Waldenström Macroglobulinaemia, MGUS & Hyperviscosity Syndrome

Meet the patient

A 68-year-old man arrives at 4am with a nose that will not stop bleeding, vision he describes as "looking through water", and a stagger that started at dinner. He is pale, his pulse is full, and the registrar reaches for a cannula and two units of blood. That reach is the single most dangerous reflex in this disease. The fundus, when you finally look at it, tells the whole story: the retinal veins are beaded into sausage-strings, scattered with flame haemorrhages and blurred at the disc margins.[2]

Two questions decide the next hour, and they decide every IgM-gammopathy stem you will ever meet: is this hyperviscosity? (the fundus and a serum viscosity answer within the hour) and have I emptied the vessel before I treat the clone? (plasmapheresis first, definitive chemotherapy second — never the other way round, and never a transfuse-first reflex). Hold those two and the rest of the page slots into place.[2]

One clone, one pentamer, three faces

The IgM gammopathies are not three diseases — they are one clone read at three levels of burden. A single post-germinal-centre B cell begins to secrete monoclonal IgM; what you call it depends only on how much IgM it makes, how much marrow it has colonised, and whether it has started to harm the patient. Read it like a tumour-burden dial, with the WHO and International Workshop for Waldenstrom Macroglobulinaemia drawing the lines.[1]

The spectrum every final-prof candidate must reproduce:[1]

[1]

The numbers that anchor every stem:[1]

[1]

[1]

MGUS is benign — but you never discharge it

MGUS is the haematology patient you never truly discharge — not because they are unwell, but because the risk never clocks out. The criteria are three numbers, all benign: a serum M-protein under 30 g/L, marrow plasma cells under 10 percent, and no CRAB (no hyperCalcaemia, Renal failure, Anaemia, or Bone lesions). It is common — present in over 3 percent of people over 50 and over 5 percent of those over 70 — with a slight male predominance and two to three times the prevalence in Black populations. The job is not to treat it; the job is to risk-stratify it and watch it forever.[1]

The progression risk is the teaching point examiners love: it runs at about 1 percent per year, lifelong, and constant. A patient with stable MGUS for 30 years still carries roughly a 1 percent risk in year 31 — which is why discharge is the wrong word and "lifelong monitoring" is the right one. For IgM MGUS specifically, the rate is a little higher (about 1.5 to 2 percent per year) and the destination is more often Waldenstrom than myeloma.[1]

Risk-stratify every MGUS with the International Myeloma Working Group (IMWG) model — three adverse factors, each worth one point:[1]

• M-protein at least 15 g/L.
• Non-IgG isotype (IgA or IgM — note that IgM MGUS scores this point automatically).
• Abnormal serum free-light-chain ratio (under 0.26 or over 1.65).[1]

The model then forecasts 20-year progression:[1]

• Low risk (0 factors) — about 5 percent absolute risk at 20 years.
• Low-intermediate (1 factor) — about 20 percent.
• High-intermediate (2 factors) — about 35 to 40 percent.
• High risk (3 factors) — about 50 to 60 percent.[1]

Why the IgM clone is a little different

The same IMWG model applies to IgM MGUS, but because the isotype is automatically non-IgG, IgM MGUS sits at low-intermediate risk at minimum — and its preferred exit is Waldenstrom rather than myeloma. That is the single reason an IgM MGUS is watched a little more closely than a garden-variety IgG one.

[1]

Why IgM, not IgG, thickens the blood

The whole emergency flows from one molecule's size and one number about where it lives. IgM is a 970-kDa pentamer (an IgG monomer is 150 kDa), five units joined by a J-chain — and about 80 percent of it is trapped in the intravascular space, versus roughly half of IgG. Two consequences follow, and both are examinable.[2]

First, IgM raises serum viscosity disproportionately as its concentration climbs. Hyperviscosity complicates 10 to 30 percent of Waldenstrom macroglobulinaemia but only 2 to 6 percent of IgG myeloma, and symptoms typically appear once IgM exceeds 3 g/dL (30 g/L) — a level IgG and IgA paraproteins rarely reach, which is why hyperviscosity is overwhelmingly an IgM story.[2][12]

