Objectives To investigate the ability of whole-body MRI (WBMRI) to detect axial and peripheral enthesitis in patients with psoriatic arthritis (PsA) and axial spondyloarthritis (axSpA), and in healthy subjects (HS). Furthermore, to develop MRI enthesitis indices based on WBMRI and validate these by use of clinical measures of disease activity.

Methods Prospective cross-sectional study of patients with PsA (n=18) and axSpA (n=18) with moderate to high disease activity, and HS (n=12). Enthesitis at 35 individual sites located at upper and lower limbs, chest and pelvis were evaluated by WBMRI and clinical examination, and compared. Three new WBMRI enthesitis indices were developed.

Results WBMRI allowed evaluation of 888 (53%) of 1680 sites investigated, and 19 (54%) of 35 entheses had a readability >70%. The percentage agreement between WBMRI and clinical enthesitis was 49–100%, when compared at the level of the individual entheses. Enthesitis on WBMRI was observed in 148 (17%) of the entheseal sites, and was frequently present at greater trochanters (55%) and Achilles (43%) and supraspinate (23%) tendon insertions in patients and HS. At the first mentioned two locations enthesitis often appeared without clinical signs of enthesitis. Patients and HS differed significantly in one of the new WBMRI enthesitis scores. Patients and HS differed significantly in one of the new WBMRI enthesitis scores, and this score correlated weakly with BASDAI question 4 (tenderness in relation to entheses), BASDAI and patient global (ρ=0.29–0.31, p<0.05).

Conclusions WBMRI is a promising new imaging modality for evaluation of enthesitis in patients with PsA and axSpA, but requires further investigation before clinical use.