Clinicopathological features of sarcoidosis manifesting as generalized chronic myopathy

Although chronic myopathy has been reported to affect skeletal muscle in sarcoidosis, its clinicopathological features have not been fully elucidated. We characterized the clinical, histopathological, and prognostic features of eleven patients with sarcoidosis manifesting with chronically progressive, generalized myopathy that was confirmed with muscle biopsy. Generalized muscle weakness extending to the four extremities and trunk was the cardinal feature of these cases. Muscle atrophy was evident in nine patients, particularly in the lower limbs, whereas myalgia was reported in only two patients. Myopathy was the first manifestation of sarcoidosis in five patients. Only six patients showed elevated plasma creatine kinase levels. Using skeletal muscle computed tomography, the distribution of muscle atrophy was predominant in the hip adductors, knee flexors and ankle plantarflexors. Radiological assessments, including magnetic resonance imaging, gallium scintigraphy, and fluorodeoxyglucose positron emission tomography-computed tomography imaging, revealed findings suggestive of skeletal muscle inflammation in only half of the patients examined. However, in all patients, muscle biopsy specimens revealed an active inflammatory process, as observed by focal non-caseating epithelioid granuloma with predominant CD4-positive lymphocytic infiltration. Sarcolemmas were diffusely stained with HLA-ABC, HLA-DR and intercellular adhesion molecule-1 antibodies, suggesting diffuse and active antigen presentation. Functional improvement after immunomodulatory treatment was significantly better in patients with short disease durations (p < 0.05). The therapeutic response was poor in patients with long disease durations; thus, early diagnosis and early initiation of treatment are important.