Second — and this is the therapeutic lever — because most of the molecule sits in the circulation, plasmapheresis removes it efficiently and turns symptoms around quickly. The molecule that causes the problem is the molecule the machine can reach.[2][12]

The molecular fork — MYD88 L265P and CXCR4

Waldenstrom wears one mutation like a name badge, and it changes both the diagnosis and the treatment. The WM clone is a post-germinal-centre B cell with plasmacytic differentiation — a lymphoplasmacytic cell that colonises marrow (paratrabecular and nodular), nodes and spleen and constitutively secretes IgM. Its immunophenotype (surface IgM+, CD19+, CD20+, CD22+, CD25+, CD27+, FMC7+, CD5-, CD10-, CD23-, CD103-, CD138-) separates it from CLL (CD5+, CD23+), mantle cell (CD5+, cyclin-D1, t(11;14)) and marginal-zone lymphoma.[3]

The molecular hallmark is MYD88 L265P, found in over 90 percent of WM — one of the highest frequencies of any recurrent point mutation in a B-cell lymphoma. MYD88 is an adaptor in the Toll/IL-1 receptor pathway; the L265P swap drives constitutive IRAK4–IRAK1–TRAF6 signalling, firing NF-kB (BCL2, BCL-XL) and interleukin-6/interleukin-10 autocrine loops. The mutation is essentially absent in IgM MGUS, which is how it separates precursor from established disease — and the chronic B-cell-receptor signalling it sustains runs straight through BTK, the target of the BTK inhibitors.[7]

The second mutation, CXCR4 (a WHIM-like truncating change), sits in roughly 30 to 40 percent of cases and often co-exists with MYD88 L265P. CXCR4 drives AKT/ERK signalling and predicts higher IgM, hyperviscosity, and a slower early response to BTK inhibitors — which still work, just more gradually. TP53 inactivation (5 to 10 percent) carries adverse outcome. The combined MYD88/CXCR4 status is both diagnostic (separating WM from marginal-zone lymphoma and IgM MGUS) and therapeutic (predicting BTK-inhibitor kinetics).[7]

The paraprotein side-shows — name them as a cluster

Examiners reward the candidate who can list what the IgM molecule does to five different organs. The same pentamer that thickens blood also precipitates in the cold, fixes complement on red cells, sticks to myelin, seeds the meninges, and folds into amyloid. Name the cluster:[1]

• Type I cryoglobulinaemia — monoclonal IgM precipitates in the cold and re-dissolves on rewarming, depositing in skin capillaries as purpura, acrocyanosis and livedo, arthralgia and weakness, and (with renal involvement) an immune-complex membranoproliferative glomerulonephritis.
• Cold agglutinin disease — monoclonal IgM with anti-I (or anti-i) specificity fixes complement (C4) in the cool periphery; the membrane-attack complex lyses red cells, giving chronic haemolytic anaemia with acrocyanosis and a direct antiglobulin test positive for C3 (anti-C3 positive, anti-IgG negative).
• Anti-MAG neuropathy — IgM binds myelin-associated glycoprotein, producing a chronic distal demyelinating sensorimotor neuropathy with sensory ataxia and postural tremor; less often the target is ganglioside (anti-GM1, anti-GD1b) or sulfatide.
• Bing-Neel syndrome — direct CNS infiltration by lymphoplasmacytic cells of brain parenchyma, meninges or cranial nerves; this is cellular, not paraprotein, because IgM does not cross the blood-brain barrier.
• AL amyloidosis — the IgM light chain (usually kappa) deposits as amyloid, causing proteinuria, nephrotic syndrome, restrictive cardiomyopathy, hepatosplenomegaly and macroglossia (less often than in IgG/IgA myeloma).[1]

