Ultrasound imaging for the rheumatologist XXVIII. Impact of sonographic knee joint involvement in recent-onset inflammatory polyarthritis

Objective. To assess the impact of the knee joint inflammation, detected by ultrasonography (US), on functional disability in patients with recent-onset inflammatory polyarthritis (IP). Methods. We included patients who had IP for less than 12 months and who had more than 5 swollen joints. All patients were assessed clinically at baseline. US was used to identify joint inflammation at multiple joint sites including: hands, wrists, elbows, shoulders, knees, ankles and feet. Joint group involvement was defined when at least one joint showed intra-articular signs of inflammation (synovial fluid abnormalities and/or synovial hypertrophy), according to the OMERACT definitions. Functional disability was measured using the health assessment questionnaire (HAQ) score. All patients with complete clinical and US data were included in the analysis. Results. Patients with US knee involvement showed more active and severe disease at baseline. The mean difference of HAQ between patients with and without US knee inflammation was 0.42 (95%CI 0.22, 0.62; p<0.001). This difference was still clinically and statistically significant even after controlling for disease extension and pattern of joint involvement. US shoulder involvement was also significantly and independently associated with higher mean HAQ scores. Conclusion. US knee involvement is associated with higher disability in IP at first presentation. US is a good tool to help in the differentiation of patients with recent-onset IP with different disease severity.