Warfarin Skin Necrosis — SCE Dermatology MCQ

Correct answer: D — Warfarin-induced skin necrosis

A) Warfarin-induced skin necrosis is correct. The clinical picture of painful retiform purpura evolving into central necrosis on fatty sites such as thighs and buttocks, occurring in a patient recently started on or established on Warfarin, together with biopsy showing dermal and subcutaneous vessel thrombosis without vasculitis, is the classic presentation. The mechanism is a paradoxical hypercoagulable state: protein C (and protein S) have a short half-life so fall before the procoagulant factors II and X, producing transient microvascular thrombosis, especially in patients with underlying protein C or S deficiency. This typically occurs in the first days of therapy and the absence of vasculitis on histology excludes an inflammatory vasculitic process, confirming a purely thrombotic mechanism. Why the other options are wrong: B. Cryoglobulinaemia: causes palpable purpura and vasculitis on biopsy (leucocytoclastic vasculitis with vessel wall inflammation), not pure thrombosis without vasculitis, and is unrelated to Warfarin exposure. E. Calciphylaxis: occurs almost exclusively in patients with end-stage renal disease and hyperparathyroidism, with biopsy showing vascular calcification and intimal hyperplasia rather than isolated thrombosis, and is not linked to Warfarin initiation. A. Disseminated intravascular coagulation: causes widespread purpura with consumptive coagulopathy, low platelets and prolonged clotting times in the context of severe illness (sepsis, trauma), not a localised reaction to Warfarin with normal-range coagulation parameters otherwise. C. Cholesterol crystal embolisation: follows vascular intervention or catheterisation, and biopsy characteristically shows needle-shaped cholesterol clefts within vessel lumina, not simple thrombosis without vasculitis. Key point: Retiform purpura and necrosis on fatty areas within days of starting Warfarin, with biopsy showing thrombosis and no vasculitis, points to Warfarin-induced skin necrosis from protein C/S depletion outpacing procoagulant factor decline.

Reference: DermNet NZ, Warfarin induced skin necrosis, https://dermnetnz.org/topics/warfarin-induced-skin-necrosis