The hyperviscosity triad — HYPE

Three symptoms, one bedside sign, one machine. In hyperviscosity the patient bleeds from mucosa, loses vision, and stumbles — because thick blood sludges through capillaries in the gums and gut, the retinal veins, and the cerebral microcirculation. The fundus is the single most useful bedside test in the disease: engorged tortuous 'sausage-string' retinal veins that alternate dilated and constricted segments, scattered with flame and dot-blot haemorrhages, cotton-wool spots, and papilloedema. The finding is sometimes called fundus paraproteinaemicus, and seeing it is a trigger for emergency plasma exchange — examine the fundus of any IgM-paraprotein patient with visual or neurological symptoms.[2]

[2]

The classic trap: the registrar who reaches for two units of blood before the plasmapheresis machine. Do NOT transfuse first. Red cells raise haematocrit and worsen viscosity, and a transfusion in uncontrolled hyperviscosity can precipitate stroke or acute coronary events. Plasmapheresis first, transfuse later — slowly, one unit at a time, after the viscosity has fallen.[2]

[1]

A monoclonal IgM is not, by itself, Waldenstrom

Before you commit to treatment, split two questions: is this really an IgM-clonal disease, and is the symptom really hyperviscosity? Not every IgM paraprotein is Waldenstrom, and not every hyperviscosity is IgM.[1]

[1]

And hyperviscosity is broader than Waldenstrom — the causes split into protein and cellular:[1]

• Protein causes — IgM (Waldenstrom — commonest, threshold typically over 30 to 40 g/L); IgG and IgA myeloma (only at very high levels, e.g. over 60 to 70 g/L); polyclonal hypergammaglobulinaemia (rare).
• Cellular causes — polycythaemia rubra vera (red-cell mass, haematocrit over 0.55 in men or 0.50 in women, JAK2 V617F); hyperleukocytosis in AML (WBC over 100, with leukostasis) or CML/CLL blast crisis; sickle-cell disease (rigid sickled red cells).
• The discriminator — the blood count and film separate the cellular causes; electrophoresis and immunofixation separate the protein causes. Check both in any suspected hyperviscosity.[2]

Anti-MAG neuropathy — the one electrophysiological discriminator

Anti-MAG neuropathy must be separated from CIDP (more rapid, motor-predominant, CSF pleocytosis, steroid/IVIG-responsive), diabetic length-dependent polyneuropathy, and paraneoplastic neuropathy (anti-Hu). The clue is a very slow distal motor latency (under 25 m/s, often over 1.5 times the upper limit) on nerve-conduction studies with a high-titre anti-MAG antibody.

[1]

Investigations — confirm the clone, then stage it

Send the bloods that confirm an IgM clone, the marrow that proves WM, and the viscosity that flags the emergency. First-line bloods: full blood count and film (normocytic anaemia from marrow infiltration, rouleaux as IgM stacks red cells, thrombocytopenia in advanced disease); ESR markedly elevated (often over 100 mm/h, again from rouleaux); CRP; U&E/creatinine (amyloid or cryoglobulinaemic renal disease); calcium typically normal (hypercalcaemia is uncommon in WM, unlike myeloma); albumin; LDH; beta-2 microglobulin (prognostic — see IPSS-WM); LFTs; urinalysis (proteinuria suggesting amyloid or cryoglobulinaemia); and quantitative immunoglobulins (raised IgM, suppressed IgG/IgA — immune paresis).[1][3]

The paraprotein workup is where the diagnosis lives:[1]

• Serum protein electrophoresis (SPEP) plus immunofixation — detects and types the IgM M-band; serial measurement tracks disease burden and response. Quantify IgM by nephelometry (more accurate than densitometry at high levels).
• Urine protein electrophoresis and immunofixation (Bence-Jones) — present in roughly 30 to 40 percent but rarely nephrotoxic in WM (unlike myeloma cast nephropathy).
• Serum free light chains (kappa/lambda ratio) — abnormal in roughly 30 to 40 percent of WM; part of MGUS risk-stratification.
• Serum viscosity — measured when IgM is high or symptoms suggest hyperviscosity; symptomatic hyperviscosity typically appears at a relative serum viscosity of about 4 (normal under 1.8; water = 1).[1]

