Study Offers Overview of Features, Outcomes, Treatment for Immune-Mediated Necrotizing Myopathy

Lilian Vilar, DO
Credit: American College of Physicians

New data from the Congress of Clinical Rheumatology (CCR) East 2023 annual meeting is offering clinicians with a snapshot of the clinical features of immune-mediated necrotizing myopathy.

A retrospective review of data from patients with idiopathic inflammatory myopathy recorded over more than decade, results of the study provide an overview of patient characteristics, outcomes, and treatments relative to their counterparts with other forms of idiopathy inflammatory myopathies, such as dermatomyositis, cancer-associated myositis, and polymyositis.

First described in 2004, immune-mediated necrotizing myopathy represents a relatively new disease and is characterized by muscle cell death leading to weakness of the skeletal muscles on both sides of the body. According to the Myositis Support and Understanding Association, the disease effects an estimated 6300 people in the US, with this patient population ranging from children to middle-aged patients. As a result, the inflammatory myopathy poses a significant clinical challenge in both diagnosis and management.²

Led by Lilian Vilar, DO, a rheumatology fellow at the Walter Reed Medical Center, and Ian Ward, MD, of the Dwight D. Eisenhower Army Medical Center, the study leveraged data recorded within the Department of Defense database using ICD-10 codes to identify patients with inflammatory myositis between Jaunty 2006-December 2020. For inclusion in the analysis, patients were required to meet either the Bohan and Peter 1975 or EULAR/ACR classification criteria for definite or probable myositis.¹

For the purpose of analysis, patients were classified into 1 of 5 subtypes: immune-mediated necrotizing myopathy, anti-synthetase syndrome, dermatomyositis, cancer-associated myositis, and polymyositis. Investigators noted the last 4 were grouped into a combined myositis cohort.¹

Investigators pointed out Chi square tests were performed to analyze categorical variables and Student’s t-tests were used to account for continuous variables between the immune-mediated necrotizing myopathy and combined myositis cohort. Outcomes of interest for the investigators’ analyses differences in demographic, clinical, and serologic parameters as well as treatments and outcomes between the study cohorts.¹

Overall, a total of 195 patients with follow-up time ranging from 1-180 months were identified for inclusion. Of these, 42 were placed in the immune-mediated necrotizing myopathy cohort and 153 were in the combined myositis cohort. Comparison of demographic factors suggested those in the immune-mediated necrotizing myopathy had a greater mean age (60.2 vs 48.2 years; P <.0001) and were more likely to be men (69% vs 37%; P=.0002) than those in the combined myositis cohort.¹

Further analysis indicated those in the immune-mediated necrotizing myopathy cohort had increased levels of mean creatine kinase levels (10,800 vs 5140 U/L; P <.0001), mean aldolase levels (67.9 vs 37.1 U/L; P=.0036), and a higher proportion of patients with myoglobinuria (57% vs 23%; P=.0001). Investigators also called attention to an apparent lack of interstitial lung disease among the immune-mediated necrotizing myopathy cohort.¹

When examining trends in treatment, results indicated methotrexate (P=.027) and IVIG (P=.0009) were more commonly used in induction treatment of immune-mediated necrotizing myopathy. Additionally, there were no significant differences in outcomes with similar rates of drug free remission, all remission, and active disease between cohorts.¹

“Despite the different demographic and clinical features at presentation, all idiopathic inflammatory myopathy groups displayed similar clinical outcomes. Immune-mediated necrotizing myopathy stands out as a clinically severe entity, however has comparable treatment responsiveness with other forms of myositis,” wrote investigators.¹

References:

1. Vilar L, Ward IM. Clinical features of immune-mediated necrotizing myopathy: a retrospective review of patients diagnosed within the military healthcare system. Paper presented at: Congress of Clinical Rheumatology (CCR) East 2023 Annual Meeting. Destin, FL. May 4 – 7, 2023.
2. Immune-mediated necrotizing myopathy (IMNM). Myositis Support and Understanding. Accessed May 8, 2023. https://understandingmyositis.org/myositis/necrotizing-autoimmune-myopathy/.