Analysis on clinical features of necrotizing autoimmune myopathy

Abstract

Objective To investigate the clinical manifestations and auxiliary examination features of necrotizing autoimmune myopathy (NAM). Methods According to the inclusion criteria from European Neuromuscular Center (ENMC) International Workshop on idiopathic inflammatory myopathies published in 2004, 57 patients were diagnosed as NAM from 107 patients with necrotizing myopathy (NM). The risk factors, clinical symptoms, laboratory tests, electrocardiography (ECG), electromyography (EMG), skeletal muscle MRI and muscle pathology were retrospectively analyzed. Results There were more female patients than male patients (male∶female = 1.00∶1.59), with the peak onset age during 40 to 59 years old (43.86% , 25/57) in this study. Clinical types included idiopathic NAM, NAM with connective tissue disease, statin-associated NAM and NAM with cancer. Muscle weakness mainly affected proximal muscle, while it may simultaneously affect distal muscle (28.07% , 16/57). Serum creatine kinase (CK) elevated apparently (420-15 320 U/L). Serum anti-signal recognition particle (SRP) antibodies were detected in 24 out of 44 patients (54.55%). A total of 41 in 45 patients (91.11%) were detected myogenic damage on EMG, and 15 patients (33.33%, 15/45) also had spontaneous potentials. Thigh muscle MRI showed edema in 25 out of 27 patients (92.59% ) and fatty infiltration in 16 out of 27 patients (59.26% ). Other than necrotic fibers, major histocompatibility complex-1 (MHC-1) on sarcolemma were positive in 98.25% (56/57) cases, and membrane attack complex (MAC) deposition on capillary walls was detected in 92.98% (53/57) cases. Conclusions NAM can happen in all ages, mainly during 40 to 59 years old. Idiopathic NAM is the main type. Its main manifestation involves weakness of proximal muscle, sometimes with distal muscle. Extra-muscle symptoms are rare. Serum anti-SRP antibodies are common in NAM and edema is prominent change in thigh MRI.

DOI: 10.3969/j.issn.1672-6731.2016.10.009