Background/Purpose: Anti-NOR 90 antibodies have been detected in inflammatory conditions, neoplastic diseases and even in healthy individuals. Despite numerous epidemiologic studies, large scale studies are not available and the clinical relevance of the Anti-NOR 90 antibodies remains unclear. This antibody tends to be found in Systemic Sclerosis (SSc), overlap syndromes, as well as in other systemic autoimmune rheumatic diseases (SARD). Anti-NOR 90 can be found in 4.8% of patients with SSc and it may be considered a marker of limited cutaneous SSc and mild involvement of internal organs. Not all published studies agree about its specificity in SARD. The aim of this study is to identify the clinical and analytical manifestations associated with the presence of Anti-NOR90 in patients with SARD.

Methods: A retrospective study of patients with Anti-NOR90 positivity (detected by immunoblot assay), observed from january 2017 to december 2021, from a single rheumatology outpatient centre, was included. Demographic, clinical, and immunological data at presentation and during follow-up were collected. A descriptive analysis was made. All patients diagnosed with a SARD satisfied the ACR classification criteria for the particular disease.

Results: Forty patients were positive for anti-NOR90. SARD was diagnosed in 30% of the patients (SSc: n=3; undifferentiated connective tissue disease: n=3; spondyloarthritis: n=2; polymyalgia rheumatica: n=1; rheumatoid arthritis: n=1; sjogren´s disease: n=1; systemic lupus erythematous: n= 1), 7.5% had other autoimmune disease (primary biliary cholangitis: n=2; autoimmune tiroiditis: n=1) and 62.5% had no pathologic conditions. In the SARD group, 58.3% were female and the median age was 49.2 ± 11.2 years. The most frequent presenting clinical features was inflammatory arthralgias (50%), followed by Raynaud phenomenon (16%), arthritis (8.3%), photosensitivity (8.3%), sclerodactyly (8.3%) and xerostomia (8.3%). During follow-up, musculoskeletal involvement was present in 41.6% (n=5) of the patients, peripheral vascular involvement (detected by nailfold capillaroscopy) in 33% (n=4), gastrointestinal (esophageal hypomotility) and lung involvement (interstitial lung disease) was detected in 16% (n=2) and 8.3% (n=1) of the patients, respectively. Half of the SARD patients showed other antibodies specificities: anti-centromere (n=3), anti-Ku (n=1), anti-SSB (n=1), anti-fibrillarin (n=1), anti-PM/Scl (n=1), anti-ribosomal P (n=1). Persistent elevated inflammatory markers were present in 58.3%, leucopenia in 16% and low complement levels in 8.3%.

Conclusion: Anti-NOR 90 is associated with multiple SARD (most common in SSc and undifferentiated connective tissue disease) and with a heterogeneity of clinical manifestations Musculoskeletal and peripheral vascular symptoms were the most prevalent associated clinical features in both initial clinical presentation and during follow-up.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/anti-nor-90-antibodies-what-is-the-clinical-significance-in-rheumatic-inflammatory-conditions/