Erythema Nodosum as Azathioprine Hypersensitivity Reaction in a Patient with Bullous Pemphigoid
A 65-year-old woman had been recently diagnosed as having BP on the basis of a generalized pruriginous bullous eruption affecting predominantly the trunk and the limbs, and a compatible biopsy. Treatment with prednisone (60 mg Q.D.) was started and the skin lesions progressively improved within 3 weeks. After checking that thiopurine methyltransferase (TPMT) activity was normal, AZA (50 mg Q.D.) was introduced as a corticosteroid-sparing agent. One week later, well-tolerated fever along with several tender, dusky red-purple nodular subcutaneous lesions appeared on both lower legs []. There was no evidence of any other symptoms or clinical findings. Complete blood count, laboratory tests, and chest radiograph showed no abnormalities. Mantoux test was negative. Biopsy of a skin nodule was performed and histological examination revealed septal panniculitis with lymphocytic infiltration of the hypodermis [], findings highly suggestive of EN. Aside from prednisone and AZA, no other medications were administered at that time. Hypersensitivity reaction to AZA was suspected and the drug was discontinued, observing complete remission of the fever and EN within 2 weeks.