Reactive arthritis (ReA) is a distinct subtype of spondyloarthritis with an abrupt onset and a propensity to progress to chronicity. Magnetic resonance imaging (MRI) has enabled the identification of sensitive indicators of therapeutic response. A longitudinal pilot study of acute ReA with knee joint involvement that met Braun’s criteria was conducted by the researchers. At the outset, magnetic resonance imaging of the knee was evaluated, as was in agreement with ultrasonography. A thorough and organized case record form was used to capture clinical details. Patients were followed up on, and MRI indicators of chronic arthritis transition were sought.

Synovial thickening was the most prevalent characteristic in 25 patients with ReA. On MRI, 20% of patients had enthesitis. ReA with urethritis and HLA-B27 positivity showed greater synovial thickening scores (P=0.007). The agreement between MRI and ultrasonography was low (synovial hypertrophy: k=0.04). At the 12-month follow-up, 34% (n=7/21 for >12 months) still had active disease. None of the clinical or radiological findings predicted chronicity.

B27 positivity and post urethritis on MRI, ReA was more severe than postenteritis ReA and RA. On follow-up, one-third acquire chronic illness. Although baseline imaging was not predictive of chronicity, magnetic resonance imaging was superior to sonography. The findings of the pilot exploratory investigation suggested that bigger studies on MRI in ReA were warranted.