Azathioprine-induced bullous Sweet's syndrome: a rare association.

A 52-year-old man presented with high-grade fever, headache and painful vesicular skin rash involving the upper trunk and upper extremities, 8 days after initiation of chemotherapy with azathioprine (50 mg/day), which had been prescribed for acral vitiligo. There was neither any history of preceding respiratory or gastrointestinal tract infection, nor was the patient known to have malignancy, drug hypersensitivity, inflammatory bowel disease, vasculitis or other autoimmune disease. Laboratory results revealed leucocytosis with neutrophilia and markedly elevated acute phase reactants. Antinuclear antibody, perinuclear and cytoplasmic antineutrophil cytoplasmic antibody were found negative. Punch biopsy from skin of the upper trunk revealed dense neutrophilic infiltration of dermis without signs of vasculitis, suggestive of Sweet's syndrome. In view of the temporal association with azathioprine and absence of an obvious alternative aetiology, provisional diagnosis of drug-induced bullous Sweet's syndrome was made. Azathioprine was discontinued and high-dose oral prednisolone initiated. The response was dramatic with resolution of skin lesions within 72 h without further recurrence at fourth week of follow-up.