Immune-Mediated Necrotizing Myopathy: Evolving Insights, Current Understanding, and Future Directions for Myopathologic Diagnosis.

Context.—: Immune-mediated necrotizing myopathy (IMNM) is a relatively recently recognized subset of idiopathic inflammatory myopathies (IIMs). Understanding the historical context, current classification, typical pathologic features, and current diagnostic challenges for IMNM is essential for the diagnostic pathologist as the entity continues to evolve. Objective.—: To review pertinent literature on IMNM, emphasize its historical background and the current understanding, elucidate key characteristics in its myopathologic diagnosis, and guide future research efforts. Data Sources.—: Pertinent literature from a PubMed query on IIMs and IMNM from 1863 to 2025 is reviewed. Conclusions.—: Recognition of IMNM as a distinct IIM subtype has advanced through the serologic discovery of myositis-specific antibodies and the 2016 European Neuromuscular Centre consensus on IMNM. Nevertheless, challenges persist, particularly in the accurate characterization of seronegative IMNM, limitations in the current clinical criteria for IIMs, and conflicting data on potentially useful markers like p62 immunohistochemistry. A multifaceted approach integrating clinical, serologic, and pathologic data is essential in the continued research to refine the myopathologic diagnosis of IMNM.