A 58-year-old woman started on warfarin for atrial fibrillation returns on day 5 with a painful, well-demarcated necrotic skin lesion over the breast. Biopsy shows microvascular thrombosis. Which underlying abnormality predisposes to this complication?

• A Antithrombin III deficiency
• B Plasminogen activator inhibitor-1 excess
• C Dysfibrinogenemia
• D Protein C deficiency or functional protein C resistance ✓

Explanation

Warfarin-induced skin necrosis occurs because protein C, a vitamin K dependent anticoagulant with a short half-life, falls before factors II and X. In patients with pre-existing protein C deficiency, a transient hypercoagulable state results and dermal microvessels thrombose, typically over adipose-rich sites such as breast, buttock, and thigh. Management is stopping warfarin, giving vitamin K, and starting heparin or a direct oral anticoagulant. Antithrombin deficiency causes heparin resistance, not coumarin necrosis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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