Diagnosis and differential diagnosis of granulomatous myositis

Granulomatous myositis is a rare neuromuscular disorder histologically characterized by the development of endomyseal and/or perimyseal granulomas. Clinical hallmarks are generalized muscle weakness, myalgias, and bulbar symptoms. The association of granulomatous myositis with sarcoidosis is well known; less recognized is the association with several infectious diseases, inflammatory bowel diseases, malignancy, thymoma, graft-vs-host disease, and myasthenia gravis. In absence of sarcoidosis or other underlying disorders, the diagnosis of isolated or primary granulomatous myositis must be considered. Therapeutic strategies focus on immunosuppression, whereas the therapy response is unpredictable. Here we discuss the clinical features, diagnosis, and differential diagnosis and therapeutic strategies of primary and secondary granulomatous myositis.