM; its presence in MGUS suggests higher risk of WM (vs. myeloma)
Low IgG / IgA levels (immunoparesis)	Suggests more significant clonal suppression of normal B cells

High Yield Summary

WM = BM lymphoplasmacytic lymphoma (LPL) + IgM M protein of any size. The malignant cell is a post-GC B cell that has undergone somatic hypermutation but NOT class switching → stuck producing IgM.
MYD88 L265P mutation is found in >90% of WM — constitutive NF-κB activation → cell survival + proliferation. Key molecular marker distinguishing WM from other IgM-producing lymphomas.
IgM is a pentamer (~970 kDa) → causes hyperviscosity syndrome far more readily than IgG/IgA. Hyperviscosity is the hallmark complication of WM.
Two mechanisms of disease: (a) IgM protein effects (hyperviscosity, autoantibody activity [anti-MAG neuropathy, cold AIHA], cryoglobulinaemia, tissue deposition, coagulopathy, immunoparesis); (b) Direct tumour infiltration (BM → cytopenias; LN → lymphadenopathy; liver/spleen → hepatosplenomegaly).
Fundoscopy is critical — "sausage-shaped" retinal veins + haemorrhages = hyperviscosity → urgent plasmapheresis.
WM vs. Myeloma: WM has NO lytic bone lesions, IgM paraprotein, lymphadenopathy/hepatosplenomegaly present, MYD88+. Myeloma has lytic bone lesions, IgG/IgA paraprotein, no lymphadenopathy, MYD88−.
Spectrum: IgM MGUS → Smouldering WM → Symptomatic WM. Only symptomatic WM requires treatment.
Rare in Hong Kong/Asians (much more common in Caucasians); median age 70, M > F (60%).

Active Recall - Waldenström Macroglobulinaemia (Definition, Epidemiology, Aetiology, Pathophysiology, Clinical Features)

Differential Diagnosis of Waldenström Macroglobulinaemia

This is the most important tier — when you detect a monoclonal IgM on SPE/immunofixation, what could it be besides WM?

High Yield — Spectrum of Monoclonal IgM Disorders

Macroglobulinaemia means ANY excess monoclonal IgM production. Includes: WM, SWM, IgM MGUS, CLL/lymphoma-related monoclonal IgM, AL amyloidosis ^[1]. This is directly from the lecture framework — you must be able to list these entities and distinguish them.

Condition	Key Distinguishing Features from WM	Why It Mimics WM
IgM MGUS	IgM M protein < 30 g/L; BM lymphoplasmacytic infiltration < 10%; absence of end-organ damage; no symptoms ^[4]^[8]	Shares the same monoclonal IgM. IgM MGUS can progress into both SWM/WM (if associated with LPL in BM) and IgM MM (uncommon, if associated with plasma cell infiltration in BM) ^[1]. Risk of progression ~1.5% per year.
Smouldering WM (SWM)	Meets criteria for WM (IgM M protein of any size + BM LPL) but is asymptomatic — no end-organ damage ^[1]	Identical histology and paraprotein to WM but no symptoms. Distinction matters because SWM does not require treatment — only monitoring ^[1]. Risk of progression ~12%/year in first 5 years ^[1].
CLL with IgM paraprotein	Typically presents with lymphocytosis on CBC; smear/smudge cells on peripheral blood film ^[9]; CD5+, CD23+ immunophenotype (WM is CD5−, CD23−); MYD88 usually wild-type	Some CLL clones secrete monoclonal IgM. However, the cell morphology is small mature lymphocytes (not lymphoplasmacytic), and CLL has a distinctive immunophenotype. CLL may transform to aggressive large cell lymphoma (Richter transformation), most commonly DLBCL ^[9].
Marginal zone lymphoma (MZL) with IgM	May produce monoclonal IgM; MYD88 usually wild-type (vs. >90% positive in WM); specific subtypes (splenic MZL, extranodal MALT lymphoma, nodal MZL) with characteristic features. Classified as indolent lymphoma alongside LPL/WM ^[2]^[5].	Both are indolent B-cell lymphomas that can produce IgM and cause similar symptoms. Splenic MZL can cause prominent splenomegaly, lymphocytosis with villous lymphocytes, and IgM paraprotein — closely mimicking WM. MYD88 mutation status and immunophenotype are the key distinguishers.
IgM multiple myeloma	Very rare (< 1% of MM); plasma cell morphology on BM biopsy (not lymphoplasmacytic); lytic bone lesions present (absent in WM); t(11;14) common; MYD88 wild-type; CRAB features present ^[4]^[8]	Produces IgM paraprotein, but arises from terminally differentiated plasma cells, not LPL. Lytic bone lesions and CRAB criteria distinguish it from WM.
AL amyloidosis with IgM	Organ deposition of amyloid fibrils (heart, kidneys, nerves, GI); Congo red stain positive with apple-green birefringence under polarised light; can present with nephrotic syndrome, restrictive cardiomyopathy, macroglossia, autonomic neuropathy ^[10]	Can arise from the same LPL clone that causes WM (i.e., WM-associated AL amyloidosis) or independently. The key is that AL amyloidosis adds organ damage from amyloid deposition on top of (or instead of) the direct IgM/LPL effects. Most important DDx of MGUS is AL amyloidosis — especially if the patient has suggestive symptoms ^[4].
Heavy chain disease (μ-HCD)	Extremely rare; secretes free μ heavy chains (without light chains); associated with CLL-like morphology; vacuolated plasma cells on BM	Can cause similar lymphoplasmacytic infiltration and IgM-related symptoms, but the biochemical profile differs (free heavy chains rather than intact IgM).

How to Distinguish These Entities — A Practical Approach

Critical Distinguishing Tool: MYD88 L265P

MYD88 L265P is found in >90% of WM ^[1] but is typically wild-type in:

Marginal zone lymphoma
IgM multiple myeloma
CLL (only ~3%)
AL amyloidosis (unless arising from LPL)

Therefore, MYD88 testing is the single most useful molecular test to distinguish WM from its mimics when you have a monoclonal IgM with an ambiguous BM biopsy.

Tier 2: Differential Diagnosis by Dominant Clinical Syndrome

When WM presents not with an incidental IgM finding but with a clinical syndrome, you must consider the broader differential for that syndrome.

Hyperviscosity syndrome is the hallmark of WM, but it can also occur in:

Condition	Mechanism of Hyperviscosity	Why WM Is More Likely
Multiple myeloma	High IgA (can polymerise) or IgG3 (can self-aggregate); rare in MM compared to WM ^[11]	WM causes hyperviscosity far more commonly because IgM is a pentamer (~970 kDa) vs. IgG monomer (~150 kDa). Only ~2% of MM patients develop hyperviscosity vs. ~10–30% of WM patients.
Polycythaemia vera (PV)	Hyperviscosity symptoms: dizziness, headaches due to increased red cell mass and high haematocrit ^[7]^[12]	PV causes hyperviscosity through cellular (erythrocyte) mechanisms, not paraprotein. CBC shows dramatically elevated Hb/Hct. Diagnosis by BM and JAK2 mutation (95%), low EPO ^[12]. No monoclonal IgM.
Acute leukaemia (hyperleukocytosis)	WBC > 100 × 10⁹/L causes leucostasis — physical sludging of blast cells in microvasculature	Acute presentation with blasts on PBS; very different from the indolent course of WM.
Essential thrombocythaemia	Microvascular symptoms: headache, dizziness, erythromelalgia ^[7]	Platelets elevated, not IgM. Mechanism is microvascular platelet plugging, not protein-mediated viscosity.

~20–25% of WM patients develop neuropathy (anti-MAG). The broader DDx for a patient presenting with peripheral neuropathy + monoclonal gammopathy includes:

Condition	Key Features	How to Distinguish from WM Neuropathy
MGUS-associated neuropathy	IgM MGUS with anti-MAG antibodies → identical neuropathy pattern to WM, but without BM infiltration or other WM features	BM biopsy shows < 10% LPL infiltrate; no other symptoms of WM.
POEMS syndrome (Polyneuropathy, Organomegaly, Endocrinopathy, M protein, Skin changes)	Usually IgG or IgA λ paraprotein (NOT IgM); associated with osteosclerotic myeloma (Castleman disease variant)	IgM is unusual in POEMS. Osteosclerotic (not lytic) bone lesions. Dramatically different treatment (radiation to plasmacytoma).
AL amyloidosis	Light chain deposition → amyloid neuropathy (often painful, autonomic)	Congo red positive tissue biopsy; cardiac involvement common; macroglossia.
Diabetic neuropathy	Length-dependent sensorimotor polyneuropathy in diabetic patients	No paraprotein; HbA1c elevated; typically axonal (not demyelinating) on NCS.
CIDP (Chronic Inflammatory Demyelinating Polyneuropathy)	Demyelinating neuropathy; may be associated with paraprotein in some cases	CSF albuminocytological dissociation; response to IVIG/steroids; not specifically IgM-associated.
Drug-induced neuropathy	Chemotherapy (vincristine, bortezomib, thalidomide), isoniazid, metformin (B12 depletion)	Clear temporal relationship with drug exposure.

When a patient presents with haemolytic anaemia exacerbated by cold, the differential includes:

Condition	Key Features	How to Distinguish from WM-Associated CAD
Primary (idiopathic) cold agglutinin disease	Monoclonal IgM cold agglutinins without identifiable underlying lymphoma; typically anti-I specificity; complement-mediated haemolysis	No BM LPL infiltrate; no other WM features. Some cases may represent early/occult LPL. Primary chronic CAD has been considered more difficult to treat than warm-antibody AIHA — lack of efficacy of corticosteroids ^[13].
Infection-associated cold agglutinins	Transient, polyclonal IgM cold agglutinins during Mycoplasma pneumoniae or EBV infection; anti-I (Mycoplasma) or anti-i (EBV)	Acute, self-limiting; polyclonal (not monoclonal); resolves with infection.
Other lymphoproliferative disorders	CLL, MZL, or other lymphomas may produce monoclonal IgM cold agglutinins	Distinguish by BM morphology, immunophenotype, MYD88 status.

When an elderly patient presents with normocytic normochromic anaemia and you find a paraprotein:

Condition	Key Features	How to Distinguish from WM
Multiple myeloma	CRAB criteria: hypercalcaemia, renal insufficiency, anaemia, bone lytic lesions ^[4]^[11]	Lytic bone lesions on skeletal survey/low-dose CT; plasma cell morphology on BM; MYD88 wild-type; usually IgG/IgA paraprotein. Hyperviscosity syndrome: rare c.f. WM ^[11].
MDS (myelodysplastic syndrome)	Cytopenias with dysplastic changes in BM; may have macrocytosis; cytogenetic abnormalities (e.g., del(5q), −7)	No paraprotein; BM shows dysplastic haematopoiesis.
Aplastic anaemia	Pancytopenia with hypocellular BM	No paraprotein; BM is "empty" (hypocellular), not infiltrated.
Anaemia of chronic disease	Normocytic anaemia with low iron, low TIBC, high ferritin; associated with chronic inflammation/infection/malignancy	No paraprotein; clinical context of underlying chronic disease.
BM infiltration by solid tumour metastases	Leukoerythroblastic blood film (left shift + nucleated RBCs + tear-drop cells)	Clinical history of primary malignancy; BM biopsy shows carcinoma cells, not lymphoplasmacytic cells.

