Applying SLICC and ACR/EULAR systemic lupus erythematosus classification criteria in a cohort of patients with undifferentiated connective tissue disease

Background/objective: New classification criteria for SLE have recently been developed. How these criteria affect the classification of patients with the SLE-mimicking condition UCTD is poorly understood. This study investigated the reclassification of UCTD patients using newly derived SLE criteria. Methods: Patients with UCTD were identified within a single academic medical center using ICD9/10 codes. Medical record review was performed to confirm UCTD diagnosis and identify disease features present at diagnosis. The SLICC and ACR/EULAR criteria were applied, after which we compared the proportion of patients reclassified as SLE and determined which disease features were associated with reclassification. Results: A total of 129 patients were included in the study. When applying the SLICC and ACR/EULAR criteria, 18 (14.0%) and 26 patients (20.2%) were reclassified as SLE. Comparison with McNemar’s test trended toward statistical significance (p = 0.057). Cohen’s kappa coefficient was 0.62 (p < 0.001), indicating substantial agreement between these criteria. Disease features associated with reclassification as SLE were renal involvement, leukopenia, thrombocytopenia, anti- dsDNA antibody, hypocomplementemia, non-scarring alopecia (SLICC), and arthritis (ACR/EULAR). Conclusions: Both the SLICC and ACR/EULAR criteria exhibit increased SLE classification. These newer classification criteria could be used to increase the number of SLE patients in future clinical studies.