P82 Are nail, scalp and intergluteal cleft psoriasis really risk factors for psoriatic arthritis or are we just repeating previous studies?

Abstract Psoriasis is a chronic, inflammatory, immune-mediated, systemic disease that primarily affects the skin and joints. In ∼70% of cases, the skin comes before the joints, and it is believed that ∼30% of patients with psoriasis will develop psoriatic arthritis (PsA). There is an ongoing effort to identify screening tools and biomarkers that detect joint disease early. Known risk factors include early onset and severity of disease, nail, scalp and intergluteal cleft involvement, family history of PsA, HLA-B27 positive, obesity, uveitis, biomechanical stress, and trauma. Observational, cross-sectional study with severe plaque psoriasis patients, aged between 18 and 70 years, of both genders. Non-probabilistic convenience sample: All patients were evaluated by the same board-certified dermatologist. Over 3 months, during the weekly shift of the severe psoriasis clinic, PEST was applied. Clinical and epidemiological variables were collected on medical records. PsA was defined by CASPAR criteria. It underwent an ethical assessment and was approved. Hundred and fifty-eight patients were studied: average age of 50.84 years, with a predominance of females (53.2%). The average duration of the disease was 15.89 years. Mean psoriasis area and severity index and body surface area were, respectively, 16.65 and 20.88%. Fifty patients (31.6%) with PsA were identified. Regarding PEST, a sensitivity of 84.61%, a specificity of 75.47%, with a negative predictive value of 90.90% were identified. Having a positive PEST made the presence of PsA almost seven times more frequent [PR: 6.914, P < 0.0001, 95% confidence interval (CI) = 3.486–13.714]. Scalp (80.9%) and intertriginous/intergluteal cleft psoriasis (55.1%) was frequent in the sample, but did not correlate with the presence of PsA (PR: 1.113, P = 0.794, 95% CI = 0.523–2.454; and PR: 0.881, P = 0.612, 95% CI = 0.565–1.375, respectively). However, nail involvement was significantly related to PsA (PR: 1.669, P = 0.026, 95% CI = 1.071–2.601). PEST performance was consistent with the literature and was especially valuable in ruling out PsA due to its high negative predictive value. A classic study that correlates the involvement of specific sites with joint disease may present a selection bias, since it was conducted within the scope of rheumatology, focusing on patients with seronegative chronic inflammatory arthritis, where the diagnosis of psoriasis was not obvious, being sought in ‘hidden’ areas. After all, apart from the involvement of the nail matrix as an extension of distal interphalangeal enthesitis, what would be the biological relationship between the involvement of the scalp or even the intergluteal cleft and the presence of arthritis? Small sample, cross-sectional design and the fact that only 66% of patients with PsA had the opportunity to confirm their diagnosis with a rheumatologist are recognized limitations.