Residual inflammation in psoriatic arthritis patients in stable minimal disease activity.

Background: In psoriatic arthritis (PsA), low disease activity as defined by the Minimal Disease Activity (MDA) index is considered a good treatment target. However, as MDA is based only on clinical findings, it might not capture pauci-symptomatic inflammation. Sensitive imaging such as ultrasound (US) might disclose residual inflammatory signs in PsA patients in MDA. Methods: In this cross-sectional multicentre study, adult PsA patients on biologic treatment in MDA for at least 6 months were consecutively enrolled for a thorough clinical and US examination. Data collection included demographics, personal history, main patient's reported outcomes, clinical and US findings of joints, tendon sheaths, tendons, bursae, and entheses involvement. All centers performed the US investigation in B-mode and Power Doppler (PD)-mode using a similar US machine equipped with a 18-6 and 13-5 MHz multifrequency linear probe. Statistical analysis included comparisons between groups and correlation tests. Results: The 72 PsA patients enrolled in the study had a median duration of MDA of 12 (6-65) months. Overall, US examination revealed a low number of acute lesions. However, 54% of patients had at least one PD signal in the examined tissues. A joint or enthesis positive PD signal was found in about 19 and 24% of patients, respectively. Synovial hypertrophy, at least one acute entheseal lesions, and bursitis were the most common changes, detected in 41.7, 41.7 and 26% of patients, respectively. Conclusions: PsA patients in a stable state of MDA may still have residual inflammation in peripheral articular structures detectable by US examination.