Bone-marrow aspirate and trephine biopsy is the diagnostic cornerstone. Look for lymphoplasmacytic infiltration of 10 percent or more (small B-lymphocytes, plasmacytoid lymphocytes and plasma cells, often with Dutcher bodies and increased mast cells); flow cytometry shows surface IgM+, CD19+, CD20+, CD22+, CD25+, CD5-, CD10-, CD23-, CD138-. Add MYD88 L265P mutation testing (allele-specific PCR on marrow or peripheral blood, sensitivity over 95 percent) and increasingly CXCR4 testing, which predicts early BTK-inhibitor response.[3][7]

The imaging and special tests that close the loop:[1]

• Contrast-enhanced CT of neck, chest, abdomen and pelvis for lymphadenopathy and splenomegaly. A skeletal survey is NOT required (bone disease is not typical of WM; rarely osteosclerosis raises POEMS).
• Cryoglobulins — sample must be drawn, transported and processed WARM (kept at 37 degrees C from the moment of draw) to avoid in-vitro precipitation. A falsely negative cryoglobulin from a cold sample is a classic pitfall.
• Cold agglutinin titre and direct antiglobulin (Coombs) test — anti-C3 positive (anti-IgG negative) in CAD; cold agglutinin titre typically over 1:64 at 4 degrees C.
• Anti-MAG antibodies and nerve-conduction studies for neuropathy (markedly prolonged distal motor latency).
• Hepatitis B, C and HIV serology before rituximab or chemo-immunotherapy (hepatitis B reactivation risk); HCV is weakly associated with WM and mixed cryoglobulinaemia.
• Cardiac biomarkers (NT-proBNP, troponin) and echocardiogram if amyloidosis is suspected.
• Coagulation screen — IgM can interfere with fibrin polymerisation, factor VIII, von Willebrand factor and platelet function, giving a prolonged APTT or bleeding time without true factor deficiency; this usually needs no correction before procedures.[1]

IPSS-WM — the five factors that set survival

In symptomatic, treated WM, the International Prognostic Scoring System (IPSS-WM, Morel et al., Blood 2009) stratifies survival from five adverse factors. Memorise the five — they recur in every prognostic stem:[5]

[5] [5]

A revised IPSS-WM incorporating LDH and genomic risk (TP53, MYD88/CXCR4 status) has been proposed, but the five-factor model remains the standard bedside stratification.[5]

Plasmapheresis first, transfuse never — the emergency bundle

Treat the emergency before you treat the clone. Symptomatic hyperviscosity gets urgent therapeutic plasma exchange — because most IgM circulates intravascularly, exchange removes it efficiently and symptoms improve rapidly. Exchanges repeat daily or on alternate days until symptoms resolve, with definitive therapy started in parallel.[2][12]

[2] [12]

The supportive pitfalls that kill patients in hyperviscosity:[1]

• Transfuse cautiously — red-cell transfusion worsens viscosity and can precipitate or aggravate hyperviscosity, stroke or acute coronary events. Plasmapheresis first, then transfuse only as needed, slowly, after viscosity has fallen.
• Avoid dehydration — keep well hydrated with isotonic fluids; viscosity climbs when the patient runs dry.
• Avoid over-diuresis and nephrotoxins (NSAIDs, contrast); manage bleeding with local measures (nasal packing, tranexamic acid mouthwash), and only after plasmapheresis if severe.
• Avoid platelet transfusion unless profoundly thrombocytopenic — platelets add to sludging.
• Hold antiplatelet agents and anticoagulants while viscosity is high.[1]

Severe anaemia with hyperviscosity is the scenario that tempts the transfuse-first reflex. Resist it: plasmapheresis first to drop the viscosity, then cautious transfusion of one unit at a time, slowly, with monitoring. The anaemia reflects marrow infiltration and will improve once definitive therapy works.[2]

Who gets treated — and who just gets watched

WM is incurable but highly treatable, and the rule that protects patients is simple: treat symptoms, never the paraprotein number. The International Workshop for Waldenstrom Macroglobulinaemia consensus indications for treatment are:[3][4]

