AANEM News Express

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Science News: Dermatomyositis: Muscle Pathology According to Antibody Subtypes

Submitted by: Milvia Y. Pleitez, MD
Edited by: Vishwajit Hegde, MD

Tanboon J, Inoue M, Saito Y, et al. Dermatomyositis: Muscle pathology according to antibody subtypes. Neurology. 2022;98(7):e739-e749. doi:10.1212/WNL.0000000000013176

Summary: The classification criteria for dermatomyositis (DM) has evolved as dermatomyositis-specific antibodies (DMSAs) have been identified. 5 DMSAs included in serological criteria for DM per the European Neuromuscular Center in 2018 (ENMC 2018) include anti–transcription intermediary factor 1-γ (TIF1-γ), anti–complex nucleosome remodeling histone deacetylase (Mi-2), anti–melanoma differentiation gene 5 (MDA5), anti–nuclear matrix protein 2 (NXP-2), and anti–small ubiquitin-like modifier-activating enzyme (SAE).  Definitive pathological criteria for DM used by the 2018 ENMC-DM consensus included only perifascicular atrophy and the expression of myxovirus resistant protein in myofibers. Different clinical phenotypes have been described based on DMSAs present. This retrospective study of 256 muscle biopsies pathologically diagnosed with DM at the National Center of Neurology and Psychiatry in Japan over an 11-year period, evaluated the pathological features in DMSA specific MxA positive muscle biopsies.
Important findings from this study include the finding that MxA expression is more sensitive than perifascicular atrophy for diagnosing DM (100% vs. 49.6%). Phenotypes noted include anti-TIF1-γ DM associated with  DM skin lesions, dysphagia, and malignancy; anti-Mi-2 DM associated with high creatine kinase (CK) level, myalgia, and muscle weakness; anti-MDA5 DM associated with mechanic hands and interstitial lung disease (ILD) but low CK levels and less muscle involvement; and anti-NXP-2 DM with muscle weakness but less skin involvement.
Other findings of note include the finding that anti-Mi-2 and anti-TIF1 γ were seen in adult patients whereas anti-NXP-2 was seen in juvenile patients. Also of importance was the finding that anti-TIF-1 γ was associated with malignancy and anyone diagnosed with DM below the age of 40 merits a malignancy workup.
From a pathological standpoint, those biopsies with non-TIF1-γ DM antibodies, anti-TIF1-γ DM was associated with vacuolated/punched-out fibers (64.7% vs non-TIF1-γ 34.3%; p < 0.001). Anti-NXP-2 DM cases were associated with microinfarction (26.5% vs non-NXP-2 9.3%; p < 0.001).
These findings suggest that the pathophysiology for these subtypes may be different and including testing for DMSAs may help classify subtypes of DM.

Comments: This study provides good evidence for DM subtypes and importantly shows that we should be including myxovirus resistant protein expression in our evaluation of muscle biopsies for DM.

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