The performances of the ILAR, ASAS, and PRINTO classification criteria in ERA patients: a comparison study

Enthesitis-related arthritis (ERA) could be considered the pediatric equivalent of ankylosing spondylitis in adults albeit with certain significant differences. We aim to evaluate the sensitivity and specificity of the International League of Associations for Rheumatology (ILAR), the Assessment of Spondyloarthritis International Society (ASAS), and the preliminary Pediatric Rheumatology International Trials Organization (PRINTO) classification criteria in ERA patients.

The medical records of ERA patients who were followed up between January 2005 and September 2020 have been analyzed. The control group consisted of patients with oligoarticular JIA (n = 146), polyarticular JIA (n = 55), and psoriatic arthritis (n = 20).

This retrospective study included 108 ERA (73.1% male) and 221 control patients (25.8% male). The median age at diagnosis for ERA and control patients were 12.5 and 4.0 years, respectively (p < 0.001). Arthritis was observed more frequently in the control group at diagnosis and in the follow-up (p < 0.001 for both), while enthesitis, sacroiliac joint tenderness, and inflammatory back pain were more common in the ERA group both at diagnosis and in the follow-up (p < 0.001 for all). In sacroiliac imaging, 70.1% of ERA patients had positive findings suggestive of sacroiliitis at diagnosis and 78% in the follow-up. The sensitivities of ILAR, PRINTO, ASAS criteria for axial SpA, and peripheral SpA at diagnosis were 74.0%, 57.4%, 21.3%, and 85.1%, respectively which increased to 82.4%, 78.7%, 35.1%, and 92.5%, respectively at follow-up. The specificities were 100%, 100%, 99.1%, and 90.9%, respectively at both diagnosis and follow-up.

The ASAS criteria for peripheral SpA were the most sensitive while ILAR and the preliminary PRINTO criteria were the most specific criteria for classifying ERA patients.

The ASAS criteria for peripheral SpA were the most sensitive criteria for classifying ERA patients. The use of ASAS axial SpA criteria may provide early detection of axial involvement.