Unusual organ involvement in sarcoidosis: sarcoid myopathy and peritoneal sarcoidosis.

Myopathy and peritoneal involvement are rare complications of sarcoidosis, and the latter can mimic malignancy with peritoneal dissemination. In this case, a patient with a history of polyarthritis and positive rheumatoid factor presented with proximal muscle weakness and abdominal pain. Biopsies of muscle and peritoneum revealed non-caseating granuloma suggesting sarcoidosis. Ocular and pulmonary involvement later developed and confirmed the diagnosis of sarcoidosis.