Cold agglutinin disease
Description
- Complement-mediated haemolytic anaemia driven by a monoclonal IgM cold agglutinin
- Two clinical problems, and they need different treatment
1. Haemolysis - anaemia, jaundice, fatigue, dark urine in crises
2. Circulatory/agglutination symptoms in the cold - acrocyanosis, Raynaud-like changes, livedo reticularis, cold-induced pain, rarely acral ulceration
| Primary cold agglutinin DISEASE | Secondary cold agglutinin SYNDROME | |
|---|---|---|
| Driver | Clonal bone marrow lymphoproliferative disorder (low-grade, IgM kappa) | **Mycoplasma pneumoniae (anti-I), EBV (anti-i)**, other infection, Waldenstrom/B-cell lymphoma |
| Course | Chronic, indolent, does not remit | Transient, post-infectious - resolves in weeks |
| Treatment | B-cell directed / complement inhibition | Supportive; treat the infection |
- *Not a subtype of warm AIHA managed the same way. Steroids and splenectomy do not work.*
Epidemiology
- Rare: incidence ~1 per million/yr, prevalence ~15-20 per million
- Median age ~65-75; F>M
- More common in cold climates (Scandinavian data dominate the literature)
- ~15-25% of all autoimmune haemolytic anaemia
- Secondary (post-Mycoplasma, post-EBV) is commoner in children and young adults
Aetiopathogenesis
The antibody
- Monoclonal IgM, usually kappa, specific for the I antigen on adult red cells
- Anti-i (fetal/neonatal antigen) in EBV-associated disease
- Pentameric IgM -> highly efficient complement activation
The thermal cycle - the key to everything
- In the acral circulation (~28-31 C): IgM binds red cells and agglutinates them
- -> C1 activation -> C3b deposition
- -> agglutination causes the acrocyanosis, Raynaud-like symptoms and livedo
- On return to the core (37 C): IgM dissociates but C3b stays bound
- -> C3b-coated cells cleared by Kupffer cells in the liver (extravascular)
- -> a fraction proceed to C5b-9 MAC -> intravascular haemolysis (haemoglobinuria in crises)
- *This explains: the C3d-only DAT, why the liver rather than the spleen is the site of clearance, why splenectomy fails, and why C1s inhibition works*
Thermal amplitude vs titre
- Thermal amplitude - the highest temperature at which the antibody still binds - predicts clinical severity
- Titre does not - a high-titre antibody with a low thermal amplitude may be clinically silent
The clone
- Primary CAD is a distinct, low-grade clonal lymphoproliferative bone marrow disorder - not simply Waldenstrom
- KMT2D and CARD11 mutations; MYD88 L265P usually ABSENT (unlike Waldenstrom)
- Small clone, low tumour burden - the disease is caused by the protein, not by mass
Diagnosis
Diagnostic requirements
1. Chronic haemolysis - anaemia, high LDH, high unconjugated bilirubin, low haptoglobin, reticulocytosis
2. *DAT positive for C3d and negative (or only weakly positive) for IgG*
3. Cold agglutinin titre >=1:64 at 4 C
4. No overt lymphoma on imaging or marrow (a small clonal population on flow or trephine is expected and does not exclude primary CAD)
Laboratory traps - these are the examinable points
- *Spuriously high MCV and spuriously low red cell count and haematocrit* - agglutinated cells counted as single large cells
- Fix: warm the sample to 37 C and re-run
- Red cell agglutination on the film - clumps, not rouleaux; disperses on warming (rouleaux does not)
- ABO grouping and crossmatching fail - autoagglutination; the sample must be warmed and prewarmed techniques used
- Sample must be transported at 37 C for cold agglutinin titre
Workup for a driver
- Serum EPG/immunofixation and free light chains - an IgM kappa paraprotein is usual
- Peripheral blood flow cytometry, CT chest/abdo/pelvis, bone marrow aspirate and trephine - characterise the clone, exclude overt lymphoma
- **Mycoplasma and EBV serology** if acute or in a younger patient
- Consider hepatitis C, HIV
Distinguish from
| Discriminator | |
|---|---|
| Warm AIHA | DAT IgG positive, spherocytes, responds to steroid, splenomegaly |
| Paroxysmal cold haemoglobinuria | Donath-Landsteiner biphasic IgG anti-P; children, post-viral, intravascular |
| Cryoglobulinaemia | Vasculitic purpura, arthralgia, neuropathy, low C4; cryocrit rather than agglutinins |
