Isolated Bilateral Gastrocnemius Myositis in Crohn Disease Successfully Treated with Adalimumab.

Extraintestinal manifestations are common in inflammatory bowel disease; however, muscular involvement in Crohn disease is rarely reported. We present a case of a 26-year-old male with ileocolonic Crohn disease who developed sudden tenderness in both calves. Doppler ultrasound was negative for deep vein thrombosis. Magnetic resonance imaging of the gastrocnemius muscle showed high intensity signal in the muscle fibers, and muscle biopsy demonstrated nonspecific lymphocytic myositis. Other relevant laboratory results included normal antineutrophil cytoplasmic antibodies and creatine kinase as well as elevated C-reactive protein, erythrocyte sedimentation rate, and anti- IgG titer. The patient was in clinical remission, being treated with azathioprine 2.5 mg/kg. Prednisone 60 mg/day was initiated with rapid resolution of calf tenderness; however, tenderness soon returned when the dose was tapered to 10 mg/day. Subsequently, prednisone and azathioprine were discontinued, and adalimumab was started at standard induction and maintenance doses. The patient's symptoms resolved shortly after the first induction dose. A repeat magnetic resonance imaging of the calves - 3 months after starting adalimumab - showed complete resolution of muscle inflammation. To our knowledge, this is the first case of gastrocnemius myositis - a rare extraintestinal manifestation of Crohn disease - successfully treated with anti-tumor necrosis factor agents.