Evaluating current definitions of low disease activity in psoriatic arthritis using ultrasound

Abstract Objective To evaluate low disease activity (LDA) cut-offs in psoriatic arthritis (PsA) using ultrasound. Methods Eighty-three PsA patients underwent clinical and ultrasound examinations at two visits. LDA was assessed using the Disease Activity index for Psoriatic Arthritis (DAPSA ⩽ 14), the Psoriatic ArthritiS Disease Activity Score (PASDAS ⩽ 3.2), the Composite Psoriatic Disease Activity Index ⩽ 4, the DAS28-CRP ⩽ 2.8 and the minimal disease activity criteria. Ultrasound was performed at 68 joints and 14 entheses. Minimal ultrasound disease activity (MUDA-j/e) was defined as a Power Doppler score ⩽ 1, respectively at joints, paratendinous tissue, tendons and entheses. A global ultrasound score was calculated by summing Grey Scale and Power Doppler information (GUIS-j/e). Results LDA was present in 33.7–65.0% at baseline and in 44.3–80.6% at follow-up, depending on the criteria used. MUDA-j/e was observed in 16.9% at baseline and in 30% at follow-up. GUIS-j/e was significantly higher in patients with moderate/high disease activity vs LDA according to DAPSA and PASDAS at baseline and DAPSA, PASDAS, Composite Psoriatic Disease Activity Index and minimal disease activity at follow-up. Patients in moderate/high disease activity had MUDA-j/e in 8.1–21.4% at baseline and in 8.3–20.0% at follow-up, depending on the applied clinical composite. MUDA-j/e patients with moderate/high disease activity had higher levels of pain and pain-related items than those with LDA. Conclusion The LDA cut-offs of DAPSA, PASDAS, Composite Psoriatic Disease Activity Index, minimal disease activity, but not DAS28-CRP are capable of distinguishing between high and low ultrasound activity. Pain and pain-related items are the main reason why PsA patients without signs of ultrasound inflammation are classified with higher disease activity.