Myositis‐related autoantibody profile and clinical characteristics stratified by anti‐cytosolic 5′‐nucleotidase 1A status in connective tissue diseases

Abstract

AbstractIntroduction/AimsCytosolic 5′‐nucleotidase 1A (cN‐1A) autoantibodies have been recognized as myositis‐related autoantibodies. However, their correlations with clinical characteristics and other myositis‐specific and myositis‐associated autoantibodies (MSAs/MAAs) are still unclear. We aimed to establish the prevalence and clinical and laboratory associations of cN‐1A autoantibodies in a cohort of patients with connective tissue diseases.MethodsA total of 567 participants (182 idiopathic inflammatory myopathies [IIM], 164 systemic lupus erythematosus [SLE], 121 systemic sclerosis [SSc], and 100 blood donors [BD]) were tested for the presence of cN‐1A autoantibodies and other myositis‐specific and myositis‐associated autoantibodies (MSAs/MAAs). Clinical and laboratory characteristics were compared between anti‐cN‐1A positive and negative patients with sporadic inclusion body myositis (sIBM) and between anti‐cN‐1A positive and negative patients with non‐IBM IIM.ResultsIn the sIBM cohort, 30 patients (46.9%) were anti‐cN‐1A positive vs. 18 (15.2%) in the non‐IBM IIM cohort, 17 (10%) were anti‐cN‐1A positive in the SLE cohort and none in the SSc or the BD cohorts. Anti‐cN‐1A positivity had an overall sensitivity of 46.9% and a specificity of 93.2% for sIBM. Dysphagia was more frequent in the anti‐cN‐1A positive vs. negative sIBM patients (p = .04). In the non‐IBM IIM group, being anti‐cN‐1A antibody positive was associated with the diagnosis polymyositis (p = .04) and overlap‐myositis (p = .04) and less disease damage evaluated by physician global damage score (p < .001).DiscussioncN‐1A autoantibodies were predominantly found in IIM patients and was associated with dysphagia in sIBM patients. Notably, anti‐cN‐1A appears to identify a distinct phenotype of anti‐cN‐1A positive non‐IBM IIM patients with a milder disease course.