WM (LPL) is classified as an indolent (low-grade) B-cell lymphoma ^[2]^[5]. Other indolent and aggressive B-cell lymphomas can cause overlapping features (lymphadenopathy, hepatosplenomegaly, BM infiltration, constitutional symptoms):

Lymphoma	Key Distinguishing Features from WM
Follicular lymphoma	t(14;18) → dysregulated BCL2 ^[3]; no IgM paraprotein; characteristic follicular growth pattern on biopsy; waxing-and-waning lymphadenopathy
Mantle cell lymphoma	t(11;14) → altered cyclin D1 ^[3]; CD5+ (like CLL); more aggressive course; no significant paraprotein
DLBCL	High-grade NHL with rapid proliferation, prominent systemic B symptoms ^[3]; large cells on biopsy; may arise from transformation of indolent lymphoma (including WM/LPL)
CLL/SLL	CD5+, CD23+; smudge cells on PBS ^[9]; may secrete IgM but morphology/immunophenotype distinct
Hairy cell leukaemia	Pancytopenia with monocytopaenia; "hairy" lymphocytes on PBS; BRAF V600E mutation; splenomegaly often massive
Splenic marginal zone lymphoma	Prominent splenomegaly; villous lymphocytes in peripheral blood; may secrete IgM; MYD88 wild-type

Generalised Lymphadenopathy DDx — Lecture Slide High Yield

Differential diagnosis of generalised lymphadenopathy ^[5]:

Neoplastic: leukaemias, lymphomas/LPD
Infective: viral (EBV, CMV), bacterial, mycobacterial, parasitic, dimorphic fungi
Autoimmune
Drugs

WM is one of the neoplastic causes. When evaluating generalised lymphadenopathy, always consider the full differential. Low-grade lymphoma causes waxing-and-waning lymphadenopathy; high-grade lymphoma causes rapidly growing masses with prominent systemic symptoms ^[3].

DDx	Paraprotein	BM Finding	MYD88 L265P	Bone Lesions	Hyperviscosity	Unique Feature
WM	IgM	LPL infiltrate	>90%	Absent	Common (10–30%)	Anti-MAG neuropathy
IgM MGUS	IgM < 30 g/L	< 10% LPL	~50–80%	Absent	Absent	Asymptomatic; monitor
SWM	IgM (any)	≥10% LPL	>90%	Absent	Absent	Asymptomatic; monitor
CLL	IgM (sometimes)	Small lymphocytes, CD5+/CD23+	~3%	Absent	Rare	Smudge cells; Richter transformation
MZL	IgM (sometimes)	Marginal zone morphology	Rare	Absent	Rare	Splenic MZL → massive splenomegaly
IgM MM	IgM	Sheets of plasma cells	Rare	Lytic lesions	Rare	CRAB criteria; t(11;14) common
AL amyloidosis	Light chains (± IgM)	Variable	Variable	Absent	Absent	Congo red+; organ deposition (heart, kidney, nerve)
PV	None	Hypercellular trilineage	JAK2+ (different pathway)	Absent	Common (cellular)	High Hb/Hct; low EPO
DLBCL	Rare	Large B cells	Rare (unless transformed from WM)	May be present	Rare	Aggressive; rapidly growing masses

Think WM when you have the "WM triad":

An elderly Caucasian male (median age 70, M > F)
Monoclonal IgM on SPE/immunofixation (of any size)
One or more of the characteristic IgM-mediated syndromes (hyperviscosity, anti-MAG neuropathy, cold AIHA, cryoglobulinaemia) AND/OR bone marrow showing lymphoplasmacytic infiltration

Think away from WM when:

Lytic bone lesions are present → think IgM myeloma or other MM
The patient is young with acute symptoms and blasts → think acute leukaemia
Rapidly growing nodal masses with B symptoms → think DLBCL (though may be transformed WM)
Lymphocytosis with smudge cells and CD5+/CD23+ phenotype → think CLL
Massive splenomegaly without significant IgM or neuropathy → think splenic MZL, hairy cell leukaemia, or MPN ^[7]

Exam Pitfall

Do NOT diagnose WM based on the IgM level alone. Macroglobulinaemia = ANY excess monoclonal IgM production ^[1] — it is a laboratory finding, not a diagnosis. You need BM biopsy showing LPL to confirm WM. Similarly, do not confuse IgM MGUS with WM — only symptomatic WM with end-organ damage requires treatment; MGUS and smouldering WM require monitoring only ^[4]^[1].

High Yield Summary — Differential Diagnosis of WM

Monoclonal IgM is not WM by itself. The DDx of monoclonal IgM includes IgM MGUS, smouldering WM, CLL, marginal zone lymphoma, IgM myeloma, AL amyloidosis, and heavy chain disease.
BM biopsy is essential to distinguish WM (LPL morphology) from CLL (small lymphocytes, CD5+/CD23+), MZL (marginal zone morphology), and IgM MM (plasma cell sheets with lytic lesions).
MYD88 L265P is the key molecular distinguisher — positive in >90% of WM, rare in MZL, CLL, IgM MM.
No lytic bone lesions in WM — if present, think IgM myeloma.
Hyperviscosity DDx includes PV (cellular viscosity from high Hct), hyperleukocytosis (blast sludging), and rarely IgA/IgG3 myeloma — but WM is the most common cause of paraprotein-related hyperviscosity.
Neuropathy + IgM = think WM/MGUS with anti-MAG antibodies; distinguish from POEMS (IgG/IgA λ), AL amyloidosis, CIDP, and diabetic neuropathy.
Cold AIHA + monoclonal IgM = WM-associated CAD vs. primary CAD vs. infection-associated (Mycoplasma, EBV).
The spectrum: IgM MGUS → Smouldering WM → Symptomatic WM mirrors the MGUS → SMM → MM spectrum for IgG/IgA paraproteins.

Active Recall - Differential Diagnosis of Waldenström Macroglobulinaemia

References

^[1] Senior notes: Ryan Ho Haemtology.pdf, Section 3.6.4 (Waldenström Macroglobulinaemia) ^[2] Lecture slides: Block A - Generalised Lymphadenopathy_ Differential diagnosis and principle of management.pdf (indolent lymphoma classification: LPL, MZL, WM) ^[3] Senior notes: Adrian Lui Pediatrics Notes.pdf, Section 11.1.2 (Lymphoma — NHL classification, cytogenetic associations) ^[4] Senior notes: Block A - An old man with bone pain and anaemia_ multiple myeloma; monoclonal gammopathy.pdf (MGUS → smouldering → myeloma spectrum; MGUS definition; AL amyloidosis as DDx) ^[5] Senior notes: Block A - Generalised Lymphadenopathy_ Differential diagnosis and principle of management.pdf (DDx of generalised lymphadenopathy) ^[7] Senior notes: Block A - Splenomegaly_ common causes of splenomegaly; myeloproliferative diseases.pdf (PV, ET clinical features and diagnosis) ^[8] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (spectrum of monoclonal gammopathy; IgM MGUS → SWM → WM table) ^[9] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (CLL presentation, smear cells, Richter transformation) ^[10] Senior notes: Block A - Hematology Data Interpretation.pdf (AL amyloidosis, Congo red stain, immunoparesis) ^[11] Senior notes: Maksim Medicine Notes.pdf (MM clinical features; hyperviscosity rare cf. WM) ^[12] Lecture slides: GC 086. Splenomegaly.pdf (PV: diagnosis by JAK2, low EPO; hyperviscosity symptoms; clinical features) ^[13] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (cold AIHA treatment; DAT; CAD difficult to treat)

Diagnostic Criteria, Algorithm and Investigations for Waldenström Macroglobulinaemia

1. Diagnostic Criteria

The diagnosis of WM requires integration of laboratory, histological, immunophenotypic and molecular findings. There is no single blood test that clinches the diagnosis — you need to put together a clinicopathological picture.

All three of the following criteria must be met ^[1]:

Criterion	Detail	Rationale (Why This Criterion?)
1. IgM monoclonal gammopathy of any size in serum	Detected by serum protein electrophoresis (SPE) + immunofixation electrophoresis (IFE). There is no minimum IgM threshold — even a small IgM M protein qualifies.	Unlike multiple myeloma (which requires M protein > 30 g/L or BM plasma cells ≥10% for SMM/MM), WM is defined by the combination of IgM paraprotein + LPL histology + immunophenotype, regardless of IgM size.
2. ≥10% BM infiltration by small lymphocytes exhibiting plasmacytoid or plasma cell differentiation with an intertrabecular pattern	Bone marrow trephine biopsy shows lymphoplasmacytic infiltrate — a mixture of small lymphocytes, plasmacytoid lymphocytes, and plasma cells — growing between the bone trabeculae (intertrabecular pattern, not paratrabecular as in follicular lymphoma).	This is the histological hallmark. The intertrabecular pattern reflects the biology of LPL — it homes to marrow stroma rather than growing along bone surfaces. The mixed morphology (lympho-plasmo-cytic) reflects the differentiation spectrum of the malignant clone: some cells look like lymphocytes, some look like plasma cells, and many are in between ("plasmacytoid").
3. Typical immunophenotype for the infiltrate	See immunophenotype table below	Immunophenotyping by flow cytometry and/or immunohistochemistry (IHC) is essential to confirm LPL and exclude mimics (CLL, MZL, mantle cell lymphoma).

Marker	WM/LPL	CLL/SLL	Mantle Cell Lymphoma	Marginal Zone Lymphoma
CD19	+	+	+	+
CD20	Strongly +	Weakly +	+	+
CD22	+	Weakly +	+	+
CD5	− (occasionally weak +)	+	+	−
CD10	−	−	−	−
CD23	−	+	−	−
CD25	+	Variable	−	Variable
CD103	−	−	−	−
Surface Ig	IgM + (strong)	IgM/IgD (weak)	IgM/IgD	IgM
Cytoplasmic Ig	+ (in plasmacytic component)	−	−	Variable
Cyclin D1	−	−	+ (t(11;14))	−

Key Immunophenotype Pattern for WM — High Yield

The classic WM immunophenotype is: CD19+, CD20+ (strong), CD5−, CD10−, CD23−, surface IgM+ ^[1]. This pattern distinguishes WM from:

CLL (CD5+, CD23+, CD20 weak)
Mantle cell lymphoma (CD5+, cyclin D1+)
Follicular lymphoma (CD10+)

If you see CD5+ or CD23+ in a BM lymphoid infiltrate with IgM paraprotein, you should reconsider the diagnosis — it may be CLL or another lymphoma producing IgM rather than true WM.

This is a critical distinction because only symptomatic WM with end-organ damage requires treatment; MGUS and smouldering WM require monitoring only ^[4]^[1].

