A Diagnostic Dilemma: Catastrophic or Seronegative Antiphospholipid Syndrome.

Catastrophic antiphospholipid syndrome (CAPS) and seronegative APS (SN-APS) are rare and severe variants of antiphospholipid syndrome (APS). Due to the significant morbidity and mortality associated with these variants, early recognition and adequate treatment with immunomodulatory agents and anticoagulation are crucial. Here, we report a rare presentation of seronegative CAPS in a young adult with systemic lupus erythematosus (SLE) who presented with seizures, encephalopathy, and quadriplegia. Brain imaging revealed intracranial hemorrhage and attenuated vessels in the Circle of Willis suggestive of vasculitis. Imaging also revealed bilateral pulmonary emboli involving the main pulmonary, segmental, and subsegmental arteries; lower extremity deep vein thrombosis in the right common femoral vein; and superficial venous thrombi in the left cephalic and basilic veins. Due to the absence of APS seropositivity and the catastrophic nature of her presentation, namely the widespread thrombi formation and multiorgan involvement, there was high suspicion for a diagnosis of seronegative CAPS. After two weeks of high doses of immunomodulatory agents, plasmapheresis, and intravenous immune globulin (IVIG) treatment, the patient showed clinical improvement and a reduced burden of venous thrombi. The predicament of not being able to use anticoagulation in this patient due to cerebral hemorrhage added to the complexity and uniqueness of this case.