Catastrophic antiphospholipid syndrome: how to diagnose a rare but highly fatal disease

Antiphospholipid syndrome (APS) is a multisystem autoimmune condition characterized by vascular thromboses and/or pregnancy loss associated with persistently positive antiphospholipid antibodies (aPL). Catastrophic APS (CAPS) is the most severe form of APS with multiple organ involvement developing over a short period of time, usually associated with microthrombosis. 'Definite' and 'probable' CAPS have been defined based on the preliminary classification criteria; however, in a real-world setting, aPL-positive patients with multiple organ thromboses and/or thrombotic microangiopathies exist who do not fulfill these criteria. Previous APS diagnosis and/or persistent clinically significant aPL positivity is of great importance for the CAPS diagnosis; however, almost half of the patients who develop CAPS do not have a history of aPL positivity. The purpose of this paper is to summarize the diagnostic challenges and the recently updated diagnostic algorithms for CAPS providing a 'step-by-step' approach for clinicians (and researchers) in the assessment of patients with multiple organ thromboses.