Editors' note: Granulomatosis-associated myositis: High prevalence of sporadic inclusion body myositis

In the article “Granulomatosis-associated myositis: High prevalence of sporadic inclusion body myositis,” Dr. Dieudonné et al. examined the predictive significance of muscle granulomas in patients with myositis. They examined 23 patients with myositis and granulomas, 23 with myositis without granuloma, and 20 with sporadic inclusion body myositis (sIBM) without granulomas. They found that all but 2 patients with granulomatosis-associated myositis had extramuscular manifestations common in sarcoidosis that were systematically absent in the control groups and that half of these patients also met diagnostic criteria for sIBM with expected poor response to treatment. They concluded that patients with granulomatosis-associated myositis should be carefully screened for associated sIBM. In response, Drs. Liewluck and Alhammad cite similar findings in 2 prior publications. Noting that the majority of their patients with treatment-refractory granulomatous myositis had sarcoplasmic congophilic deposits, they posit that such deposits could indicate treatment refractoriness, regardless of whether the patients meet criteria for sIBM. They enquire whether the authors performed Congo Red staining for their samples, this being more widely available than the TDP43 and p62 immunostains mentioned in the paper. Responding to these comments, the authors note that Congo Red staining was performed in samples from 12 patients (48%), with sarcoplasmic congophilic deposits found in 2 patients who also met sIBM criteria and were treatment refractory, and agree that an epidemiologic study of the incidence of sIBM in sarcoidosis could be valuable. This exchange highlights the remarkable copathologies that are being uncovered in neuromuscular disease.