A 55-year-old man started on warfarin for deep vein thrombosis returns on day 4 with painful, black, necrotic skin lesions over his thigh and breast. Biopsy shows microvascular thrombosis without vasculitis. The most likely mechanism is:

• A Type IV hypersensitivity reaction to warfarin metabolites
• B Immune complex deposition triggering leukocytoclastic vasculitis
• C Direct toxic effect of warfarin on dermal capillary endothelium
• D Transient hypercoagulability from rapid fall of protein C before factors II, IX and X decline ✓

Explanation

Protein C has the shortest half-life (about 6 hours) among the vitamin K dependent proteins, so its anticoagulant activity falls within 1 to 2 days while procoagulant factors II, IX and X persist. This transient prothrombotic state causes microvascular thrombosis in subcutaneous fat, producing warfarin-induced skin necrosis. Management is stopping warfarin, giving vitamin K and heparin, and considering protein C concentrate.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.