• Hyperviscosity syndrome — the absolute indication, even after plasmapheresis.
• Symptomatic anaemia (Hb under 10 g/dL) or symptomatic cytopenia (platelets under 100 × 10⁹/L) from marrow infiltration.
• Bulky lymphadenopathy or splenomegaly with compressive symptoms or B-symptoms.
• Symptomatic neuropathy (especially anti-MAG), cryoglobulinaemia, cold agglutinin disease, amyloidosis, or other paraprotein-mediated organ damage.
• B-symptoms — fever, night sweats, weight loss over 10 percent.
• Recurrent infection from immune paresis.[1]

Asymptomatic patients — smouldering WM and IgM MGUS — are NOT treated. They are observed, mirroring the watch-and-wait of early CLL; a high IgM alone, without symptoms, is a reason to watch more closely, not to reach for chemotherapy. MGUS is, after all, the most benign clonal diagnosis in haematology — its only real danger is being forgotten about.[1]

The treatment algorithm, first line to relapse:[1]

[1] [6] [9] [13]

Definitive therapy — rituximab-based or a BTK inhibitor

Two families dominate first line: fixed-duration rituximab chemoimmunotherapy, and continuous oral BTK inhibition. Choose by age, fitness, cytopenias, IgM burden, MYD88/CXCR4 status, and how fast you need the IgM to fall.[3][4][6]

[9] [13] [8]

BTK inhibitors (continuous, oral, fixed-dose) target the B-cell-receptor signalling the MYD88-driven clone depends on, and are active in both untreated and relapsed WM:[1]

[4] [14] [4] [10] [3]

The classic trap — the rituximab IgM flare. Rituximab can trigger a transient IgM rise in the weeks after the first dose, occasionally tipping the patient into hyperviscosity — in the INNOVATE trial, flares occurred in 47 percent of patients receiving rituximab alone versus 8 percent receiving ibrutinib plus rituximab. In anyone with very high IgM, delay rituximab (use a BTK inhibitor or bortezomib first, or plasmapheresise) and monitor closely. Bortezomib and BTK inhibitors do not flare, which is why they are preferred for rapid IgM control.[6][11]

Other agents and emerging options:[1]

• Venetoclax (BCL-2 inhibitor) — oral, active in WM (over 80 percent ORR); watch for tumour-lysis syndrome with gradual ramp-up; useful in relapsed disease.
• Carfilzomib and daratumumab — second-line proteasome-inhibitor and anti-CD38 options; daratumumab interferes with blood-typing (CD38 on red cells needs dithiothreitol treatment before typing).
• Chlorambucil — older oral alkylator, affordable in low-resource settings but less effective and leukaemogenic with prolonged use.
• Autologous stem-cell transplant — reserved for younger, fit patients with chemosensitive relapsed disease; not first-line.[1]

MGUS itself is never treated — arrange lifelong monitoring (SPEP and free-light chains, 6-monthly for the first year then annually if stable), risk-stratify by the IMWG model, and teach the red flags: rising M-protein, new anaemia, bone pain, or any hyperviscosity symptom.[1]

Type I cryoglobulinaemia or cold agglutinin disease complicating WM are managed by treating the underlying clone (rituximab-based); supportive measures are cold avoidance, and for severe CAD sutimlimab (anti-C1s), which raises haemoglobin by blocking the classical complement pathway.[1]

The trials that set the regimen

[4] [6] [7]

The takeaway from the evidence base: zanubrutinib is the preferred BTK inhibitor after ASPEN (less atrial fibrillation, hypertension and bleeding than ibrutinib), and ibrutinib plus rituximab is an evidence-based first-line option after INNOVATE — the basis of the MYD88-driven clone's BTK dependence.[4][6][7]

