Clinical Features of Necrotizing Autoimmune Myopathy
Necrotizing autoimmune myopathy (NAM) is characterized pathologically by necrotic muscle fibers with absent or minimal inflammation. It is often accompanied by statin therapy, connective tissue diseases, cancer, and autoantibodies specific for signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR).
Mayo Clinic researchers, first author Margherita Milone, M.D., Ph.D., conducted a study published in JAMA Neurology to document the clinical, electrophysiologic, serologic, and pathologic characteristics of NAM, as well as treatment strategies and outcomes. Researchers attempted to identify differences among patients with NAM based on associated risk factors and potential determinants of outcome.
The study reviewed medical records for 63 adult patients assigned the clinical and histopathologic diagnosis of NAM. Clinical, electrophysiologic, and pathologic characteristics were collected and compared among patient subgroups. Predictors of response to treatment were identified by univariate logistic regression.
Based on the study results, NAM was idiopathic in half of the patient cohort with clinical and histopathologically defined disease. In the remainder, NAM was associated with statin medication, cancer, or connective tissue disease. One in four patients was SRP-IgG positive, and one in three was HMGCR-IgG positive. The disease was usually not controlled by corticosteroid monotherapy. Presentation, course, and outcomes did not differ significantly in seropositive, seronegative, and statin-associated cases. Early aggressive immunosuppressant therapy improved outcomes, and risk of relapse was high during medication dose reduction or withdrawal.
In summary, NAM is a severe immune-mediated myopathy that requires prompt recognition because early aggressive management can lead to favorable outcomes. Statin medications are the most commonly identified risk factor, but malignant tumors should be excluded.