Smouldering WM (SWM) is defined as meeting the diagnostic criteria for WM but being asymptomatic — a premalignant state with risk of progression to symptomatic WM ^[1].

Treatment is indicated when the patient has one or more of the following attributable to the disease:

Indication for Treatment	Examples
Symptomatic hyperviscosity	Visual disturbance, headache, mucosal bleeding
Symptomatic cytopenias	Hb < 10 g/dL, platelets < 100 × 10⁹/L
Symptomatic lymphadenopathy / organomegaly	Bulky nodes, symptomatic hepatosplenomegaly
Systemic symptoms	B symptoms (fever, night sweats, weight loss >10%)
Symptomatic peripheral neuropathy	Anti-MAG neuropathy with functional impairment
Symptomatic cryoglobulinaemia	Raynaud, purpura, glomerulonephritis
Cold agglutinin disease	Symptomatic cold AIHA
AL amyloidosis	Organ involvement (cardiac, renal, nerve)

IgM Level Alone Does Not Determine Treatment

A common exam mistake: a high IgM level does NOT automatically mean the patient needs treatment. The IgM M protein can be of any size ^[1] — what matters is whether the patient has symptoms or end-organ damage attributable to the disease. An asymptomatic patient with IgM of 40 g/L but no symptoms is still SWM and should be monitored.

3. Investigation Modalities — Detailed Interpretation

Investigations for WM serve four purposes:

Confirm the paraprotein (SPE, IFE, sFLC)
Confirm the histological diagnosis (BM biopsy)
Assess disease burden and complications (blood tests, imaging, serum viscosity)
Prognostic stratification (IPSSWM scoring)

3.1 Confirming the Paraprotein

SPE is usually performed when there is hypergammaglobulinaemia, suspected plasma cell dyscrasia, suspected AL amyloidosis, unexplained raised ESR, investigation of unexplained neuropathy, heavy proteinuria, or renal impairment ^[14].

How it works: Serum proteins are separated by electrical charge on a gel or capillary. Normal serum shows a large albumin peak and a broad gamma-globulin region (representing polyclonal immunoglobulins from many B-cell clones). A monoclonal protein appears as a sharp, narrow "M spike" (or "M band") in the gamma region — because all molecules are identical (same charge and size), they migrate to the same position.

In WM: A discrete M band is seen in the gamma region. The 4 patterns of SPE ^[14]:

Pattern	Interpretation
Normal Ig pattern, absence of paraprotein	Normal; but could also be non-secretory myeloma ^[14]
Pan-immunoparesis	All Ig low; think inherited or acquired immunodeficiencies, certain forms of myeloma (light chain, IgD, non-secretory) ^[14]
Raised immunoglobulin, absence of paraprotein	Polyclonal hypergammaglobulinaemia — NOT a plasma cell problem; indicates a reactive process. DO NOT refer to haematology ^[14]
Presence of paraprotein ± immunoparesis	Monoclonal gammopathy — requires further workup (IFE, BM biopsy) ^[14]

In WM, you typically see: M spike in gamma region + immunoparesis (suppression of normal IgG and IgA).

Bone marrow aspirate and trephine biopsy is essential and non-negotiable for diagnosing WM ^[1]^[16].

Technique: typically posterior iliac crest; aspirate for smear permits cytology examination, flow cytometry and genetic studies; trephine biopsy permits histological examination (marrow cellularity, architectural details, marrow fibrosis, bone structure) and immunohistochemistry for immunophenotyping ^[16].

Component	What to Look For	Findings in WM
Aspirate (cytology)	Cell morphology	Mixture of small lymphocytes, plasmacytoid lymphocytes, and plasma cells — the "lymphoplasmacytic" spectrum. Mast cells are often increased (a subtle but characteristic finding in LPL/WM).
Trephine (histology)	Growth pattern, cellularity	≥10% intertrabecular infiltrate ^[1]. Unlike follicular lymphoma (paratrabecular) or CLL (diffuse/nodular interstitial). Hypercellular marrow with residual haematopoiesis reduced.
Flow cytometry	Immunophenotype	CD19+, CD20+ (strong), CD5−, CD10−, CD23−, surface IgM+ ^[1]^[17]. Confirms B-cell lineage and excludes CLL (CD5+/CD23+), mantle cell (CD5+/cyclin D1+), follicular (CD10+). Detection of surface immunoglobulin light chains is very helpful in determining clonality of B cell proliferation ^[17].
Immunohistochemistry (IHC)	Additional markers on tissue sections	PAX5+ (B-cell), CD138+ (plasma cell component), cyclin D1− (excludes mantle cell), κ or λ light chain restriction (confirms clonality).
MYD88 L265P	Somatic mutation	>90% positive in WM ^[1]. Tested by AS-PCR or NGS on aspirate DNA. A negative result should prompt reconsideration of the diagnosis.
CXCR4 mutation	Somatic mutation (~30–40%)	Affects treatment response (reduced response to BTK inhibitors) and prognosis. Tested by NGS.
Cytogenetics/FISH	Chromosomal abnormalities	Common findings: del(6q) (~30–50%), trisomy 4. Unlike myeloma, t(4;14), t(14;16), del(17p) are not typical. Unlike follicular lymphoma, t(14;18) is absent. Unlike mantle cell, t(11;14) is absent ^[3].
IgH gene rearrangement by PCR	Determine clonality of B lymphocytes ^[17]	Monoclonal IgH rearrangement confirms B-cell clonality — a single rearrangement pattern is seen because all cells derive from one neoplastic clone ^[17].

Why both aspirate AND trephine? The aspirate gives you individual cell morphology and material for flow cytometry and molecular studies. The trephine gives you the architectural pattern (intertrabecular vs. paratrabecular vs. diffuse) and overall cellularity — both are essential for diagnosis.

3.3 Assessing Disease Burden and Complications

Once the diagnosis is confirmed, the next set of investigations assesses how much disease is present and what damage it has caused.

Finding	Interpretation
Anaemia (most common abnormality)	BM infiltration → reduced erythropoiesis; also contributed by haemolysis (cold AIHA), haemodilution (↑ plasma volume from IgM), and cytokine suppression
Thrombocytopaenia	BM infiltration
Leucopaenia / neutropaenia	BM infiltration
Lymphocytosis (mild)	Occasionally, circulating LPL cells in blood (but frank leukaemic phase is uncommon in WM cf. CLL)

Finding	Interpretation
Rouleaux formation	Stacking of RBCs due to high IgM concentration → altered surface charge → increased ESR. This is not specific to WM (also seen in MM).
RBC agglutination	As seen in cold agglutinin diseases ^[13] — monoclonal IgM cold agglutinin causes RBC clumping at room temperature. The lab may report a spuriously elevated MCV (the analyser counts clumps as single large cells).
Plasmacytoid lymphocytes (rare)	Circulating WM cells — not common, but when present, supports the diagnosis
Polychromasia	If haemolysis is occurring (reticulocytosis)

Test	Expected Finding in WM	Interpretation
Renal function (urea, creatinine, eGFR)	Usually normal or mildly impaired (~3% have renal impairment ^[1])	Renal involvement is uncommon in WM compared to myeloma. When present, think: light chain deposition, amyloidosis, cryoglobulinaemic GN.
Calcium	Usually normal	Hypercalcaemia is rare in WM (unlike myeloma) — because WM does not cause osteolytic lesions and does not activate osteoclasts.
LDH	May be mildly elevated	Reflects tumour burden and haemolysis. LDH — if high indicates high turnover, haemolysis ^[13].
Albumin	May be low	Negative acute phase reactant; also dilutional effect from ↑ plasma volume.
Beta-2 microglobulin (β2M)	Elevated in proportion to tumour burden	Used for prognostic scoring (IPSSWM). Important for prognosis; to be taken at diagnosis as its level will change after treatment ^[18].
Total protein	Often elevated (high globulin fraction)	Reflects the IgM paraprotein contribution to total protein. The albumin-globulin gap widens.
Uric acid	May be elevated	Increased purine turnover from lymphoproliferation.

A particularly important point about calcium in WM: The big IgM molecule can cause interference in the assays ^[19]. Monoclonal IgM can bind calcium, causing factitious hypercalcaemia (falsely elevated calcium on some assays). Paraproteinaemia with ↑IgM can also cause factitious ↑Ca due to direct interference ^[20]. Always correlate with ionised calcium if the total calcium seems discrepant.

IgM Assay Interference — Exam Pearl

Monoclonal IgM is notorious for interfering with multiple laboratory assays. Beyond factitious hypercalcaemia, IgM can interfere with phosphate measurements (Ig may precipitate with PO₄, interfering with measurement ^[20]) and coagulation assays. If lab results seem internally inconsistent in a patient with high IgM, always consider assay interference as an explanation.

Test	Expected Finding	Interpretation
Reticulocyte count	Elevated	Compensatory erythropoiesis in response to haemolysis
LDH	Elevated	Released from lysed RBCs
Unconjugated (indirect) bilirubin	Elevated	Breakdown product of haemoglobin
Haptoglobin	Low or absent	Consumed by binding free haemoglobin released from lysed RBCs
Direct antiglobulin test (DAT / Coombs test)	Positive for C3d (not IgG)	In cold AIHA, IgM binds RBCs in the cold → activates complement → C3d remains on RBC surface after IgM dissociates when blood returns to warm core. DAT positive in immune haemolytic anaemias — C3d in cold AIHA ^[13].
Cold agglutinin titre	Elevated (often > 1:1000)	Confirms the IgM is acting as a cold agglutinin
Thermal amplitude	Determines temperature range of activity	Higher thermal amplitude (closer to 37°C) → more clinically significant haemolysis

Investigation	Finding in WM-Associated Neuropathy
Anti-MAG antibodies	Positive in ~50% of WM patients with neuropathy
Nerve conduction studies (NCS) / EMG	Demyelinating pattern, sensory > motor ^[1]. Characteristically, disproportionately prolonged distal motor latencies — because MAG is concentrated at the paranodal regions of distal nerve terminals
Anti-ganglioside antibodies (anti-GM1, anti-GD1b)	Less common; associated with motor neuropathy or sensory ataxic neuropathy

NCS pattern distinction is high yield: anti-MAG neuropathy in WM = demyelinating, sensory > motor. Compare with: POEMS = motor > sensory; amyloid neuropathy = axonal ^[1].

Modality	Role in WM	Key Findings
CT chest / abdomen / pelvis	Assess for lymphadenopathy and organomegaly	Mild-moderate lymphadenopathy (~25%), hepatomegaly (~24%), splenomegaly (~19%) ^[1]. No lytic bone lesions.
PET-CT	Not routinely required; useful if transformation to DLBCL suspected (high-grade areas light up with high SUV)	WM is indolent and typically shows low-grade FDG uptake. Focally intense uptake may indicate histological transformation.
Skeletal survey / Low-dose whole-body CT	Unlike myeloma, not routinely performed for WM	WM does NOT cause osteolytic lesions — this is a key distinguishing feature from multiple myeloma. If lytic lesions are found, reconsider the diagnosis (IgM myeloma?).
MRI brain / spine	If Bing-Neel syndrome (CNS involvement) suspected	Leptomeningeal enhancement; periventricular white matter lesions; nerve root enhancement

No Lytic Bone Lesions in WM — Key Exam Distinction

Unlike multiple myeloma, which characteristically causes punched out lytic lesions, diffuse osteopenia, pathological fractures ^[18], WM does NOT cause osteolytic bone disease. This is because:

Myeloma activates osteoclasts (via RANKL, MIP-1α, DKK1) → bone destruction
WM/LPL cells do not produce these osteoclast-activating factors

If the question describes lytic bone lesions with IgM paraprotein, think IgM multiple myeloma, not WM.

