Interobserver Agreement in Magnetic Resonance of the Sacroiliac Joints in Patients with Spondyloarthritis.

Background. Clinical, laboratory, and radiologic parameters are used for diagnosis and classification of spondyloarthritis (SpA). Magnetic resonance imaging (MRI) of sacroiliac (SI) joints is being increasingly used to detect early sacroiliitis. We decided to evaluate the interobserver agreement in MRI findings of SI joints of SpA patients between a local radiologist, a rheumatologist, and an expert radiologist in musculoskeletal diseases. Methods. 66 MRI images of the SI joints of patients with established diagnosis of SpA were evaluated. Agreement was expressed in Cohen's kappa. Results. Interobserver agreement between a local radiologist and an expert radiologist was fair (κ = 0.37). Only acute findings showed a moderate agreement (κ = 0.45), while chronic findings revealed 76.5% of disagreement (κ = 0.31). A fair agreement was observed in acute findings (κ = 0.38) as well as chronic findings (κ = 0.38) between a local radiologist and a rheumatologist. There was a substantial agreement between an expert radiologist and a rheumatologist (κ = 0.73). In acute findings, a 100% agreement was achieved. Also chronic and acute plus chronic findings showed high levels of agreement (κ = 0.73 and 0.62, resp.). Conclusions. Our study shows that rheumatologists may have similar MRI interpretations of SI joints in SpA patients as an expert radiologist.