The subtypes and scenarios that bite

• Smouldering (asymptomatic) Waldenstrom — observe as for smouldering myeloma; treat only when symptomatic. Hyperviscosity, anaemia, neuropathy or bulky disease are the usual triggers. Patients with very high IgM (over 60 g/L) are at higher risk of imminent hyperviscosity and may warrant earlier therapy.
• Bing-Neel syndrome (CNS WM) — direct infiltration of brain parenchyma, meninges or CSF; presents with headache, cranial neuropathy, seizures or focal deficit. Manage with CNS-penetrant therapy: high-dose methotrexate or cytarabine, ibrutinib or zanubrutinib (which cross the blood-brain barrier and are active in Bing-Neel), and/or intrathecal therapy, plus systemic control. MRI brain and CSF flow cytometry are diagnostic.[3]
• WM-associated anti-MAG neuropathy — slowly progressive distal demyelinating neuropathy; responds variably to rituximab (often single-agent, sometimes with bendamustine). Improvement is delayed (6 to 12 months) and incomplete.
• Type I cryoglobulinaemia — cold-precipitating monoclonal IgM; treat the underlying WM. Severe skin ulceration or renal involvement warrants urgent plasmapheresis followed by rituximab-based therapy.
• Cold agglutinin disease (CAD) — IgM-mediated complement haemolytic anaemia; treat the underlying WM with rituximab-based therapy; sutimlimab (anti-C1s) is approved for refractory CAD and rapidly raises haemoglobin. Supportive: folic acid, transfusion via blood-warmer, cold avoidance.
• AL amyloidosis complicating WM — treat the underlying clone (often BR); cardiac and renal supportive care as for any AL amyloidosis.[3]

The classic traps — the recurring exam errors

Name these out loud in the viva — each one is a stem in disguise:[1]

• Attributing anaemia, neuropathy or fatigue to "old age" and missing an IgM paraprotein — measure SPEP and IgM in any older adult with unexplained normocytic anaemia, raised ESR, chronic neuropathy, nephrotic-range proteinuria or chronic haemolysis.
• Transfusing before plasmapheresis in hyperviscosity — worsens viscosity and can precipitate stroke. Plasmapheresis first.
• Drawing the cryoglobulin sample cold — it precipitates in vitro; transport warm at 37 degrees C from draw to laboratory.
• Forgetting MYD88 L265P testing when marrow morphology is ambiguous (separates WM from marginal-zone lymphoma and IgM MGUS).
• Confusing MGUS with myeloma — MGUS has no CRAB, paraprotein under 30 g/L, and marrow under 10 percent; treat by monitoring, not chemotherapy.
• Using rituximab monotherapy in very high IgM — risks the IgM flare and hyperviscosity. Delay rituximab or plasmapheresise first.
• Misattributing a prolonged APTT to a true bleeding disorder when it is the IgM interfering with the assay in vitro.[1]

Prognosis, and the score that sets it

WM remains incurable but treatable, with median overall survival of about 5 to 10 years — and improving with BTK inhibitors and modern chemoimmunotherapy. Outcome is set by the IPSS-WM (age, haemoglobin, platelets, beta-2 microglobulin, IgM) plus adverse modifiers: high LDH, refractory disease, 6q deletion, TP53 mutation, and transformation to DLBCL.[3][4][5]

[5]

MGUS carries its constant about 1 percent per year progression risk — the patient is never truly discharged. Arrange lifelong monitoring of the M-protein and free-light chains. Histological transformation to DLBCL (a Richter-like event, about 5 percent of patients) heralds aggressive disease with median survival under 2 years and needs R-CHOP plus or minus autologous SCT in selected patients.[1]

Follow-up is by serial IgM M-protein monitoring (IWWM-6 response criteria), surveillance for treatment toxicity (FBC, LFTs, immunoglobulins, infection prophylaxis), and assessment for progression or transformation (rising IgM, new B-symptoms, rising LDH, new tissue masses).[1]

