Refining the clinical and therapeutic spectrum of granulomatous myositis from a large cohort of patients.

Objectives: Granulomatous myositis (GM) is a rare entity whose precise clinical features and therapeutic outcomes have not yet been well defined. Given the limited evidence, data from a large cohort of patients is needed to aid in the recognition and management of this condition.

Methods: We retrospectively analyzed our institutional databases to identify patients who had myositis and non-caseating granuloma on muscle biopsy (GM). We collected data on clinical and diagnostic features, management, and outcomes of these cases and compared them with inclusion body myositis (IBM) controls.

Results: 22 GM patients were identified and subdivided into 3 main groups: 13 patients with GM and sarcoidosis (6 of whom subsequently developed suspected or confirmed IBM), 7 patients with idiopathic isolated GM (2 of whom subsequently developed confirmed IBM), 2 patients with GM and Crohn's disease. Patients with GM and sarcoidosis without IBM, as well as patients with isolated GM, exhibited variable clinical presentation ranging from myalgia to mostly symmetrical proximo-distal weakness, with most showing complete or at least partial response to therapies. Patients with GM associated with Crohn's disease had only mild clinical impairment and good therapeutic outcomes. Conversely, patients with GM and IBM presented more severe asymmetric proximo-distal muscle weakness, increased occurrence of dysphagia and poor treatment response, similar to IBM controls.

Conclusions: A frequent association of GM with IBM and/or sarcoidosis was demonstrated in our cohort. When associated with IBM, GM led to treatment refractoriness and more severe clinical impairment, unlike the other GM groups which showed satisfactory outcomes in most cases.