Idiopathic granulomatous myositis: does the clinical spectrum include polymyalgia rheumatica?

Granulomatous inflammation restricted to muscle is an uncommon cause of myopathic syndromes. Two patients were diagnosed with idiopathic granulomatous polymyositis after appropriate investigations failed to reveal a systemic or alternative explanation for the granulomas seen in their muscle biopsy. One patient presented with a syndrome indistinguishable from polymyalgia rheumatica but both patients manifested disabling myalgias which were strikingly corticosteroid responsive. The two cases underscore the potential importance of muscle biopsy in polymyalgic states, the non-specificity of polymyalgia rheumatica as a syndrome which can be simulated by other disorders including granulomatous myositis, and the potential corticosteroid responsiveness of prominent, functionally limiting myalgias which can be seen in this disorder. Some controversy continues regarding the correct nosology of this disease, largely perpetuated by an awareness of the inherent limitations of current non-invasive evaluation techniques to confirm occult granulomatous involvement of non-myogenous organs.