Investigation	When to Order	What It Shows
Congo red stain (tissue biopsy)	Suspected AL amyloidosis (organ dysfunction: cardiac, renal, neuropathic)	Congo red stain, salmon pink colour → indicative of amyloid deposition; apple-green birefringence under polarised light. Electron microscopy shows non-branching fibrils ^[10].
Tissue biopsy (fat pad, rectal, renal)	Suspected amyloidosis	Amyloid deposits; type confirmed by mass spectrometry or immunohistochemistry (AL vs. AA vs. ATTR)
Echocardiography	Suspected cardiac involvement (amyloidosis, high-output failure)	Restrictive pattern; increased wall thickness with low voltage ECG (if amyloid); high-output features if hyperviscosity-related
CSF analysis	Suspected Bing-Neel syndrome (CNS symptoms)	Flow cytometry on CSF may detect clonal B cells; elevated protein; IgM in CSF

Once WM is diagnosed and treatment is considered, risk stratification guides intensity of therapy.

The IPSSWM uses 5 adverse factors:

Adverse Factor	Threshold
Age	> 65 years
Haemoglobin	≤ 11.5 g/dL
Platelet count	≤ 100 × 10⁹/L
β2-microglobulin	> 3 mg/L
Serum IgM	> 70 g/L

Risk Group	Number of Adverse Factors (excluding age)	With Age ≤ 65	With Age > 65	5-Year Survival
Low	0–1	Any age	—	~87%
Intermediate	2	Any age	OR age > 65 with 0–1 factors	~68%
High	≥ 3	Any age	—	~36%

The revised IPSSWM (rIPSSWM, 2019) has been updated to include serum LDH and albumin as well, but the original IPSSWM is more commonly cited for exam purposes.

Phase	Investigations	Purpose
1. Detect paraprotein	SPE, IFE, quantitative Ig (IgG/A/M), sFLC + ratio, UPE	Identify and characterise IgM M protein; detect immunoparesis
2. Confirm histological diagnosis	BM aspirate + trephine: morphology, flow cytometry, IHC, MYD88, CXCR4, cytogenetics/FISH, IgH rearrangement	Confirm LPL with intertrabecular pattern; typical immunophenotype; MYD88 L265P
3. Assess disease burden	CBC + differential, β2M, LDH, albumin, renal function, calcium, uric acid	Quantify cytopenias; prognostic scoring (IPSSWM)
4. Assess IgM-related complications	Serum viscosity, fundoscopy, haemolysis screen (reticulocytes, LDH, bilirubin, haptoglobin, DAT), cryoglobulins, anti-MAG, NCS/EMG	Identify hyperviscosity, cold AIHA, cryoglobulinaemia, neuropathy
5. Staging / Imaging	CT C/A/P (or PET-CT if transformation suspected)	Assess lymphadenopathy, organomegaly; NO skeletal survey needed (no lytic lesions)
6. Special investigations	Congo red biopsy (if AL amyloidosis suspected); echocardiography; CSF (if Bing-Neel suspected)	Evaluate organ-specific complications

High Yield Summary — Diagnosis of WM

Diagnostic criteria (ALL must be met): (a) IgM monoclonal gammopathy of any size; (b) ≥10% BM lymphoplasmacytic infiltrate in intertrabecular pattern; (c) Typical immunophenotype (CD19+, CD20+ strong, CD5−, CD10−, CD23−).
MYD88 L265P (>90% of WM) is not in the formal criteria but is indispensable for confirming diagnosis and distinguishing WM from mimics (MZL, IgM MM, CLL).
SPE → IFE → BM biopsy is the core diagnostic pathway for any suspected monoclonal gammopathy.
Four SPE patterns: normal, pan-immunoparesis, polyclonal hypergammaglobulinaemia (reactive — do NOT refer to haematology), and paraprotein ± immunoparesis.
Serum viscosity should be measured if IgM > 5 g/dL or symptoms of hyperviscosity. Symptomatic at ≥4 cp.
Fundoscopy is essential — sausage-link retinal veins = hyperviscosity emergency.
No lytic bone lesions in WM — unlike myeloma. If lytic lesions present with IgM, think IgM MM.
Haemolysis screen (LDH, haptoglobin, bilirubin, DAT) if cold AIHA suspected — DAT positive for C3d (not IgG) in cold AIHA.
IPSSWM uses 5 factors: age > 65, Hb ≤ 11.5, Plt ≤ 100, β2M > 3, IgM > 70.
IgM can cause assay interference — factitious hypercalcaemia, phosphate interference, spurious MCV elevation from agglutination.

Active Recall - Diagnostic Criteria, Algorithm and Investigations for WM

References

^[1] Senior notes: Ryan Ho Haemtology.pdf, Section 3.6.4 (Waldenström Macroglobulinaemia — diagnostic criteria, clinical presentation, pathogenesis) ^[2] Lecture slides: Block A - Generalised Lymphadenopathy_ Differential diagnosis and principle of management.pdf (indolent lymphoma classification: LPL and WM) ^[3] Senior notes: Adrian Lui Pediatrics Notes.pdf, Section 11.1.2 (Lymphoma — NHL cytogenetic associations) ^[4] Senior notes: Block A - An old man with bone pain and anaemia_ multiple myeloma; monoclonal gammopathy.pdf (MGUS definition, progression spectrum, work-up for paraprotein, diagnostic criteria for MM) ^[10] Senior notes: Block A - Hematology Data Interpretation.pdf (AL amyloidosis: Congo red stain, electron microscopy, immunoparesis) ^[11] Senior notes: Maksim Medicine Notes.pdf (MM investigations including SPE, UPE, sFLC, immunofixation) ^[13] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (haemolysis workup: LDH, haptoglobin, DAT, cold agglutinin, RBC agglutination on PBS) ^[14] Senior notes: Block A - Introduction to Haematological investigations (CBP, Clotting).pdf (SPE indications, four patterns of SPE interpretation) ^[15] Senior notes: Learning_Points_All_Lectures.txt (Haematology learning points: myeloma workup — SPE, sFLC, BM biopsy) ^[16] Senior notes: Ryan Ho Fundamentals.pdf (BM examination: aspirate vs. trephine technique, indications, MCICM panel) ^[17] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (flow cytometry, IHC, IgH gene rearrangement, clonality determination) ^[18] Senior notes: Ryan Ho Haemtology.pdf, Section 3.6.3 (Myeloma evaluation: skeletal imaging, β2M, serum viscosity, ISS staging) ^[19] Senior notes: Chemical Pathology Data interpretation.pdf (IgM assay interference with calcium) ^[20] Senior notes: Ryan Ho Chemical Path.pdf (paraproteinaemia with ↑IgM causing factitious ↑Ca due to direct interference)

Management of Waldenström Macroglobulinaemia

Treatment Modalities — Detailed

3. First-Line Systemic Therapy

The choice of first-line systemic therapy depends on several factors:

Factor	Considerations
Dominant clinical problem	Hyperviscosity → need rapid IgM reduction; neuropathy → avoid neurotoxic agents; cold AIHA → rituximab-based
Patient fitness	Age, comorbidities, organ function
MYD88 / CXCR4 mutation status	MYD88 mutated → better response to BTK inhibitors; CXCR4 mutated → reduced BTK inhibitor response
Need for rapid response	Chemoimmunotherapy (e.g., bendamustine-rituximab) produces faster, deeper responses; BTK inhibitors produce slower but sustained responses
Patient preference	BTK inhibitors = continuous oral therapy; chemoimmunotherapy = time-limited course

BTK is a kinase downstream of the B-cell receptor (BCR) and the MYD88-IRAK signalling pathway. In WM, the MYD88 L265P mutation constitutively activates this pathway → blocking BTK shuts down the pro-survival NF-κB signalling that drives LPL cell growth.

Agent	Details
Ibrutinib	First-generation BTK inhibitor; FDA-approved for WM (2015). Oral, once daily. Produces rapid IgM reduction. Response rates: ~90% in MYD88-mutated WM, ~60% in MYD88 wild-type. Continue until disease progression or intolerance.
Zanubrutinib	Second-generation BTK inhibitor; more selective for BTK than ibrutinib → fewer off-target effects. Oral, twice daily. Now preferred over ibrutinib in many centres due to better tolerability and at least equivalent efficacy. FDA-approved for WM (2021).
Acalabrutinib	Another second-generation BTK inhibitor; used in some centres but less data specifically in WM compared to zanubrutinib.

Mechanism (from first principles):

"Bruton" → named after Ogden Bruton who described X-linked agammaglobulinaemia (XLA), a disease caused by BTK loss-of-function mutations (no mature B cells produced). So BTK is essential for B-cell survival and signalling.
Inhibiting BTK in WM cells blocks: (a) BCR signalling, (b) MYD88-BTK complex signalling, (c) downstream NF-κB activation → apoptosis of malignant LPL cells.
BTK inhibitors do NOT cause "IgM flare" (unlike rituximab) — they rapidly reduce IgM. This makes them safer for patients with high IgM/hyperviscosity at presentation.

Side effects (ibrutinib > zanubrutinib):

Side Effect	Mechanism
Atrial fibrillation (~5–15% ibrutinib, ~3% zanubrutinib)	Off-target inhibition of cardiac kinases (TEC family); less with zanubrutinib due to greater BTK selectivity
Bleeding (bruising, epistaxis; rarely major haemorrhage)	BTK plays a role in platelet GPIb-IX-V and GPVI signalling → impaired platelet aggregation. Avoid concurrent anticoagulation if possible.
Hypertension	Mechanism not fully understood; more common with ibrutinib
Infections (upper respiratory tract, pneumonia)	B-cell suppression
Diarrhoea, arthralgia	Off-target effects

Contraindications / Cautions:

Concurrent strong CYP3A4 inhibitors or inducers (ibrutinib is CYP3A4-metabolised)
Patients requiring therapeutic anticoagulation with warfarin (bleeding risk); DOACs can be used cautiously
Uncontrolled atrial fibrillation or high bleeding risk

Impact of CXCR4 mutations:

CXCR4-mutated WM patients show slower and less deep responses to BTK inhibitors, with higher residual disease.
These patients may benefit from combination strategies (BTK inhibitor + rituximab) or alternative approaches.

These are time-limited regimens (typically 4–6 cycles), unlike BTK inhibitors (continuous until progression).

