Dermal vasculitis due to coumadin hypersensitivity.

A 65-year-old patient developed nonpruritic purpuric skin eruptions following 10 days of coumadin treatment. Skin biopsy revealed vasculitis and immunofluorescent studies demonstrated the presence of IgM and C3 deposits in the walls of the affected blood vessels. Rechallenge with coumadin was followed by reappearance of the skin eruptions. Indirect mast cell degranulation test and migration inhibiting factor test were positive in the presence of coumadin. These findings strongly suggest that the skin lesions were induced by an immunologic reaction to warfarin.