Background: Non-radiographic axial spondyloarthritis (nr-axSpA) data from South America are scarce, especially regarding image features. ObjectiveTo estimate the frequency of nr-axSpA and ankylosing spondylitis (AS) in a cohort of Argentinian patients with chronic low back pain (LBP) and to analyze the difference between both, with focus on magnetic resonance imaging (MRI) lesions, at diagnosis. Methods:Patients with LBP and a diagnosis of axSpA who participated in a reumacheck program were included. All patients with a suspicion of SpA were evaluated using blood analytics, HLA-B27, and images (MRI). Sociodemographic data, SpA features, diagnostic dela,y and clinimetrics were assessed by an operator who was blinded to the patient's test results. On MRI, the presence of SpA lesions was assessed and a concordance exercise was carried out between rheumatologists and radiologist.Result: Of 198 LBP patients, 97 had axSpA, 54% of whom were nr-axSpA. A positive MRI was found in 50%. No difference in terms of disease activity, functional impact, laboratory or treatments between nr-axSpA and AS were found. Higher frequencies of male sex and chronic lesions on sacroiliac MRI were found in AS patients. In the logistic regression, an independent association with AS diagnosis was found: male (odds ratio [OR] 4.8), MRI fat replacement (OR 4.6), MRI sclerosis (OR 7.6), and diagnostic delay of more than 2 years (OR 10). The concordance between rheumatologists and radiologists was considered good to very good (κ 0.7-0.8). Conclusion:The frequency of nr-axSpA was 54%. We found a higher frequency of being male, more SpA features, and a longer diagnostic delay in patients with AS.Patients with AS had more structural lesions, with a good concordance between rheumatologist and radiologist.

Objective: Most patients with psoriatic arthritis begin with cutaneous psoriasis, which is why all early detection strategies are based on screening in the dermatological consultation and referral to a rheumatologist. However, there are cases of patients who consult initially for musculoskeletal symptoms, mostly joint pain, regardless of family and/or personal history of psoriasis. This study aimed to estimate the frequency of psoriatic arthritis in a cohort of patients who consulted for polyarthralgia and to determine the differential features, at the time of clinical presentation, in relation to both patients with final diagnosis other than psoriatic arthritis and patients with diagnosis of rheumatoid arthritis. Methods: Consecutive patients with polyarthralgia (including arthralgia of the hands) were included. Clinical examination, laboratory tests, ultrasound with power Doppler of both hands, and radiography of both hands and feet were performed at baseline. All patients were followed up and the definitive diagnosis of psoriatic arthritis was established. Results: A total of 1055 were included, 88 (8.3%) ended with diagnosis of psoriatic arthritis. Diagnosis of psoriatic arthritis was positively associated with a family history of psoriasis (odds ratio = 4.14), psoriasis (odds ratio = 78.94), radiographic erosions (odds ratio = 5.74), and ultrasound with at least 1 joint with positive power Doppler (odds ratio = 7.11). In comparison with rheumatoid arthritis patients, diagnosis of psoriatic arthritis was positively associated with psoriasis (odds ratio = 433.42) and family history of psoriasis (odds ratio = 41.63). On the other hand, it was negatively associated with positivity, for both rheumatoid factor (odds ratio = 0.03) and anti-cyclic citrullinated peptide antibodies (odds ratio = 0.06). Conclusion: The frequency of psoriatic arthritis was 8.3% and was associated with a personal and/or family history of psoriasis, radiographic erosions, and inflammatory involvement by Power Doppler Ultrasound (PDUS). In comparison with rheumatoid arthritis patients, psoriatic arthritis was associated with a personal and/or family history of psoriasis, while the presence of both rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies was shown to be a protective factor for the diagnosis of psoriatic arthritis.