Special populations — thresholds and choices shift

• Elderly and frail — prefer lower-toxicity regimens (DRC, single-agent BTK inhibitor); a BTK inhibitor is oral and avoids chemotherapy myelosuppression. Select therapy by physiological, not chronological, age.
• Pregnancy — WM and symptomatic MGUS are rare; observe where possible. If hyperviscosity develops, plasmapheresis (safe in pregnancy) is the emergency measure. Avoid teratogenic chemotherapy (bendamustine, cyclophosphamide) and BTK inhibitors. Rituximab is avoided near term (neonatal B-cell depletion for 6 months).
• Renal impairment or CKD — avoid nephrotoxic regimens; bendamustine and rituximab are usable with dose adjustment; manage cryoglobulinaemic glomerulonephritis by treating the underlying disease (plasmapheresis for severe cases).
• Hepatic impairment — bendamustine and bortezomib are hepatically metabolised; dose-adjust in severe impairment.
• Pre-existing peripheral neuropathy — avoid bortezomib; the underlying anti-MAG neuropathy may improve with WM treatment.
• Prior hepatitis B — antiviral prophylaxis (entecavir or tenofovir) before rituximab or a BTK inhibitor, regardless of viral load.
• Cardiovascular disease — prefer zanubrutinib over ibrutinib if atrial fibrillation or hypertension is present (ASPEN trial); BTK inhibitors interact with CYP3A4 substrates (statins, anticoagulants).
• Community monitoring of IgM MGUS — 6-monthly SPEP and free-light chains for the first year, then annually if stable; teach the red flags.[1]

Guidelines and regional deltas

The International Workshop for Waldenstrom Macroglobulinaemia (IWWM) consensus (now in its 11th iteration) defines diagnostic criteria and treatment indications: treat symptomatic disease; prefer rituximab-based chemoimmunotherapy or a BTK inhibitor first-line. NCCN (US) and ESMO (Europe) are largely concordant, with regional access driving practical variation.[3]

[1] [1] [1]

Controversies to name calmly:[1]

• When to treat asymptomatic disease — consensus is watch-and-wait even with high IgM, though newer data suggest earlier BTK-inhibitor therapy may improve quality of life in some high-burden smouldering WM.
• Fixed-duration chemoimmunotherapy versus continuous BTK inhibitor — both are first-line; choice turns on patient preference, fitness, need for a treatment-free interval, and access.
• Role of venetoclax — high response rates but tumour-lysis concern and the need for ramp-up; useful in relapsed disease.
• MYD88/CXCR4-guided therapy — CXCR4-mutated disease responds more slowly to BTK inhibitors but does eventually respond; future trials may select therapy by genotype.[1]

The high-yield core

[1]

• MGUS criteria: under 30 g/L, under 10 percent, no CRAB. Non-IgM MGUS progresses at 1 percent per year; IgM MGUS at roughly 1.5 to 2 percent per year (often to Waldenstrom).
• MYD88 L265P in over 90 percent of WM — diagnostic and the basis of BTK-inhibitor dependence; CXCR4 mutation in 30 to 40 percent (slower early BTK response, higher IgM).
• Why IgM causes hyperviscosity but IgG rarely does: IgM is a 970-kDa pentamer and 80 percent intravascular; IgG is a 150-kDa monomer, about half extravascular. Plasmapheresis removes IgM efficiently.
• Symptomatic threshold: serum relative viscosity about 4 (water = 1; normal under 1.8); symptoms common when IgM is over 40 g/L.
• Rituximab IgM flare: in very high IgM (over 40 g/L) delay rituximab or plasmapheresise first; use bortezomib or a BTK inhibitor for rapid control.
• Hyperviscosity is broader than Waldenstrom — polycythaemia rubra vera, hyperleukocytosis (AML/CML), IgG/IgA myeloma (very high), sickle cell.
• BR dose: bendamustine 90 mg/m² days 1 and 2, rituximab 375 mg/m² day 1, every 28 days, 4 to 6 cycles.
• DRC dose: dexamethasone 20 mg, rituximab 375 mg/m², cyclophosphamide 100 mg/m² days 1 to 5, every 21 days, 6 cycles.
• BTK inhibitors: zanubrutinib 160 mg BD (preferred — ASPEN trial), ibrutinib 420 mg OD.
• Plasmapheresis: 1 to 1.5 plasma volumes daily, removes 30 to 60 percent IgM per session.
• IPSS-WM: age over 65, Hb at or below 11.5 g/dL, platelets at or below 100, beta-2 microglobulin over 3, IgM over 7 g/L — low / intermediate / high risk with median survival ~12 / ~8 / ~3.5 years.
• Bing-Neel syndrome = CNS infiltration by WM cells (not paraprotein, because IgM does not cross the BBB).
• Cold agglutinin in WM: anti-C3 positive direct antiglobulin test; sutimlimab (anti-C1s) for refractory CAD.[1]

