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 patients with granuloma-myositis had extramuscular involvement, including signs common in sarcoidosis that were systematically absent in the control-myositis and the control-sIBM groups.