Which condition presents with painful, purple skin lesions within the first days to weeks after starting warfarin therapy?

• A. Erythema nodosum
• B. Coumadin skin necrosis
• C. Diabetic dermopathy
• D. Livedo reticularis

Answer: (B)

Warfarin-induced skin necrosis occurs when starting warfarin leads to a rapid drop in protein C (which has a short half-life), creating a temporary hypercoagulable state. This promotes microvascular thrombosis in the skin, especially in areas with more subcutaneous fat, causing painful, purplish lesions that can progress to necrosis within days to weeks of initiating therapy. It’s a recognizable adverse effect of initiating warfarin, particularly in patients with or without underlying deficiencies of natural anticoagulants.

This pattern is distinct from erythema nodosum, which are tender nodules from inflammatory processes and not linked to starting anticoagulation; from diabetic dermopathy, which presents as painless shin spots due to microangiopathy; and from livedo reticularis, which is a net-like vascular pattern that isn’t characteristically necrotic and tied to warfarin initiation.