Regimen	Components	Key Points
BR (Bendamustine-Rituximab)	Bendamustine (alkylating agent) + Rituximab (anti-CD20 monoclonal antibody)	Widely used first-line; high response rates (~95%); deeper responses than BTK inhibitors (higher rate of VGPR/CR); median PFS ~7 years. Time-limited course (4–6 cycles).
DRC (Dexamethasone-Rituximab-Cyclophosphamide)	Dexamethasone + Rituximab + Cyclophosphamide	Well-tolerated; good for elderly/less fit patients; lower toxicity than BR but less deep responses.
R-CHOP	Rituximab + Cyclophosphamide, Doxorubicin, Vincristine, Prednisone	Historically used; now largely replaced by BR or BTK inhibitors. Reserved for transformation to DLBCL.
VR (Bortezomib-Rituximab)	Bortezomib (proteasome inhibitor) + Rituximab	Bortezomib: inhibition of 26S proteasome → prevent proteolysis of ubiquitin-tagged protein → cytotoxic ^[4]. Useful when avoiding alkylating agents (e.g., young patients concerned about fertility). Also the backbone for WM-associated AL amyloidosis.
Bortezomib-Dexamethasone-Rituximab (BDR)	Bortezomib + Dexamethasone + Rituximab	Active regimen; bortezomib causes rapid IgM reduction (useful in hyperviscosity). Neurotoxicity is a concern (peripheral neuropathy — problematic if anti-MAG neuropathy already present).

Rituximab (anti-CD20) — Detailed:

"Rituxi-" = ritualistic (no meaningful etymology); "-mab" = monoclonal antibody. Targets CD20, which is strongly expressed on WM/LPL cells.
Mechanism: antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), direct apoptosis.
Can be used as monotherapy (for mild disease, neuropathy) or in combination.
Key caution: IgM flare (see callout above) — can worsen hyperviscosity in the first few weeks.

Anti-CD20 monoclonal antibodies (rituximab, obinutuzumab) are also used in CLL as newer agents ^[21]. The principle is the same — targeting the B-cell surface marker CD20.

Bendamustine — Detailed:

"Benda-" from benzimidazole + "mustine" from nitrogen mustard. It is a hybrid molecule combining properties of alkylating agents and purine analogues.
Mechanism: crosslinks DNA (alkylation) + inhibits mitotic checkpoints → apoptosis.
Well tolerated; main toxicities: myelosuppression, infections, nausea.

4. Management of Specific Clinical Syndromes

Step	Action	Rationale
1	Urgent plasmapheresis (1–3 sessions)	Remove IgM from intravascular compartment; ~80% of IgM is intravascular
2	Avoid blood transfusion before plasmapheresis	Transfusing packed RBCs increases viscosity further (adding cellular elements) → can precipitate stroke or organ failure
3	Initiate systemic therapy after stabilisation	BTK inhibitor (preferred — no IgM flare) or chemoimmunotherapy. If rituximab-based regimen chosen, perform plasmapheresis first to lower IgM, then start rituximab.

For relapsed or refractory WM, the principle is to switch class — if the patient progressed on a BTK inhibitor, use chemoimmunotherapy, and vice versa.

Scenario	Preferred Approach
Relapse after BTK inhibitor	Bendamustine-rituximab (BR) or other chemoimmunotherapy
Relapse after chemoimmunotherapy	BTK inhibitor (ibrutinib or zanubrutinib)
Relapse after both	Consider: proteasome inhibitor-based (BDR), venetoclax (BCL-2 inhibitor ^[4]), PI3K inhibitors (idelalisib), clinical trial
Young fit patient with aggressive/refractory disease	Autologous stem cell transplant (ASCT) — consolidative role; provides durable remissions but not curative
Transformation to DLBCL	R-CHOP or equivalent aggressive lymphoma regimen; ASCT if responsive

Allogeneic stem cell transplantation is rarely used in WM (high treatment-related mortality, donor availability issues). Reserved for exceptional cases in young patients with aggressive refractory disease.

Novel and Emerging Agents

Agent	Class	Mechanism	Status in WM
Venetoclax	BCL-2 inhibitor ^[4]	BCL-2 is an anti-apoptotic protein; inhibiting it restores apoptosis in malignant cells	Active in WM; used in relapsed/refractory disease; especially useful in MYD88 wild-type WM
Idelalisib	PI3Kδ inhibitor	Blocks PI3K signalling downstream of BCR	Used in relapsed WM; hepatotoxicity and colitis limit use
Daratumumab	Anti-CD38 monoclonal antibody	CD38 is expressed on WM cells; ADCC, CDC, direct apoptosis	Emerging data; used in combination
CAR-T cell therapy	Chimeric antigen receptor T cells	Engineered T cells targeting B-cell antigens (CD19 or BCMA)	Investigational in WM; more established in DLBCL and MM
Pirtobrutinib	Non-covalent BTK inhibitor	Binds BTK reversibly → active in patients with resistance to covalent BTK inhibitors (ibrutinib, zanubrutinib) due to C481S BTK mutation	Approved for mantle cell lymphoma; investigated in WM

Measure	Rationale
Infection prevention	Immunoparesis (low IgG/IgA) → sinopulmonary infections. Consider prophylactic IVIG if recurrent severe infections with IgG < 4 g/L. Pneumococcal, influenza, COVID-19 vaccination (though response may be blunted).
Transfusion support	Packed RBCs for symptomatic anaemia; platelet transfusion if severe thrombocytopaenia with bleeding. Use blood warmer if cold agglutinins present. For immunocompromised patients requiring irradiated blood products ^[24] — WM patients on intensive chemoimmunotherapy (e.g., fludarabine-based) may need irradiated blood products to prevent transfusion-associated GVHD.
Erythropoiesis-stimulating agents (ESA)	Recombinant EPO for anaemia (particularly if related to BM infiltration rather than haemolysis); reduces transfusion burden.
Thromboprophylaxis	WM confers a modest prothrombotic risk; consider VTE prophylaxis in appropriate clinical contexts (hospitalisation, immobility).
Neuropathic pain management	Gabapentin, pregabalin, duloxetine for anti-MAG neuropathy pain.
Bone health	Unlike myeloma, WM does NOT cause lytic lesions → bisphosphonates are NOT routinely needed.
Cold avoidance	Essential for patients with cryoglobulinaemia or cold AIHA — warm clothing, avoid cold environments, warm IV fluids.
Psychological support	Chronic incurable disease → anxiety, depression common. Support groups, counselling.

Response in WM is assessed by a combination of:

Parameter	Criteria
Serum IgM level	Primary marker of response; measured by SPE (M protein quantification)
Haemoglobin	Improvement indicates reduced BM infiltration / resolved haemolysis
Lymphadenopathy / organomegaly	CT assessment
BM biopsy	Not routinely repeated unless CR is suspected or for clinical trial

Response Category	Definition
Complete response (CR)	IgM normalised; negative immunofixation; no BM infiltration; resolution of all symptoms and organomegaly
Very good partial response (VGPR)	≥90% reduction in IgM; no new symptoms
Partial response (PR)	≥50% reduction in IgM; improvement in symptoms
Minor response (MR)	25–49% reduction in IgM
Stable disease (SD)	< 25% change in IgM
Progressive disease (PD)	≥25% increase in IgM from nadir, confirmed; or new symptoms

Practical point: CR is rare in WM (achieved in < 5% of patients with standard therapy). Most patients achieve PR or VGPR and live with residual disease that is well controlled. This is consistent with the indolent, incurable-but-manageable nature of WM.

Scenario	Management
Smouldering WM	Watch and wait; monitor every 3–6 months
Hyperviscosity emergency	Urgent plasmapheresis → then systemic therapy (BTK inhibitor preferred)
Standard first-line (fit patient)	BTK inhibitor (zanubrutinib preferred) OR bendamustine-rituximab (BR)
Standard first-line (unfit/elderly)	BTK inhibitor monotherapy OR DRC
Anti-MAG neuropathy	Rituximab-based; avoid vincristine/bortezomib; BTK inhibitor if refractory
Cold AIHA	Keep warm; rituximab (steroids do NOT work); BTK inhibitor; complement inhibitor
AL amyloidosis	Bortezomib-based regimen
Bing-Neel (CNS)	BTK inhibitor (crosses BBB); ± intrathecal chemotherapy
Relapsed/refractory	Switch class (BTK ↔ chemoimmunotherapy); venetoclax; ASCT in young fit patients
Transformation to DLBCL	R-CHOP; ASCT if responsive

High Yield Summary — Management of WM

Smouldering WM does not require treatment — only monitoring. Treatment is reserved for symptomatic WM with attributable end-organ damage.
Plasmapheresis is the emergency treatment for hyperviscosity — removes intravascular IgM rapidly. It is a bridge to definitive systemic therapy, not definitive treatment itself.
BTK inhibitors (zanubrutinib, ibrutinib) are the dominant first-line agents — they exploit the MYD88-BTK signalling dependency of WM cells. Zanubrutinib preferred due to fewer off-target effects (less AF, less bleeding).
Bendamustine-Rituximab (BR) is the main chemoimmunotherapy alternative — time-limited, deeper responses, but more myelosuppression.
Rituximab causes IgM flare — pre-treat with plasmapheresis if IgM > 40 g/L or viscosity > 3.5 cp. BTK inhibitors do NOT cause IgM flare.
Cold AIHA: steroids do NOT work (complement-mediated, not Fc receptor-mediated). Use rituximab, BTK inhibitors, keep warm.
Anti-MAG neuropathy: avoid neurotoxic agents (vincristine, bortezomib). Use rituximab-based therapy.
WM is generally incurable — aim is disease control and quality of life. CR is rare (< 5%); most patients achieve PR/VGPR and live with controlled disease.
Response is monitored primarily by serial serum IgM levels (SPE).
Supportive care includes infection prevention (IVIG if recurrent infections), blood warmers for cold agglutinins, ESAs for anaemia, and neuropathic pain management.

Active Recall - Management of Waldenström Macroglobulinaemia

References

^[1] Senior notes: Ryan Ho Haemtology.pdf, Section 3.6.4 (Waldenström Macroglobulinaemia — diagnostic criteria, clinical presentation, treatment) ^[2] Lecture slides: Block A - Generalised Lymphadenopathy_ Differential diagnosis and principle of management.pdf (indolent lymphoma classification: LPL and WM; treatment principles of lymphomas) ^[4] Senior notes: Block A - An old man with bone pain and anaemia_ multiple myeloma; monoclonal gammopathy.pdf (MGUS/SMM/MM spectrum; proteasome inhibitors: bortezomib mechanism; novel agents: venetoclax, daratumumab, CAR-T) ^[13] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (cold AIHA: steroids not effective; keep warm; treatment principles of AIHA) ^[21] Senior notes: Maksim Medicine Notes.pdf (CLL management: watch and wait for early stage; rituximab, ibrutinib, venetoclax as newer agents) ^[22] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (CML not curable, controlled with drugs; monitoring molecular response) ^[23] Senior notes: Block A – Nephrology Data Interpretation.pdf (plasmapheresis in Goodpasture syndrome to remove circulating antibodies) ^[24] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (irradiated blood products for immunocompromised patients)

Complications of Waldenström Macroglobulinaemia

These are complications caused by the disease itself and are the primary reasons treatment is initiated.

