Granulomatous Myositis: Characteristics and Outcome from a Monocentric Retrospective Cohort Study

Granulomatous myositis is a clinical-pathological entity, which has been rarely reported, mostly described in sarcoidosis. Currently, no clear and simple prognostic factor has been identified to predict granulomatous myositis evolution. The clinical, anatomopathological, imaging, and biological characteristics of 26 patients with granulomatous myositis were retrospectively collected to describe clinical presentation and outcomes of this condition. Twenty-six patients with granulomatous myositis were included (14 males) with a median age of symptom onset of 65 years. 54% of patients presented a severe form of the disease defined as a Rankin score ≥2 at last follow-up visit or a progressive form of the disease (no improvement under treatment). Etiology were sarcoidosis (n=14), inclusion body myositis (n=4), autoimmune disease (n=1), hematological malignancy (n=1), and idiopathic (n=6). Distal deficit and amyotrophy were more frequent among those with a severe disease. Corticosteroids led to improvement in 75% of cases, but 66% of responders relapsed. Methotrexate appeared as a promising second line therapy with clinical improvement in 50% of patients, and no relapse in responders. Granulomatous myositis is often a severe and difficult-to-treat disease in which patients frequently progress towards severe disability. The presence of muscle atrophy and distal weakness appears to be frequently associated with a severe form of the disease.