Clinical characteristics in antibody-positive pediatric patients with immune-mediated necrotizing myopathy

OBJECTIVE: To investigate the clinical characteristics and therapeutic strategies of childhood immune-mediated necrotizing myopathy (IMNM) and to provide evidence for clinical diagnosis and management. METHODS: This single-center retrospective study analyzed the clinical data of 10 children diagnosed with antibody-positive IMNM at the Children's Medical Center, Xiangya Hospital, Central South University, from January 2016 to May 2025. The onset features, clinical manifestations, laboratory findings, muscle magnetic resonance imaging (MRI) characteristics, treatment modalities, and prognosis were summarized. RESULTS: Among the 10 patients, 4 were male and 6 were female, with a median age at onset of 5.5 years (range: 3-16 years). The main clinical manifestations included symmetric proximal muscle weakness (100%) and cutaneous manifestations (50%, including Gottron's sign and periorbital rash). Creatine kinase (CK) levels were markedly elevated, with a median of 3988.5 U/L (range: 2080-13524 U/L). Muscle MRI revealed edema or fatty infiltration in the thigh muscles. Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies were detected in 4 patients (40%), and anti-signal recognition particle (SRP) antibodies in 6 patients (60%). Electromyography (EMG) showed myopathic changes in all tested cases (8/10 patients). Muscle histopathology was available for one patient, demonstrating myofiber necrosis, regeneration, and inflammatory cell infiltration. All patients received glucocorticoid therapy, combined with oral methotrexate. Additionally, 5 patients were treated with rituximab, and 9 patients received intravenous immunoglobulin (IVIG). During follow-up, 2 patients achieved complete remission, 1 patient showed partial remission, 3 patients exhibited no significant remission, and 4 patients experienced relapse. CONCLUSION: Childhood IMNM is characterized by proximal muscle weakness, typical rash, and significantly elevated CK levels, frequently accompanied by anti-SRP or anti-HMGCR antibodies. Early immunosuppressive therapy, including glucocorticoids combined with immunosuppressants or IVIG, may be associated with clinical improvement in this small retrospective series.