| Raynaud phenomenon | Triphasic colour change, no haemolysis |
| PNH | Flow cytometry for GPI-anchored protein loss; DAT negative |
Management
A. Cold avoidance - the foundation, and often sufficient in mild disease
- Warm clothing incl. gloves, hat and warm footwear; heated home and car; avoid cold environments and cold drinks
- *All IV fluids and blood products through a blood warmer*
- Warm the operating theatre; avoid hypothermic cardiopulmonary bypass - cardiac surgery in CAD requires normothermic or warm-cardioplegia protocols, planned in advance
- Treat any intercurrent infection promptly - complement amplification causes exacerbations
B. When to treat
- Symptomatic anaemia, transfusion dependence, disabling circulatory symptoms, or acral ulceration
- Asymptomatic mild anaemia: cold avoidance and observation
C. What does NOT work
- *Corticosteroids* - responses are infrequent, incomplete and require unacceptable maintenance doses
- *Splenectomy* - clearance is hepatic, not splenic
- Both are frequently and incorrectly tried first
D. B-cell directed therapy - treat the clone
- Rituximab monotherapy - response ~45-60%, median duration ~1 year
- Rituximab + bendamustine - response ~70-80% with much longer duration; the preferred option in fit patients
- Rituximab-fludarabine (more toxic); bortezomib-based regimens; ibrutinib in selected cases
E. Complement inhibition
- Sutimlimab - humanised anti-C1s monoclonal, blocks the classical pathway
- Rapid: haemoglobin rises and transfusion requirement falls within weeks (CARDINAL, CADENZA)
- Abolishes haemolysis but NOT the agglutination-mediated circulatory symptoms - the IgM still binds; only complement is blocked
- *Indefinite therapy required - haemolysis returns on cessation*
- Meningococcal (ACWY and B), pneumococcal and Hib vaccination before starting, plus antibiotic prophylaxis
- Use where a rapid response is needed, or as a bridge while rituximab-based therapy takes effect
F. Supportive
- Folic acid 5 mg daily
- Transfusion when needed - warmed, and do not withhold it; ABO/RhD compatible, prewarmed crossmatch techniques
- Thromboprophylaxis during haemolytic exacerbations - VTE risk is increased
- Erythropoietin has been used adjunctively
- Plasma exchange gives transient benefit only (IgM is largely intravascular) - a bridge in a crisis
Associations
- Clonal bone marrow lymphoproliferative disorder (primary CAD)
- Waldenstrom macroglobulinaemia, marginal zone lymphoma, other low-grade B-cell lymphoma
- **Mycoplasma pneumoniae (anti-I) and EBV/infectious mononucleosis (anti-i)**
- Other infections - CMV, VZV, HIV, hepatitis C, Legionella
- Raynaud phenomenon, livedo reticularis, acrocyanosis
- Venous thromboembolism (increased risk during haemolysis)
- Cardiac surgery with hypothermic bypass - a recognised precipitant of catastrophic intraoperative agglutination
- Monoclonal gammopathy of clinical significance (MGCS) - CAD is a paradigm example
Natural history & complications
- Chronic and lifelong in primary disease - spontaneous remission is rare
- *Secondary (post-Mycoplasma/EBV) resolves within weeks*
- Median survival in primary CAD is close to that of the age-matched population, but quality of life is substantially impaired - fatigue, cold intolerance, transfusion dependence
- Median Hb ~90 g/L; about half require transfusion at some point
What drives exacerbations
- Cold exposure; and any febrile illness or surgery (acute-phase C3 rise amplifies complement-mediated haemolysis - patients often become more anaemic when they get an infection, not less)
Complications
- Symptomatic anaemia and transfusion dependence; iron overload with chronic transfusion
- Acrocyanosis, digital ulceration and rarely gangrene
- Venous and arterial thromboembolism
- Haemolytic crisis with haemoglobinuria and AKI
- Transformation to overt B-cell lymphoma in a minority - monitor the paraprotein and clinical features
- Complications of therapy - infection with rituximab and sutimlimab, meningococcal disease with complement blockade
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