Granulomatous Myopathy in Patients with Sarcoidosis and Myasthenia Gravis

Overview

Granulomatous myopathies are extremely rare. The finding of epithelioid granulomas in muscle biopsy indicates mostly an involvement of the skeletal muscle in systemic sarcoidosis. In this report we provide description of five patients with previously diagnosed sarcoidosis (pulmonary or cutaneous), in which a clinically significant muscle weakness developed. We aim at demonstrating the value of muscle biopsy for further treatment of the patients, since clinically indistinguishable myopathies can arise not due to the involvement of muscles in the granulomatous process, but due to the corticosteroid-induced changes (chronic steroid myopathy). The demonstration of a selective atrophy of type II muscle fibers can provide the clue for distinguishing the patients, in which the corticosteroid treatment should continue, from those, in which the treatment should be modified. Further, we discuss a rare finding of granulomas in muscle biopsies of two patients with myasthenia gravis (MG) associated with thymoma. Although it is difficult to explain the pathogenesis of this event, MG should be considered in the differential diagnosis of granulomatous myopathies. Moreover, the finding of granulomas along with lymphocytic infiltration in MG muscle should lead to a search for an underlying thymic neoplasm.

Key words:
myopathy – granulomas – sarcoidosis – myasthenia gravis