Two cases of dermatomyositis with anti-cN1A antibody positivity

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of autoimmune-mediated disorders. One of the most important developments in recent years regarding IIMs is the clinical use of myositis-specific antibodies and myositis-associated antibodies. The identification of anti-cytosolic 5’-nucleotidase 1A (anti-cN1A), one of the myositis-associated antibodies, represents significant progress in understanding inclusion body myositis (IBM), with research focusing on its role in predicting survival, diagnostic potential, clinical phenotype, and histopathological correlations. With the increasing use of autoantibodies in recent years, it is essential to understand their specificity and sensitivity properties. We presented two cases of dermatomyositis with positive anti-cN1A antibodies, which are known to have high specificity in IBM. One of the cases is a male patient, and IBM was included in the differential diagnosis because of anti-cN1A antibody positivity and resistance to first-line immunosuppressive therapy. The other case is a female patient diagnosed with dermatomyositis twelve years ago, with a myositis antibodies panel performed during a disease flare revealing anti-cN1A antibody positivity.