A case of mixed connective tissue disease with usual interstitial pneumonia and methotrexate-induced erythema multiforme.

Mixed connective tissue disease (MCTD) is a rare autoimmune disorder characterized by overlapping features of various connective tissue diseases. We present a case of a 62-year-old Indian male with a 20-year history of skin tightness and dysphagia, accompanied by a low-grade fever persisting for 1 year. Physical examination revealed sclerodactyly, Raynaud's phenomenon, and perioral sclerosis. High-resolution computed tomography findings indicated a pattern consistent with usual interstitial pneumonia (UIP), characterized by honeycombing and traction bronchiectasis. Laboratory tests confirmed the presence of anti-U1 RNP antibodies. The patient was initially treated with methotrexate, which led to bullous drug eruptions on the palms, lips, and soles, diagnosed as methotrexate-induced erythema multiforme. Following the discontinuation of methotrexate, treatment with mycophenolate mofetil and prednisolone resulted in the resolution of fever and synovitis within 1 month. Over 6 months, there was significant improvement in Raynaud's phenomenon and sclerodactyly. This case highlights the uncommon presentation of UIP in MCTD and the potential for methotrexate to induce bullous eruptions, emphasizing the necessity for cautious use of this medication in patients with connective tissue diseases.