Analysis of the evolution to defined connective tissue diseases of patients with “early unidifferentiated connective tissue diseases (UCTD)”

The term undifferentiated connective tissue diseases (UCTD) is used to identify systemic autoimmune diseases not fulfilling classificative criteria for defined connective tissue diseases (CTD). Aim of the present study was to evaluate the evolution to defined CTD of an historical cohort of 91 UCTD patients followed at our Unit and to describe clinical and serological characteristics of stable UCTD patients with a disease duration of more than 5 years. Patients, previously described, were selected for having an undifferentiated profile after 1 year of follow up. These patients have been regularly followed at our Unit and their diagnosis has been reassessed annually based on the existing classificative criteria. Seven UCTD patients with a follow up of less than 5 years have been excluded from the study, therefore 84 patients (F: 81, M: 3) have been analysed. During the follow up 28 patients (33%) developed a defined CTD. In particular 22 patients developed systemic lupus erythematosus (SLE), while the remaining 6 patients developed other CTDs (2 primary Sjögren’s syndrome, 2 overlap syndromes, 1 Systemic Sclerosis, 1 rheumatoid arthritis). The evolution to a defined CTD occurred after a mean disease duration of 80.6± 66.8 months (min 14, max 336, median 72); the evolution to SLE occurred after a mean disease duration of 66.8±43.3 months (min 17, max 216, median 57). Anti-cardiolipin antibodies were the only variable correlated with the evolution to SLE (p<0.05). Stable UCTD were characterized by a simplified clinical picture with no major organ involvement and by a simplified autoantibody profile (anti-Ro/SSA antibodies and anti-RNP antibodies were the single antibody specificities observed in 22% and 13% of patients respectively). These results confirm previous data showing that about 30% of UCTD patients will develop a defined CTD, the predictive role of anti-cardiolipin antibodies for the evolution to SLE, and the existence of stable UCTD, distinct clinical entities with a simplified clinico-serological profile. The early identification of stable UCTD is very important both from a clinical and a research point of view. Future research is needed to define a new set of classification criteria.