CHARACTERISTIC MAGNETIC-RESONANCE-IMAGING ENTHESEAL CHANGES OF KNEE SYNOVITIS IN SPONDYLARTHROPATHY

Objective. To use magnetic resonance imaging (MRI) in patients with rh eumatoid arthritis (Ri) and spondylarthropathy (SpA) to determine if t he primary site of abnormality differs. Methods. Twenty patients with recent-onset knee effusion (10 with SpA and 10 with RA) were evaluated using fat-suppressed MRI. Knee joint effusion and synovitis were conf irmed using ultrasonography. MRI scans were independently scored by 2 observers who were blinded to the patient's diagnosis, Results. All 10 of the SPA patients, but only I of the 10 Ri patients, had focal peri -entheseal high signal (compatible with fluid or edema) outside the jo int (P = 0.01). Six of the SpA patients had bone marrow edema that was maximal at entheseal insertions; in 4 cases this was multifocal, No R A patients showed such an abnormality (P = 0.01), Conclusion. Prominen t entheseal abnormalities on MRI are a consistent feature of new-onset synovitis in SpA, but are a minor feature of RA. This finding has imp ortant implications for the diagnosis, classification, and mechanisms of synovitis in patients with SpA.