Dermatomyositis

DIAGNOSIS

The classification of antisynthetase syndrome (ASS) and dermatomyositis (DM) remains a subject of debate, with recent studies highlighting both distinct and overlapping features between the two conditions. A retrospective cohort study utilizing the ARUP Extended Myositis Panel found that DM patients had higher ANA titers, while ASS patients had a higher prevalence of anti-SSA antibodies and increased risk of interstitial lung disease (ILD). (37391068) Another study identified significant clinical overlap, with 32-44% of ASS patients exhibiting DM-like skin manifestations such as Gottron’s sign and heliotrope rash, challenging traditional diagnostic boundaries. (39306001) Editorial commentary emphasizes that serologic testing is critical for accurate classification, but no single antibody reliably differentiates between DM and ASS. (37379902) Furthermore, while MDA-5 positivity in DM strongly correlates with ILD, its role in ASS remains unclear. Given these findings, experts suggest that DM and ASS may exist on a spectrum, rather than as entirely separate diseases. This classification challenge has implications for treatment, clinical trial enrollment, and insurance coverage, necessitating a more flexible diagnostic approach.

The International Myositis Assessment and Clinical Studies Group published guidelines for idiopathic inflammatory myositis (IIM) cancer screening (37945774), below. An external validation study demonstrated 100% sensitivity with the application of these guidelines. However, it also demonstrated low specificity (numerical value not provided). The overall cancer rate in the 370 adult cohort was 4.9%. More than half the cancers were diagnosed prior to DM diagnosis and of those detected after DM diagnosis most were detected with age-appropriate cancer screenings. Yet, 90% of the cohort was identified as elevated risk (intermediate or high). (39320903)