Cold Agglutinin Disease: Fast and Indefinite, or Slower With a Possible Exit
A single patient, whose hemolysis is reliably tied to a hobby he won't give up. The disagreement isn't whether he needs therapy before winter — it's whether speed or an eventual exit matters more.
Harold B. has spent nearly every winter Saturday for the past six years ice fishing on the same lake his father took him to as a boy, a ritual he picked back up once he retired from the county library system — a hobby his hematologist has learned to ask about directly, since it is also reliably when his symptoms are worst. He has cold agglutinin disease, confirmed by a high-titer IgM cold agglutinin with classic anti-I specificity and a bone marrow biopsy showing a clonal lymphoproliferative population too small to meet criteria for overt lymphoma, the typical underlying substrate in cold agglutinin disease even when no separate malignancy diagnosis is ever made.
Every winter for the past two years he has needed at least one transfusion after a hemolytic flare triggered by exactly the kind of prolonged cold exposure his hobby guarantees, with his hemoglobin dropping into the low 6s on the worst of those occasions, accompanied by the dark urine and acrocyanosis in his fingertips that mark an acute flare. He has tried strict cold avoidance, which is not realistic advice for a man who has built his retirement around a lake in January, and his hemoglobin runs chronically in the 9s even between flares.
The two real first-line options work through genuinely different mechanisms with different practical costs. Sutimlimab, a complement C1s inhibitor, produced rapid hemoglobin responses in CARDINAL and CADENZA, both enrolling patients with a transfusion history much like his own, but requires indefinite biweekly infusions with no natural stopping point. Rituximab-based therapy works more slowly and less reliably in cold agglutinin disease specifically than in warm AIHA, since the underlying clonal B-cell population it targets tends to be smaller and less actively proliferating here, but carries a real chance of a treatment-free remission that would let him manage his winters without becoming a lifelong infusion patient.
Fast and indefinite, or slower with a possible exit
Given that his flares are predictably tied to a specific, recurring winter exposure he isn't going to give up, I'd start sutimlimab now, timed to be fully active before the season starts. CARDINAL and CADENZA both showed rapid, reliable hemoglobin response by inhibiting C1s directly — a mechanism that doesn't depend on the slower B-cell depletion rituximab requires to take effect.
The honest cost is that sutimlimab has no built-in stopping point — it isn't a course of therapy, it's an indefinite biweekly infusion commitment, which is worth naming to him directly rather than treating as incidental.
That indefinite-commitment point is exactly why I'd offer rituximab-based therapy as the first real option, not sutimlimab. Its response in cold agglutinin disease is genuinely less reliable and slower than in warm AIHA, so I'm not overselling it — but a real chance at treatment-free remission is worth more to a 71-year-old who wants his winters back, not a lifelong infusion schedule, than a faster response with no exit.
If his flares are severe enough that even one bad winter before rituximab has time to work is unacceptable, that argument favors sutimlimab regardless of the exit-strategy point — the severity of his prior flares is what should actually decide this, not a general preference for reversibility.
Agreed, given his two prior winters both required transfusion, that the severity argument favored starting sutimlimab now, timed ahead of the season, rather than betting the winter on rituximab's slower onset.
Not agreed: whether to revisit rituximab as a longer-term strategy after one or two stable winters on sutimlimab, to test whether a treatment-free remission becomes realistic once his disease is better controlled — left open rather than decided now.