The mantra

The mantra: Plasmapheresis first, transfuse never — then go after the clone.[1][2]

Etymology for viva gold: Jan Waldenstrom, the Swedish physician who described the macroglobulinaemia syndrome in 1944, never saw MYD88 — but the pentamer he spotted in the ultracentrifuge is exactly the molecule the apheresis machine now pulls out. Forgotten name, not gone problem.[3]

Ward-round test — three stems, thirty seconds each

Stem 1 — the man from the top of the topic (answer)

A 68-year-old man with epistaxis, blurred vision and ataxia. The registrar wants a CT head and two units of blood. What is the next best step? Model: This is the hyperviscosity triad in an IgM-paraprotein patient — hyperviscosity until proven otherwise. The next best step is fundoscopy (look for sausage-string retinal veins), send SPEP/immunofixation and serum viscosity, and arrange urgent plasmapheresis — not a CT head, and not a transfusion. Do not transfuse first: red cells raise haematocrit and worsen viscosity, and can precipitate stroke. After the emergency, treat the underlying WM with rituximab-based therapy (delaying rituximab when the IgM is very high to avoid the IgM flare) or a BTK inhibitor.

[1] [2] [6]

Stem 2 — very high IgM before rituximab (answer)

A 72-year-old with newly diagnosed WM has an IgM of 55 g/L but no hyperviscosity symptoms yet. The team plans bendamustine-rituximab. What must you do first? Model: With a very high IgM, rituximab risks the IgM flare — a transient IgM rise in the weeks after the first dose that can tip the patient into hyperviscosity (flares occurred in 47 percent of patients on rituximab alone in the INNOVATE trial, versus 8 percent with ibrutinib plus rituximab). Either delay rituximab — use bortezomib for rapid IgM reduction, or a BTK inhibitor — or plasmapheresise first with close monitoring. Bortezomib and BTK inhibitors do not flare, which is why they are preferred for rapid IgM control.

[2] [6]

Stem 3 — the MGUS that changed (answer)

A 64-year-old with known IgM MGUS (M-protein stable at 12 g/L for 5 years) presents with new fatigue, Hb 92 g/L, and back pain. What has happened, and what do you do? Model: This is progression — rising disease burden with new anaemia. Reassess urgently: repeat SPEP and IgM, FBC and film, calcium and renal function (CRAB), and arrange bone-marrow biopsy with MYD88 L265P testing and CT staging. The differential is progression to Waldenstrom (most likely, given IgM isotype) versus a separate myeloma or lymphoma. Do not continue routine MGUS monitoring — this patient has crossed a line and now needs staging and treatment indications assessed.

[1]

References

1. [1]Gonsalves WI, Rajkumar SV. Monoclonal Gammopathy of Undetermined Significance Ann Intern Med, 2022.PMID 36508741
2. [2]Gertz MA. Acute hyperviscosity: syndromes and management Blood, 2018.PMID 30104220
3. [3]Ghafoor B, Masthan SS, Hameed M, et al. Waldenström macroglobulinemia: a review of pathogenesis, current treatment, and future prospects Ann Hematol, 2024.PMID 37414960
4. [4]Tam CS, Opat S, D'Sa S, et al. A randomized phase 3 trial of zanubrutinib vs ibrutinib in symptomatic Waldenström macroglobulinemia: the ASPEN study Blood, 2020.PMID 32731259
5. [5]Morel P, Duhamel A, Gobbi P, et al. International prognostic scoring system for Waldenstrom macroglobulinemia Blood, 2009.PMID 19196866
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