Adult-onset Still's disease (AOSD) is an adult form of systemic juvenile idiopathic arthritis (JIA) that differs from the latter in its classification. This study evaluated the concordance between the International League Against Rheumatism (ILAR) criteria for systemic JIA and the Yamaguchi criteria and then compared their possible prognostic value in patients with AOSD.
In a retrospective review of 169 adults with suspected AOSD, patients were classified according to the Yamaguchi or ILAR criteria. Then the concordance in cross-referencing the other group with the different criteria was investigated and the sensitivity and specificity of each set of criteria were determined. Disease activity markers in AOSD patients were correlated with positivity according to both systems.
Concordance was good in patients with suspected AOSD (k = 0.7144, p <  0.001) and low in those with a diagnosis of AOSD (k = 0.3787, p <  0.001). The sensitivity of the ILAR criteria in AOSD patients was 0.8864 (95% confidence interval (CI): 0.8322-0.9405), and the specificity was 0.7838 (0.6511, 0.9164). Positivity according to the ILAR criteria correlated with the systemic score (r = 0.763, p <  0.0001) and C-reactive protein levels (r = 0.183, p = 0.0356) and was associated with a relapse (odds ratio: 1.589, 95% CI: 1.043-2.421), macrophage activation syndrome (MAS; odds ratio: 1.993, 95% CI: 1.218-3.263) and care in the intensive care unit (ICU; odds ratio: 2.087, 95% CI: 1.086-4.011).
In AOSD patients, there is fair concordance between the Yamaguchi and ILAR criteria for systemic JIA. Positive ILAR criteria may be useful for identifying AOSD patients at high risk for relapse, MAS and the need for ICU care. Further studies including larger populations from several centers are needed to confirm our results regarding the utility of the ILAR criteria in AOSD patients.