Intermetatarsal bursae in the forefeet possess a synovial lining, similarly to joints and tendon-sheaths. Inflammation of these bursae (intermetatarsal bursitis; IMB) was recently identified as specific for early RA. We hypothesised that if IMB is indeed an RA-feature, then it associates with 1) other local inflammatory measures (synovitis/tenosynovitis/osteitis), 2) clinical signs and 3) responds to DMARD-therapy similarly as other local inflammatory measures.
157 consecutive early RA-patients underwent unilateral contrast-enhanced 1.5T forefoot-MRI at diagnosis. MRIs were evaluated for IMB-presence, and for synovitis/tenosynovitis/osteitis in line with the RA MRI scoring-system (summed as RAMRIS-inflammation). MRIs at 4/12/24 months were evaluated for IMB-presence and -size in patients who had IMB at baseline and received early DMARD-therapy. Logistic regression and generalised estimating equations were used. ACPA-stratification was performed.
69% of RA-patients had ≥1 IMB. In multivariable analysis on bursa-level, presence of IMB was independently associated with local presence of synovitis and tenosynovitis (OR 1.69(95%CI 1.12-2.57) and 2.83(1.80-4.44), respectively), but not osteitis. On patient-level, IMB-presence was most strongly associated with tenosynovitis (2.92(1.62-5.24)). IMB-presence associated with local joint-swelling (2.7(1.3-5.3)) and tenderness (1.7(1.04-2.9)) independent of RAMRIS-inflammation. During treatment, IMB-size decreased between 0-12 months. This decrease associated with decrease in RAMRIS-inflammation; which was driven by synovitis-decrease. Within ACPA-positive and ACPA-negative RA similar results were obtained.
IMB particularly accompanies inflammation of the synovial lining of joints and tendon-sheaths, showed a similar treatment response after DMARD-initiation and associates with typical clinical signs. These findings suggest that IMB represents a frequently present novel RA-feature of juxta-articular synovial inflammation.