Achilles tendon enthesitis evaluated by MRI assessments in patients with axial spondyloarthritis and psoriatic arthritis: a report of the methodology of the ACHILLES trial

Abstract Background The currently available scoring methods for enthesitis are often measures of pain but not of inflammation at entheseal sites. The Outcome Measures in Rheumatology Clinical Trials (OMERACT) psoriatic arthritis (PsA) magnetic resonance imaging (MRI) scoring system (PsAMRIS) assesses inflammation and damage in PsA and was particularly developed for the hands. The ACHILLES trial used clinical measures for heel enthesitis in combination with MRI scoring based on PsAMRIS. Methods Patients (age ≥ 18 years) with spondyloarthritis (SpA) and PsA were included in the trial if they presented with clinical and MRI-positive heel enthesitis. MRI of the affected heel was performed at three time points: screening, Week 24 and Week 52. Inflammatory MRI findings (tendinitis, bursitis and bone marrow oedema [BME]) in the area of the Achilles tendon and/or plantar aponeurosis, periarticular inflammation of the ankle joint and heel erosion were assessed qualitatively (absent/present). In addition, BME and bone erosion were quantitatively assessed based on PsAMRIS, where their proportion was compared to the volume of the affected bone. Mean scores of BME and bone erosion quantification were calculated, and the mean composite score (based on PsAMRIS) was calculated based on the individual score of each subject for periarticular inflammation, BME and bone erosion and further extended for bursitis and tendinitis. Modifications to PsAMRIS were introduced by categorising oedema length as ≤/> 0.5 cm and locating bone erosion. Conclusions In ACHILLES, MRI was used to assess and evaluate heel enthesitis. Due to the lack of a validated scoring system for heel enthesitis at the time of ACHILLES initiation, this trial applied quantitative scoring based on PsAMRIS, with specific adaptations for the heel. Trial registration National Clinical Trial Registry, NCT02771210 . Registered 13 May 2016.