An atypical presentation of catastrophic antiphospholipid syndrome with refractoriness to treatment.

Catastrophic antiphospholipid syndrome (CAPS) is a rare and life-threatening manifestation of antiphospholipid syndrome (APS). Diagnosing CAPS can be particularly challenging, especially due to significant overlap in pathophysiology, signs, and symptoms with other complex hematologic conditions, including thrombotic microangiopathies (TMA) and immune-mediated thrombocytopenia (ITP). In many cases, definitive diagnosis is not clear, leading to delays in care and poor outcomes. Here, we present an elderly patient with previously diagnosed APS now presenting with suspected CAPS, admitted to our inpatient service with a complicated hospital course. The patient received daily plasma exchange, steroids, intravenous immunoglobulin, and therapeutic heparin for anticoagulation. Despite treatment, there was worsening of thrombocytopenia suggesting refractoriness to ongoing treatment. We outline our diagnostic approach, clinical evaluation, treatment strategies, and differential diagnoses pertinent to our atypical clinical presentation of CAPS.