Impact of the new 2019 EULAR/ACR classification criteria for Systemic Lupus Erythematosus in a multicenter cohort study of 133 women with undifferentiated connective tissue disease.

OBJECTIVE We aimed to investigate the impact of applying the 2019 EULAR/ACR classification criteria for systemic lupus erythematosus (SLE) in a previously described cohort of women with undifferentiated connective tissue disease (UCTD). METHODS This study included 133 women with UCTD. At the time of inclusion into the study, none of the patients meet any classification criteria for other defined systemic connective tissue disease. RESULTS When applying the 2019 EULAR/ACR classification criteria to the cohort, 22 patients (17%) fulfilled the classification criteria of SLE. Patients classified as SLE had significantly higher frequency of mucocutaneous manifestations (23%vs.5%;p=0.007), arthritis (59%vs.17%; p<0.001), isolated urine abnormalities (18%vs.1%;p<0.001) and highly specific antibodies (50%vs.15%;p<0.001). At follow-up, these patients were statistically significantly more likely to fit also the ACR 1997 and SLICC criteria (18.2%vs. 1.8%;p<0.001). Patients who were diagnosed as SLE per the ACR 1997 and SLICC criteria during the follow-up scored significantly more points in the new 2019 EULAR/ACR classification criteria when compared to the other UCTD patients (mean score 8.3±3.7 vs. 4.5±4;p<0.05). CONCLUSION When applying the 2019 EULAR/ACR criteria for SLE in a cohort of patient with UCTD, we observed that in up to 17% of cases the original classification could be challenged. New implementation will help to early identify patients at higher risk of developing more severe CTD manifestations.