Myopathy with anti-signal recognition particle antibodies: clinical and histopathological features in Chinese patients.

Myopathy with anti-signal recognition particle antibodies (SRP) is generally thought to be immune-mediated necrotic myopathy in previous studies. We report the clinical and histopathological features of myopathy with anti-SRP antibodies in Chinese patients. Muscle biopsy and immunoblots for myositis antibodies were carried out in 123 patients with idiopathic inflammatory myopathy. Among them, 16 (13.0%) patients had anti-SRP antibodies. Age of onset ranged from 24 to 77 years, and the disease began insidiously. Fourteen of 16 patients presented with chronic progression of proximal limb weakness, with 6 having myalgia. Serum creatine kinase levels ranged from 400 to 9082 IU/L. Muscle biopsies showed necrotic and/or regenerative muscle fibers in all 16, infiltrates of lymphocytes in 11 and morphological features of muscular dystrophy in 7. Eleven patients showed focal or diffuse major histocompatibility complex class 1 expression in sarcolemma or cytoplasm of muscle fibers, with 9 showing deposition of membrane attack complex in necrotic muscle fibers and 2 around capillaries. These findings indicate that anti-SRP antibodies are most likely to be related to IMNM. Myopathy with anti-SRP antibodies is not infrequent in Chinese patients with idiopathic inflammatory myopathy.