This is the signature complication of WM, occurring in ~10–30% of patients. It arises because IgM is a pentamer (~970 kDa) — even modest serum concentrations cause disproportionate increases in viscosity.

Complication	Pathophysiology	Clinical Consequence
Retinal haemorrhage / visual loss	Hyperviscous blood causes sludging in retinal microcirculation → venous engorgement → vessel rupture → haemorrhage. Fundus findings: dilated, segmented, tortuous, "sausage link" retinal veins ± haemorrhage, exudate, papilloedema ^[1]	Permanent visual loss if untreated; the retina is exquisitely sensitive to perfusion changes
Cerebrovascular events	Sludging in cerebral microvasculature → ischaemia → TIA or stroke. Also increased risk of intracerebral haemorrhage from vessel wall damage	Confusion → coma → death if viscosity not urgently reduced
Cardiac complications	Increased plasma volume + increased viscosity → increased afterload and preload → high-output cardiac failure. Expanded plasma volume also causes haemodilution → worsens anaemia → further cardiac stress	Dyspnoea, peripheral oedema, pulmonary oedema
Mucosal bleeding	Distended mucosal capillaries rupture under increased intravascular pressure; IgM also coats platelets (impairs adhesion/aggregation) and interferes with clotting factors (especially vWF and fibrinogen) → multifactorial coagulopathy	Epistaxis, gingival bleeding, GI bleeding

Key point: Hyperviscosity syndrome is a medical emergency requiring urgent plasmapheresis. If untreated, it can lead to irreversible visual loss, stroke, and death.

Complication	Pathophysiology	Clinical Consequence
Anaemia (most common haematological complication)	Multifactorial: (1) BM infiltration by LPL cells → crowding out of normal erythroid precursors; (2) Cold AIHA → complement-mediated RBC destruction; (3) Haemodilution → increased plasma volume from IgM osmotic effect; (4) Cytokine-mediated suppression of erythropoiesis (IL-6, TNF)	Fatigue, dyspnoea on exertion, palpitations, pallor; may require transfusion or ESA support
Thrombocytopaenia	BM infiltration replacing megakaryocytes	Bleeding tendency (petechiae, bruising); rarely severe in WM
Neutropaenia	BM infiltration; also treatment-related (chemoimmunotherapy)	Infection susceptibility

C. Immune Complications

Complication	Pathophysiology
Recurrent sinopulmonary infections	The malignant clone suppresses normal B-cell function → immunoparesis (reduced polyclonal IgG and IgA). This is functionally equivalent to secondary hypogammaglobulinaemia. Patients cannot mount adequate antibody responses to encapsulated bacteria (Streptococcus pneumoniae, Haemophilus influenzae) or other respiratory pathogens.
Herpes zoster reactivation	Disease-related and treatment-related immunosuppression (especially with BTK inhibitors, rituximab, or chemotherapy) impairs T-cell surveillance of latent VZV

Infection is a major cause of morbidity and mortality in WM. Patients with recurrent severe infections and IgG < 4 g/L should be considered for prophylactic IVIG replacement.

Aspect	Detail
Mechanism	Monoclonal IgM acts as a cold agglutinin — it binds RBC surface antigens (typically the "I" antigen) at temperatures below 37°C. This activates the classical complement pathway (C1q → C4 → C2 → C3). When blood returns to the warm core, IgM dissociates but C3b/C3d remains fixed on the RBC surface → (a) intravascular haemolysis (via membrane attack complex if complement fully activated); (b) extravascular haemolysis in the liver (hepatic Kupffer cells recognise C3b via complement receptors).
Clinical significance	Worsens anaemia; episodes triggered by cold exposure; haemoglobinuria; fatigue; jaundice
Diagnostic finding	DAT positive for C3d (not IgG) ^[13]. This distinguishes cold AIHA from warm AIHA (DAT positive for IgG). RBC agglutination on peripheral blood smear — as seen in cold agglutinin diseases ^[13]
Treatment implication	Steroids do NOT work in cold AIHA ^[13] — complement-mediated destruction is not suppressed by steroids. Use rituximab-based therapy, BTK inhibitors, or complement inhibitors (sutimlimab).

Aspect	Detail
Mechanism	Monoclonal IgM precipitates at cold temperatures (Type I cryoglobulinaemia) → deposits in small vessels of skin, kidneys, nerves → immune complex-mediated vasculitis (complement activation, neutrophil recruitment)
Complications	Palpable purpura (lower limbs), skin ulceration, digital ischaemia/gangrene, membranoproliferative glomerulonephritis (MPGN), peripheral neuropathy (vasculitic neuropathy — distinct from anti-MAG neuropathy)
Renal involvement	Cryoglobulin-related MPGN → proteinuria, haematuria, renal impairment. Renal biopsy shows subendothelial deposits with characteristic "fingerprint" pattern on electron microscopy

Complication	Pathophysiology	Clinical Features
Anti-MAG peripheral neuropathy (~20–25%)	Monoclonal IgM binds myelin-associated glycoprotein (MAG) on Schwann cells → complement-mediated demyelination of peripheral nerves, predominantly in distal segments	Slowly progressive distal symmetric sensorimotor polyneuropathy; sensory > motor; gait unsteadiness; impaired fine motor skills. NCS: demyelinating, sensory > motor ^[1]
Bing-Neel syndrome (rare, < 1%)	Direct infiltration of CNS (leptomeninges and/or brain parenchyma) by malignant LPL cells. Named after Bing and Neel who first described CNS involvement in macroglobulinaemia (1936)	Headache, confusion, cranial nerve palsies, ataxia, seizures, myelopathy. MRI: leptomeningeal enhancement, periventricular lesions. CSF: clonal B cells on flow cytometry
Hyperviscosity-related CNS events	Sludging in cerebral microvasculature → ischaemia/haemorrhage	TIA, stroke, encephalopathy, coma

Renal involvement is uncommon in WM compared to multiple myeloma — because intact IgM is too large to be filtered by the glomerulus (unlike free light chains in myeloma).

Renal Complication	Pathophysiology
Light chain cast nephropathy	If the WM clone produces excess free light chains, these are filtered by the glomerulus and precipitate with Tamm-Horsfall protein in the distal tubules → tubular obstruction → acute kidney injury. Cast nephropathy is the most common cause of kidney failure in MM; casts are intensely eosinophilic, lamellated, surrounded by macrophages and giant cells ^[23]. The same mechanism can (rarely) occur in WM.
AL amyloidosis	Monoclonal light chains misfold into amyloid fibrils → deposit in glomeruli and tubular basement membranes → nephrotic syndrome, progressive CKD. Congo red stain positive; electron microscopy shows non-branching fibrils ^[10]
Light and heavy chain deposition disease (LCDD/HCDD)	Non-amyloid deposition of monoclonal light or heavy chains in glomerular and tubular basement membranes → nodular glomerulosclerosis → nephrotic syndrome, renal impairment. Differential diagnosis includes light and heavy chain deposition disease — complication of monoclonal gammopathy ^[23]
Cryoglobulinaemic glomerulonephritis	Type I cryoglobulins (monoclonal IgM) deposit in glomeruli → MPGN pattern → haematuria, proteinuria, renal impairment
IgM deposition disease	Direct deposition of intact IgM in glomerular capillaries → thickened capillary walls → proteinuria. Rare but specific to IgM-producing disorders

Mechanism	Explanation
Platelet dysfunction	IgM coats platelet surfaces → impairs GPIb-IX-V and GPIIb-IIIa-mediated adhesion and aggregation → qualitative platelet defect. Bleeding time is prolonged even with normal platelet count.
Acquired von Willebrand disease	IgM binds vWF → accelerated clearance or functional inhibition of vWF → reduced vWF:Ag and vWF:RCo → mucocutaneous bleeding pattern
Clotting factor interference	IgM interacts with fibrinogen and other clotting factors → prolonged thrombin time, occasionally prolonged aPTT

The bleeding tendency in WM is multifactorial and cannot be attributed to a single mechanism. This makes it more challenging to manage than bleeding in isolated coagulopathies.

Paraneoplastic pemphigus (PNP) is a rare but important association:

Paraneoplastic pemphigus can be associated with: Non-Hodgkin lymphoma, chronic lymphocytic leukaemia, Castleman disease, thymoma, Waldenström macroglobulinemia, solid organ tumours ^[25].

Aspect	Detail
Mechanism	Autoantibodies (including anti-envoplakin, anti-periplakin) produced by or induced by the lymphoproliferative neoplasm target desmosomal proteins in the skin and mucosal epithelium → suprabasal acantholysis + interface dermatitis
Clinical features	Severe, intractable stomatitis (mouth ulcers) + polymorphous skin eruption (blisters, erosions, lichenoid lesions). Bronchiolitis obliterans (constrictive small airway disease) is a dreaded pulmonary complication of PNP with poor prognosis ^[25]
Prognosis	Poor; mortality often from respiratory failure due to bronchiolitis obliterans rather than the primary lymphoma

Other skin complications include:

Cutaneous infiltration by LPL → skin-coloured papules or nodules
Schnitzler syndrome — chronic urticaria + monoclonal IgM + systemic inflammation (fever, bone pain, elevated acute phase reactants). A rare but characteristic syndrome that may precede overt WM by years.
Sweet syndrome (acute febrile neutrophilic dermatosis) — paraneoplastic; painful erythematous plaques/nodules

Every WM therapy has its own toxicity profile. Understanding these from first principles helps in anticipating, preventing, and managing them.

