Ultrasonographic assessment of the distal interphalangeal joints in psoriatic arthritis and osteoarthritis of the hand: definition and prevalence of elementary lesions to support differential diagnosis

The distal interphalangeal (DIP) joints of the hand are frequently involved in both psoriatic arthritis (PsA) and osteoarthritis (OA), including its erosive variant (EHOA). Differentiating PsA from OA based on clinical features remains challenging, especially when conditions coexist. Ultrasound (US) is valuable for assessing inflammatory and structural changes, thus supporting the differential diagnosis. Our aim as to define and validate US-detected elementary lesions of the hand DIP to support the differential diagnosis between PsA, nodal OA, and EHOA. A Delphi exercise was conducted to identify and score elementary lesions at the DIP. Reliability was tested via a web-based static image exercise. Subsequently, 110 patients (47 PsA, 38 EHOA, 25 OA) were assessed in a cross-sectional study, and the prevalence of the lesions was compared across groups. The Delphi identified synovitis, tenosynovitis, enthesitis, soft tissue oedema, and bone erosions as relevant lesions. Reliability was high for most lesions, with inter-reader kappa ranging from 0.613 for enthesitis to 0.938 for power Doppler synovitis. In the clinical cohort, PsA patients exhibited higher prevalence of tenosynovitis (76.59% vs 15.8%, p<0.0001), power Doppler synovitis (95.74% vs 51.14%, p<0.0001), soft tissue oedema (91.94% vs 66.67&, p=0.0018), and extensor (89.36% vs 36.51%, p<0.0001) and flexor (61.7% vs 23.81%, p=0.0001) enthesitis compared to OA. Bone erosions were more frequent in EHOA (94.74% vs 42.55%, p<0.0001). The findings at the patient and joint level were consistent. US-detected inflammatory lesions at DIP, particularly synovitis, tenosynovitis, and enthesitis, are more prevalent in PsA than OA. These features may support the differential diagnosis.