Application of SLICC classification criteria in undifferentiated connective tissue disease and evolution in systemic lupus erythematosus: analysis of a large monocentric cohort with a long-term follow-up.

Objectives The objectives of this study were to analyse the performance of the Systemic Lupus International Collaborating Clinics (SLICC) 2012 classification criteria for systemic lupus erythematosus (SLE) in a large cohort of undifferentiated connective tissue disease (UCTD) population at onset of the disease and during a long-term follow-up of 15 years (1999-2013) and to evaluate the transition from UCTD to SLE, according to American College of Rheumatology (ACR) 1997 and SLICC 2012 classification criteria. Methods A cohort of patients who met the classification criteria proposed by Mosca et al. for UCTD, were analysed. The SLICC 2012 classification criteria for SLE were retrospectively applied to each patient at the time of the diagnosis (T0) and also periodically re-applied and compared to ACR 1997 criteria at three different time points in the follow-up. Results 329 patients were enrolled. According to inclusion criteria at T0 no patient met the SLE/ACR criteria, whilst, retrospectively applying the SLE/SLICC criteria, 44 patients already satisfied this set of criteria for SLE. During the follow-up 23 new patients reached the SLE/SLICC criteria and 14 patients met the ACR criteria with a stable rate of progression to SLE over time. Acute or subacute skin rash, antiphospholipid antibody (aPL) positivity and serositis were the variables correlated to the evolution to SLE. Conclusions In our UCTD population, the application of SLICC classification criteria for SLE at disease onset allowed identification of a proportion of otherwise missed SLE cases; during follow-up, and compared with ACR criteria, SLICC criteria expanded the number of patients classifiable as SLE otherwise classified as UCTD.