Patterns of magnetic resonance imaging of the foot in rheumatoid arthritis: which joints are most frequently involved?

To investigate patterns of inflammatory MRI pathologies of the fore- and midfoot in rheumatoid arthritis (RA) and early RA (ERA) and their changes under therapy. In this prospective study, MRI data of the foot of 39 RA patients (29 female, 10 male; age: 54 ± 13 years; disease duration: 35 ± 37 months; baseline DAS28: 3.0 ± 2.0; medication: 29 DMARD, 1 biological, 9 symptomatic or non-specific treatment) were evaluated for synovitis in 314 joints, bone marrow edema and erosions according to RAMRIS criteria in a total of 585 joints. The change in joint pathology intensity was evaluated on follow-up MRI (time of follow-up: 8 ± 4 months) in 25 patients. Inflammation was generally more frequent in the metatarsophalangeal (MTP) joints (221/292; 76 %) than in the proximal metatarsal (47/292; 16 %) and tarsal bones (24/292; 8 %). The overall most frequently involved joints of the foot were MTP 5 (51/292; 18 %) and 1 (49/292; 17 %). Change under therapy was most frequently seen in the MTP 1 joint. Progress of inflammation in the MTP 1 was more frequently found in ERA patients than in patients with established RA (disease duration >12 months) (p = 0.002). In RA, the MTP joints, primarily MTP 5 and 1, are the predominant sites of inflammatory MRI pathologies of the foot. A change of inflammatory activity under therapy can be most frequently noted in the MTP 1 joint. This information might be helpful to improve effectiveness of MRI-controlled therapy approaches and clinical trials.