Complication	Mechanism	Notes
Atrial fibrillation (~5–15% ibrutinib; ~3% zanubrutinib)	Off-target inhibition of cardiac kinases (TEC, ITK) disrupts atrial cardiomyocyte calcium handling and PI3K-Akt signalling	More common with ibrutinib (less selective). Monitor ECG. May require rate/rhythm control. Consider switching to zanubrutinib if AF develops on ibrutinib.
Bleeding (bruising, epistaxis; rarely major)	BTK mediates platelet GPVI and GPIb-IX signalling → inhibition impairs platelet aggregation	Avoid concurrent warfarin. Withhold BTK inhibitor perioperatively (3–7 days before surgery).
Hypertension	Unclear mechanism; possibly related to off-target vascular kinase inhibition	Monitor BP regularly. Treat with standard antihypertensives.
Infections (upper respiratory, pneumonia, UTI)	B-cell suppression; also impaired innate immunity (BTK expressed in macrophages/neutrophils)	Invasive fungal infections (aspergillosis) reported; consider prophylaxis in high-risk patients.
Diarrhoea, arthralgia, myalgia	Off-target effects	Usually manageable; dose reduction if needed

Complication	Mechanism
IgM flare (paradoxical transient IgM increase)	Mechanism debated — possibly B-cell lysis releasing preformed IgM, or transient upregulation of Ig secretion. Can precipitate or worsen hyperviscosity.
Infusion reactions (fever, chills, rigors, hypotension, bronchospasm)	Cytokine release from B-cell lysis during first infusion; premedicate with paracetamol, antihistamine, ± hydrocortisone
Hepatitis B reactivation	Rituximab depletes B cells (including memory B cells controlling HBV) → loss of immune surveillance → HBV reactivation, potentially fulminant hepatitis. Pre-treatment HBV screening is mandatory; HBsAg+ patients need concurrent antiviral prophylaxis (entecavir or tenofovir). Hep B/C serology should be checked pre-treatment ^[3]
Progressive multifocal leukoencephalopathy (PML)	Extremely rare; JC virus reactivation due to profound immunosuppression → demyelination of CNS white matter. Fatal in most cases.
Late-onset neutropaenia	Occurs weeks to months after rituximab; mechanism incompletely understood (disrupted B-T cell interactions affecting granulopoiesis)
Hypogammaglobulinaemia	Sustained B-cell depletion → reduced Ig production → increased infection risk

Complication	Mechanism
Myelosuppression (neutropaenia, thrombocytopaenia, anaemia)	Alkylating agents damage rapidly dividing cells including normal haematopoietic precursors → pancytopaenia
Febrile neutropaenia	Severe neutropaenia (ANC < 0.5 × 10⁹/L) + fever → medical emergency requiring immediate blood cultures and empirical broad-spectrum antibiotics within one hour ^[15]
Tumour lysis syndrome (TLS)	Rapid cell death releases intracellular contents → hyperuricaemia, hyperkalaemia, hyperphosphataemia, hypocalcaemia → AKI, cardiac arrhythmias. TLS prophylaxis: IV fluid + allopurinol (or febuxostat) ^[21]. More relevant in high tumour burden disease.
Infections (bacterial, viral, fungal)	Immunosuppression from chemotherapy; opportunistic infections including Pneumocystis jirovecii pneumonia (PJP) — consider co-trimoxazole prophylaxis with fludarabine-based or intensive regimens
Secondary malignancies	Alkylating agents (cyclophosphamide, bendamustine) → DNA damage → increased long-term risk of MDS and secondary AML (typically therapy-related, t-MDS/AML)
Infertility	Alkylating agents are gonadotoxic. Consider fertility preservation (sperm banking, oocyte cryopreservation) in young patients before starting treatment.
Nausea and vomiting	Direct chemotherapy toxicity on GI mucosa and CTZ stimulation; manage with 5-HT3 antagonists (ondansetron), NK1 antagonists, dexamethasone

Complication	Mechanism
Peripheral neuropathy	Bortezomib: inhibition of 26S proteasome ^[4] → accumulation of misfolded proteins in dorsal root ganglia neurons → axonal degeneration. Dose-limiting toxicity. Problematic in WM patients who already have anti-MAG neuropathy. Subcutaneous administration reduces neuropathy risk compared to IV.
Thrombocytopaenia (cyclical)	Proteasome inhibition in megakaryocytes impairs platelet production; characteristically cyclical — nadir at day 11, recovery by day 21 of each cycle
Herpes zoster reactivation	Proteasome inhibition impairs T-cell function → VZV reactivation. Prophylactic aciclovir/valaciclovir is mandatory during bortezomib treatment.
GI toxicity (diarrhoea, constipation, nausea)	Autonomic neuropathy from proteasome inhibition in enteric nervous system

This is the most feared long-term complication of WM and all indolent lymphomas.

Aspect	Detail
What is transformation?	The indolent LPL clone acquires additional genetic hits → evolves into an aggressive high-grade lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL). This is analogous to Richter transformation in CLL (transformation of CLL/SLL into DLBCL or HL) ^[21] and the transformation of other indolent lymphomas.
Incidence	~2–10% of WM patients over their lifetime; annual rate ~0.5–1%
Risk factors	Longer disease duration; prior treatment (especially alkylating agents); del(6q); complex karyotype; high β2-microglobulin
How to suspect it	Sudden clinical deterioration: rapidly enlarging lymph nodes, new B symptoms (fever, drenching night sweats, weight loss > 10%), markedly elevated LDH, new extranodal masses. High-grade NHL: rapidly growing masses with prominent systemic B symptoms ^[3]
How to confirm it	Tissue biopsy (excisional lymph node biopsy preferred) showing large B-cell morphology (DLBCL). PET-CT shows intense FDG uptake (SUVmax typically > 10) in focal areas vs. low-grade uptake in untransformed WM.
Treatment	R-CHOP (Rituximab, Cyclophosphamide, Hydroxydaunorubicin/Adriamycin/Doxorubicin, Oncovin/Vincristine, Prednisolone ^[21]) or equivalent aggressive lymphoma regimen. Autologous HSCT if chemoresponsive. Prognosis is significantly worse than untransformed WM.
Prognosis after transformation	Median survival ~1–2 years; much worse than de novo DLBCL

Transformation — The Red Flag Signs

If a patient with known WM suddenly develops:

Rapidly enlarging lymph nodes
New or worsening B symptoms
Dramatically rising LDH
Focal intense PET-CT uptake

→ Suspect histological transformation to DLBCL. This requires urgent tissue biopsy and a change in treatment strategy to aggressive lymphoma regimens. Do NOT continue indolent lymphoma therapy if transformation is confirmed.

4. Other Long-Term Complications

Aspect	Detail
Mechanism	The monoclonal light chains produced by the LPL clone misfold into β-pleated sheet fibrils → deposit in tissues as amyloid → organ dysfunction. AL amyloidosis can arise as a complication of myeloma in 10% of cases ^[10]; similarly, it can complicate WM.
Affected organs	Heart (restrictive cardiomyopathy), kidneys (nephrotic syndrome), nerves (painful sensorimotor + autonomic neuropathy), GI tract (malabsorption, hepatomegaly), tongue (macroglossia)
Diagnosis	Congo red stain → salmon pink colour → apple-green birefringence under polarised light. Electron microscopy shows non-branching fibrils in the extracellular compartment ^[10]. Mass spectrometry confirms AL (light chain) type.
Prognosis	Significantly worsens prognosis of WM, especially if cardiac involvement (median survival < 1 year without treatment in advanced cardiac amyloidosis)

Category	Key Complications
IgM-mediated	Hyperviscosity syndrome (visual loss, stroke, bleeding, heart failure); cold AIHA; cryoglobulinaemia (vasculitis, GN, neuropathy); acquired coagulopathy; neuropathy (anti-MAG)
Tumour infiltration	Cytopenias (anaemia, thrombocytopaenia, neutropaenia); hepatosplenomegaly; lymphadenopathy; Bing-Neel syndrome
Immune	Immunoparesis → recurrent infections; hypogammaglobulinaemia; autoimmune cytopenias
Renal	Cast nephropathy (rare); AL amyloidosis; LCDD; cryoglobulinaemic GN; IgM deposition disease
Skin	Paraneoplastic pemphigus; Schnitzler syndrome; cutaneous LPL infiltration; Sweet syndrome
Transformation	DLBCL (~2–10% lifetime risk); poor prognosis
Treatment-related	BTK inhibitor (AF, bleeding, infections); rituximab (IgM flare, HBV reactivation, PML); chemo (myelosuppression, febrile neutropaenia, TLS, secondary malignancy, infertility); bortezomib (neuropathy, VZV reactivation)
Long-term	AL amyloidosis; secondary MDS/AML; chronic infections; VTE

High Yield Summary — Complications of WM

Hyperviscosity syndrome is the signature complication — emergency requiring urgent plasmapheresis. Can cause visual loss, stroke, cardiac failure, and death.
Cold AIHA — IgM cold agglutinin → complement-mediated haemolysis. DAT positive for C3d. Steroids do NOT work. Treat with rituximab or BTK inhibitors.
Anti-MAG neuropathy — slowly progressive distal demyelinating sensorimotor polyneuropathy. Avoid neurotoxic drugs (bortezomib, vincristine).
Immunoparesis → recurrent infections — a major cause of morbidity and mortality. Consider IVIG prophylaxis if IgG < 4 g/L with recurrent infections.
Transformation to DLBCL — the most feared long-term complication (~2–10% lifetime risk). Suspect if rapidly growing nodes, new B symptoms, rising LDH. Requires aggressive R-CHOP-type therapy.
AL amyloidosis — monoclonal light chains deposit as amyloid in heart, kidneys, nerves, GI. Significantly worsens prognosis.
Treatment complications: BTK inhibitors cause AF and bleeding; rituximab causes IgM flare and HBV reactivation; chemotherapy causes myelosuppression, TLS, secondary malignancies; bortezomib causes neuropathy and VZV reactivation.
Paraneoplastic pemphigus is a rare but important skin complication with poor prognosis (bronchiolitis obliterans).
Renal complications are uncommon in WM (< 3%) compared to myeloma, because intact IgM is too large to be filtered by the glomerulus.
Unlike myeloma, WM does NOT cause lytic bone lesions, hypercalcaemia, or osteoclast-mediated bone destruction.

Active Recall - Complications of Waldenström Macroglobulinaemia

References

^[1] Senior notes: Ryan Ho Haemtology.pdf, Section 3.6.4 (Waldenström Macroglobulinaemia — clinical presentation, hyperviscosity, neuropathy, cryoglobulinaemia) ^[3] Senior notes: Adrian Lui Pediatrics Notes.pdf, Section 11.1.2 (Lymphoma — NHL high-grade features, pre-treatment investigations including HBV serology) ^[4] Senior notes: Block A - An old man with bone pain and anaemia_ multiple myeloma; monoclonal gammopathy.pdf (proteasome inhibitor mechanism; paraproteinaemia DDx including WM and AL amyloidosis) ^[10] Senior notes: Block A - Hematology Data Interpretation.pdf (AL amyloidosis: Congo red stain, electron microscopy, immunoparesis; relationship between AL amyloidosis and MM) ^[13] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (cold AIHA: DAT C3d, steroids not effective; RBC agglutination on PBS) ^[15] Senior notes: Learning_Points_All_Lectures.txt (febrile neutropaenia as medical emergency; broad-spectrum antibiotics within one hour) ^[21] Senior notes: Maksim Medicine Notes.pdf (CLL Richter transformation; NHL management R-CHOP; TLS prophylaxis) ^[23] Senior notes: Block A – Nephrology Data Interpretation.pdf (cast nephropathy pathophysiology; light and heavy chain deposition disease as complication of monoclonal gammopathy) ^[25] Lecture slides: Derm General Clerkship 2026 Part2.pdf (paraneoplastic pemphigus associations including WM; bronchiolitis obliterans)

High Yield Summary

WM = BM lymphoplasmacytic lymphoma (LPL) + IgM M protein of any size. The malignant cell is a post-GC B cell that has undergone somatic hypermutation but NOT class switching → stuck producing IgM.
MYD88 L265P mutation is found in >90% of WM — constitutive NF-κB activation → cell survival + proliferation. Key molecular marker distinguishing WM from other IgM-producing lymphomas.
IgM is a pentamer (~970 kDa) → causes hyperviscosity syndrome far more readily than IgG/IgA. Hyperviscosity is the hallmark complication of WM.
Two mechanisms of disease: (a) IgM protein effects (hyperviscosity, autoantibody activity [anti-MAG neuropathy, cold AIHA], cryoglobulinaemia, tissue deposition, coagulopathy, immunoparesis); (b) Direct tumour infiltration (BM → cytopenias; LN → lymphadenopathy; liver/spleen → hepatosplenomegaly).
Fundoscopy is critical — "sausage-shaped" retinal veins + haemorrhages = hyperviscosity → urgent plasmapheresis.
WM vs. Myeloma: WM has NO lytic bone lesions, IgM paraprotein, lymphadenopathy/hepatosplenomegaly present, MYD88+. Myeloma has lytic bone lesions, IgG/IgA paraprotein, no lymphadenopathy, MYD88−.
Spectrum: IgM MGUS → Smouldering WM → Symptomatic WM. Only symptomatic WM requires treatment.
Rare in Hong Kong/Asians (much more common in Caucasians); median age 70, M > F (60%).

