AB1539 PREVALENCE OF ANTI-CN1A ANTIBODIES AND ITS CLINICAL SIGNIFICANCE – A RETROSPECTIVE MONOCENTRIC STUDY

Abstract

BackgroundAnti-cytosolic 5’-nucleotidase 1A (anti-cN1A) antibodies have recently been proposed as a biomarker for inclusion body myositis (IBM). With high specificity (87-100%), they can help differentiate IBM from other myositis.[1,2]Besides IBM, it has been detected in other inflammatory conditions. Recently, a higher prevalence of IBM has been associated with Sjogren Syndrome (SS), and anti-cN1A has been associated with myositis in SS, regardless of the subtype of myositis.[3]However, it can also be detected in healthy individuals and despite its high specificity in IBM, it may not be a useful biomarker for the diagnosis of autoimmune conditions.[4]Thus, the clinical relevance of anti-cN1A remains unknown.ObjectivesThe aim of this study was to identify the clinical and laboratory manifestations associated with the presence of anti-cN1A.MethodsA retrospective study of patients with anti-cN1A positivity (detected by immunoblot assay), observed from January 2021 to December 2022, in a tertiary hospital, was conducted. Demographic, clinical and immunological data were collected. A descriptive analysis was made.ResultsSixty-five patients were positive for anti-cN1A: 53 women (81.5%) and the median age was 47.2±14.9 years. Rheumatic inflammatory diseases were diagnosed in 15 (22.7%) patients, of which 5 had systemic lupus erythematosus (SLE), 4 had SS, and 1 with rheumatoid arthritis, polymyalgia rheumatica, granulomatosis with polyangiitis, juvenile idiopathic arthritis, spondyloarthritis and undifferentiated connective tissue disease. Eight (12.1%) patients had autoimmune thyroiditis, without known rheumatic diseases associated. The presence of anti-cN1A was also found in the context of infection in 7 (10.6%) patients and malignancy in 2 (3.0%) patients. Half of the patients (50.8%) patients were healthy individuals. No diagnosis of IBM or other myositis was made. Twenty-nine (44.6%) patients showed other antibodies specificities: anti-SSA/Ro52 (20%), anti-Ku (4.6%), anti-Mi-beta2 (4.6%) and anti-DSF70 (4.6%). In the SLE and SS groups, the most frequent presenting clinical features were sicca syndrome (66.7%), lymphopenia (9.2%), arthritis (6.1%) and photosensitivity (3.1%). No patient had signs or symptoms of muscular involvement.ConclusionAnti-cN1A was detected in diverse rheumatic conditions, but also in autoimmune thyroiditis and mostly in healthy individuals. SLE and SS were the most frequent systemic autoimmune rheumatic diseases associated with these antibodies. Contrary to expectations, no diagnosis of IBM or myositis was made. Further studies regarding the clinical significance of anti-cN1A are needed to attribute the real diagnostic value of this marker.