Intermetatarsal bursitis is a new form of juxta-articular in
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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.

Researchers 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.

At the time of diagnosis, 157 early RA patients had a unilateral contrast-enhanced 1.5T forefoot MRI. The presence of IMB, as well as synovitis/tenosynovitis/osteitis, were assessed using the RA MRI scoring system (summed as RAMRIS-inflammation). In patients who had IMB at baseline and received early DMARD therapy, MRIs were assessed for IMB presence and size at 4/12/24 months. The researchers used logistic regression and generalised estimation equations. ACPA-strategization was carried out.

--69% of RA-patients had more than 1 IMB. In multivariable analysis on bursa-level, presence of IMB was independently associated with local presence of synovitis and tenosynovitis (OR 1.69 and 2.83 respectively), but not osteitis.

--On patient-level, IMB-presence was most strongly associated with tenosynovitis (2.92).

--IMB-presence associated with local joint-swelling (2.7) and tenderness (1.7) 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.

Finally, IMB is associated with inflammation of the synovial lining of joints and tendon sheaths, has a similar treatment response to DMARDs, and is associated with traditional clinical signs. These findings indicate that IMB is a common RA-feature of synovial inflammation in the juxta-articular region.