Let’s Discuss: Insights from the ACR Convergence 2025 Review Course

For imaging mimics of myositis, it is important to consider the possibility of even rare entities, such as acute myonecrosis in diabetes (diabetic myonecrosis), a rare, spontaneous muscle infarction that causes sudden pain, swelling and tenderness, most often in the thigh. Muscle biopsies can be very helpful, such as for teasing apart immune-mediated necrotizing myopathies from antisynthetase syndrome, but reading pathologists can disagree, even when they are looking at the same slides. Myofibrillar myopathy can mimic IBM on muscle biopsy as both share similar features, such as rimmed vacuoles. Dysferlinopathy refers to a group of rare muscular dystrophies caused by recessive mutations in the DYSF gene, and these patients have muscle biopsies with inflammation that can be confused with that of polymyositis. Thus, every muscle biopsy should be evaluated within the clinical context, especially with attention paid to pattern of weakness, degree of CK elevation, presence or absence of myositis-specific antibodies and electromyography/nerve conduction study findings.

Jason Liebowitz, MD, FACR, is an assistant professor of medicine in the Division of Rheumatology at Columbia University Vagelos College of Physicians and Surgeons, New York.

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