PsOut syndrome as a topical problem of modern rheumatology: difficulties of differential diagnosis (clinical case)

Hryn V.K.¹, Rekalov D.G.¹, Samsonenko S.V.^2,3, Krupko V.V.³

• ¹State Institution «National Scientific Center “M.D. Strazhesko Institute of Cardiology, Clinical and Regenerative Medicine of the National Academy of Medical Sciences of Ukraine”, Kyiv
• ²Dnipro State Medical University, Dnipro
• ³Professor Rekalov Clinic of Rheumatology, Dnipro

Summary. The coexistence of psoriatic arthritis (PsA) and gout, known as PsOut syndrome, is a novel and insufficiently studied clinical concept in modern rheumatology. The increasing prevalence of this comorbid condition is driven by shared pathogenetic mechanisms, including chronic systemic inflammation, activation of IL-1 and the IL-17/23 axis, metabolic disturbances, and hyperuricemia. The complexity of differential diagnosis between PsA flare and gouty arthritis often leads to delayed diagnosis verification and suboptimal treatment. The objective. To draw attention to PsOut syndrome as a relevant clinical issue and to analyze the challenges of differential diagnosis based on a clinical case.Clinical case. We present the case of a 62-year-old man with a long-standing history of psoriatic arthritis (since 2021), who had been treated with methotrexate. In 2024, gout was diagnosed for the first time in the setting of marked hyperuricemia (maximum serum uric acid level up to 780 μmol/L). In April 2026, the patient presented with another exacerbation manifested by severe pain and limited range of motion in the right knee and ankle joints. Clinical examination revealed polyarticular involvement with joint deformities, Heberden’s nodes, and enthesopathy. Laboratory findings demonstrated serum uric acid 538.5 μmol/L, C-reactive protein 6.6 mg/L, and hypercholesterolemia. Synovial fluid analysis of the right knee joint revealed isolated monosodium urate crystals. The final diagnosis was PsOut syndrome (psoriasis, psoriatic arthritis, and gout) with concomitant generalized osteoarthritis. Conclusions. PsOut syndrome is a clinically significant comorbid condition that requires a high level of awareness among rheumatologists. In patients with PsA and hyperuricemia, synovial fluid analysis is recommended to exclude a gout component. Early recognition of this combined pathology allows optimization of treatment and prevention of progressive structural joint damage.