This study was undertaken to assess the inflammatory burden in peripheral spondyloarthritis (SpA) by magnetic resonance imaging (MRI) of the legs in an early remission-induction strategy study of tumor necrosis factor (TNF) blockade. Furthermore, we sought to determine the value of MRI to predict disease relapse versus sustained remission after treatment discontinuation.
Thirty-two patients with early peripheral SpA with involvement of the legs determined on clinical examination and confirmed by ultrasonography (US) participated in a remission-induction trial of a TNF inhibitor (TNFi). Patients underwent MRI of the joints and entheses of the legs at baseline and at clinical remission, after which TNFi treatment was withdrawn. Images were evaluated for joint effusion, joint osteitis, entheseal soft tissue inflammation, and entheseal osteitis.
Joint effusion and enthesitis on clinical examination and US correlated well with MRI abnormalities. In addition, a substantial amount of subclinical involvement was seen on MRI, mainly in the ankle joints and heel entheses. Inflammation scores were markedly lower in the subclinically involved joints and entheses versus those that were clinically involved (P values ranged from 0.01 to <0.001). Inflammatory load on MRI decreased significantly upon TNFi treatment (P < 0.001). Whereas 80% of the joints that were clinically involved at baseline showed no effusion on remission MRI, 2 of 3 entheses involved at baseline showed residual inflammation. In addition, patients who experienced a relapse after treatment discontinuation displayed more entheseal soft tissue inflammation on remission MRI compared to those who maintained drug-free remission (P = 0.028).
Our findings delineate a differential response of synovitis and enthesitis, with enthesitis on MRI being less responsive to TNFi treatment. Furthermore, residual entheseal inflammation might be indicative of the need for continuous therapy.