High Yield Summary — Differential Diagnosis of WM

Monoclonal IgM is not WM by itself. The DDx of monoclonal IgM includes IgM MGUS, smouldering WM, CLL, marginal zone lymphoma, IgM myeloma, AL amyloidosis, and heavy chain disease.
BM biopsy is essential to distinguish WM (LPL morphology) from CLL (small lymphocytes, CD5+/CD23+), MZL (marginal zone morphology), and IgM MM (plasma cell sheets with lytic lesions).
MYD88 L265P is the key molecular distinguisher — positive in >90% of WM, rare in MZL, CLL, IgM MM.
No lytic bone lesions in WM — if present, think IgM myeloma.
Hyperviscosity DDx includes PV (cellular viscosity from high Hct), hyperleukocytosis (blast sludging), and rarely IgA/IgG3 myeloma — but WM is the most common cause of paraprotein-related hyperviscosity.
Neuropathy + IgM = think WM/MGUS with anti-MAG antibodies; distinguish from POEMS (IgG/IgA λ), AL amyloidosis, CIDP, and diabetic neuropathy.
Cold AIHA + monoclonal IgM = WM-associated CAD vs. primary CAD vs. infection-associated (Mycoplasma, EBV).
The spectrum: IgM MGUS → Smouldering WM → Symptomatic WM mirrors the MGUS → SMM → MM spectrum for IgG/IgA paraproteins.

High Yield Summary — Diagnosis of WM

Diagnostic criteria (ALL must be met): (a) IgM monoclonal gammopathy of any size; (b) ≥10% BM lymphoplasmacytic infiltrate in intertrabecular pattern; (c) Typical immunophenotype (CD19+, CD20+ strong, CD5−, CD10−, CD23−).
MYD88 L265P (>90% of WM) is not in the formal criteria but is indispensable for confirming diagnosis and distinguishing WM from mimics (MZL, IgM MM, CLL).
SPE → IFE → BM biopsy is the core diagnostic pathway for any suspected monoclonal gammopathy.
Four SPE patterns: normal, pan-immunoparesis, polyclonal hypergammaglobulinaemia (reactive — do NOT refer to haematology), and paraprotein ± immunoparesis.
Serum viscosity should be measured if IgM > 5 g/dL or symptoms of hyperviscosity. Symptomatic at ≥4 cp.
Fundoscopy is essential — sausage-link retinal veins = hyperviscosity emergency.
No lytic bone lesions in WM — unlike myeloma. If lytic lesions present with IgM, think IgM MM.
Haemolysis screen (LDH, haptoglobin, bilirubin, DAT) if cold AIHA suspected — DAT positive for C3d (not IgG) in cold AIHA.
IPSSWM uses 5 factors: age > 65, Hb ≤ 11.5, Plt ≤ 100, β2M > 3, IgM > 70.
IgM can cause assay interference — factitious hypercalcaemia, phosphate interference, spurious MCV elevation from agglutination.

High Yield Summary — Management of WM

Smouldering WM does not require treatment — only monitoring. Treatment is reserved for symptomatic WM with attributable end-organ damage.
Plasmapheresis is the emergency treatment for hyperviscosity — removes intravascular IgM rapidly. It is a bridge to definitive systemic therapy, not definitive treatment itself.
BTK inhibitors (zanubrutinib, ibrutinib) are the dominant first-line agents — they exploit the MYD88-BTK signalling dependency of WM cells. Zanubrutinib preferred due to fewer off-target effects (less AF, less bleeding).
Bendamustine-Rituximab (BR) is the main chemoimmunotherapy alternative — time-limited, deeper responses, but more myelosuppression.
Rituximab causes IgM flare — pre-treat with plasmapheresis if IgM > 40 g/L or viscosity > 3.5 cp. BTK inhibitors do NOT cause IgM flare.
Cold AIHA: steroids do NOT work (complement-mediated, not Fc receptor-mediated). Use rituximab, BTK inhibitors, keep warm.
Anti-MAG neuropathy: avoid neurotoxic agents (vincristine, bortezomib). Use rituximab-based therapy.
WM is generally incurable — aim is disease control and quality of life. CR is rare (< 5%); most patients achieve PR/VGPR and live with controlled disease.
Response is monitored primarily by serial serum IgM levels (SPE).
Supportive care includes infection prevention (IVIG if recurrent infections), blood warmers for cold agglutinins, ESAs for anaemia, and neuropathic pain management.

High Yield Summary — Complications of WM

Hyperviscosity syndrome is the signature complication — emergency requiring urgent plasmapheresis. Can cause visual loss, stroke, cardiac failure, and death.
Cold AIHA — IgM cold agglutinin → complement-mediated haemolysis. DAT positive for C3d. Steroids do NOT work. Treat with rituximab or BTK inhibitors.
Anti-MAG neuropathy — slowly progressive distal demyelinating sensorimotor polyneuropathy. Avoid neurotoxic drugs (bortezomib, vincristine).
Immunoparesis → recurrent infections — a major cause of morbidity and mortality. Consider IVIG prophylaxis if IgG < 4 g/L with recurrent infections.
Transformation to DLBCL — the most feared long-term complication (~2–10% lifetime risk). Suspect if rapidly growing nodes, new B symptoms, rising LDH. Requires aggressive R-CHOP-type therapy.
AL amyloidosis — monoclonal light chains deposit as amyloid in heart, kidneys, nerves, GI. Significantly worsens prognosis.
Treatment complications: BTK inhibitors cause AF and bleeding; rituximab causes IgM flare and HBV reactivation; chemotherapy causes myelosuppression, TLS, secondary malignancies; bortezomib causes neuropathy and VZV reactivation.
Paraneoplastic pemphigus is a rare but important skin complication with poor prognosis (bronchiolitis obliterans).
Renal complications are uncommon in WM (< 3%) compared to myeloma, because intact IgM is too large to be filtered by the glomerulus.
Unlike myeloma, WM does NOT cause lytic bone lesions, hypercalcaemia, or osteoclast-mediated bone destruction.

Waldenström Macroglobulinaemia

1. Definition

2. Epidemiology

3. Anatomy and Function: The Normal B-Cell Maturation Pathway

Normal B-Cell Development (Simplified)

Why IgM Matters: Structure of IgM

4. Aetiology and Risk Factors

4.1 Genetic Factors

MYD88 L265P Mutation

CXCR4 Mutations

Familial Predisposition

4.2 Environmental / Infectious Factors

4.3 Precursor Conditions (The Spectrum of Monoclonal IgM)

5. Pathophysiology

Mechanism 1: Effects of the Monoclonal IgM Protein in the Blood

Mechanism 2: Direct Tissue Infiltration by Malignant LPL Cells

6. Classification

6.1 Within the WHO/ICC Classification of Haematolymphoid Neoplasms (2022 WHO 5th Edition / ICC 2022)

6.2 Within the Spectrum of Plasma Cell Dyscrasias / Monoclonal Gammopathies

7. Clinical Features

Important Context

7.1 Symptoms

A. Constitutional Symptoms

B. Symptoms Due to IgM M Protein ("Paraprotein-Related")

i. Hyperviscosity Syndrome (~10–30% of WM patients)

ii. Peripheral Neuropathy (~20–25% of WM patients)

iii. Cold-Related Symptoms

iv. Bleeding Symptoms

v. Infection Susceptibility

C. Symptoms Due to Tumour (LPL) Infiltration

D. Rare / Special Symptoms

7.2 Signs

A. General Examination

B. Head and Neck

C. Abdominal Examination

D. Peripheral Examination

E. Cardiovascular

8. Summary of Clinical Features by Pathophysiological Mechanism

9. Risk Factors for Progression (from IgM MGUS / SWM to WM)

Active Recall - Waldenström Macroglobulinaemia (Definition, Epidemiology, Aetiology, Pathophysiology, Clinical Features)

References

Approach to Differential Diagnosis

Organising Framework

Tier 1: Differential Diagnosis of Monoclonal IgM (The Core DDx)

Tier 2: Differential Diagnosis by Dominant Clinical Syndrome

A. Differential Diagnosis of Hyperviscosity Syndrome

B. Differential Diagnosis of Paraprotein-Associated Peripheral Neuropathy

C. Differential Diagnosis of Cold AIHA / Cold Agglutinin Disease (CAD)

D. Differential Diagnosis of Cytopenias (Especially Anaemia) in the Elderly

Tier 3: Other B-Cell Lymphoproliferative Disorders

Summary Table: Key Differential Diagnoses and How to Distinguish Them

Clinical Reasoning: When Should WM Be Favoured Over Its Mimics?

Active Recall - Differential Diagnosis of Waldenström Macroglobulinaemia

1. Diagnostic Criteria

Formal Diagnostic Criteria (IWWM / WHO-aligned)

Characteristic Immunophenotype of WM/LPL

Role of MYD88 L265P Mutation

When Is Treatment Indicated? (Symptomatic vs. Asymptomatic WM)

2. Diagnostic Algorithm

3. Investigation Modalities — Detailed Interpretation

3.1 Confirming the Paraprotein

A. Serum Protein Electrophoresis (SPE)

B. Serum Immunofixation Electrophoresis (IFE)

C. Quantitative Serum Immunoglobulins (IgG, IgA, IgM)

D. Serum Free Light Chains (sFLC) and κ:λ Ratio

E. Urine Investigations

3.2 Bone Marrow Biopsy (The Definitive Diagnostic Investigation)

3.3 Assessing Disease Burden and Complications

A. Complete Blood Count with Differential

B. Peripheral Blood Smear (PBS)

C. Biochemistry Panel

D. Haemolysis Screen (If Cold AIHA Suspected)

E. Serum Viscosity

F. Cryoglobulin Screen

G. Neuropathy Workup (If Neuropathy Present)

3.4 Imaging

3.5 Fundoscopy

3.6 Additional Specialised Investigations

4. Prognostic Scoring: International Prognostic Scoring System for WM (IPSSWM)

5. Summary: Investigation Roadmap