Antiphospholipid Syndrome — SCE Dermatology MCQ

Correct answer: C — Small vessel thrombosis from antiphospholipid syndrome

The correct answer is C, small vessel thrombosis from antiphospholipid syndrome. Antiphospholipid syndrome (APS) is characterised by thrombosis, including microvascular thrombosis, occurring in the presence of persistently positive antiphospholipid antibodies such as lupus anticoagulant and anti-cardiolipin antibody. In this patient, painful fingertip vasculopathy progressing to digital gangrene, combined with a positive lupus anticoagulant and anti-cardiolipin antibody, is the classic pattern of APS-driven occlusive small vessel thrombosis rather than an inflammatory vasculitic or purely vasospastic process. The mechanism involves antiphospholipid antibody binding to phospholipid-protein complexes on endothelium and platelets, triggering endothelial activation, platelet aggregation and a hypercoagulable state that occludes digital arterioles and capillaries, producing ischaemic gangrene. This occurs as secondary APS in the context of her long-standing SLE. Why the other options are wrong: E. Cryoglobulinaemia: this causes small vessel occlusion via cryoglobulin precipitation in the cold, typically with purpura and positive cryoglobulins or hepatitis C association, not lupus anticoagulant or anti-cardiolipin positivity. A. Raynaud phenomenon alone: Raynaud causes reversible vasospasm with pallor, cyanosis and rewarming, but does not by itself cause fixed thrombosis or gangrene; the positive antiphospholipid antibodies point to a thrombotic rather than purely vasospastic cause. D. Atherosclerosis: this affects larger arteries in older patients with vascular risk factors, producing gradual ischaemia, not acute digital gangrene with positive lupus anticoagulant in a 48-year-old woman. B. Large vessel vasculitis: conditions such as Takayasu arteritis affect large arteries with claudication and pulse asymmetry, not digital microvascular occlusion, and are not defined by antiphospholipid antibodies. Key point: digital gangrene with positive lupus anticoagulant and anti-cardiolipin antibodies in SLE indicates small vessel thrombosis from antiphospholipid syndrome, requiring anticoagulation rather than immunosuppression alone.

Reference: British Society for Haematology (BSH), Guidelines on the investigation and management of antiphospholipid syndrome, 2024, https://onlinelibrary.wiley.com/doi/10.1111/bjh.19635