Granulomatosis-associated myositis: High prevalence of sporadic inclusion body myositis

Objective To refine the predictive significance of muscle granuloma in patients with myositis. Methods A group of 23 patients with myositis and granuloma on muscle biopsy (granuloma-myositis) from 8 French and Belgian centers was analyzed and compared with (1) a group of 23 patients with myositis without identified granuloma (control-myositis) randomly sampled in each center and (2) a group of 20 patients with sporadic inclusion body myositis (sIBM) without identified granuloma (control-sIBM). Results All but 2 granuloma-myositis patients had extramuscular involvement, including signs common in sarcoidosis that were systematically absent in the control-myositis and the control-sIBM groups. Almost half of granuloma-myositis patients matched the diagnostic criteria for sIBM. In these patients, other than the granuloma, the characteristics of the myopathy and its nonresponse to treatment were similar to the control-sIBM patients. Aside from 1 patient with myositis overlapping with systemic sclerosis, the remaining granuloma-myositis patients did not match the criteria for a well-defined myositis subtype, suggesting pure sarcoidosis. Matching criteria for sIBM was the sole feature independently associated with nonresponse to myopathy treatment in patients with granuloma-myositis. Conclusion Patients with granuloma-myositis should be carefully screened for sIBM associated with sarcoidosis in order to best tailor their care.