The diagnosis and classification of undifferentiated connective tissue diseases.

The term undifferentiated connective tissue disease (UCTD) refers to unclassifiable systemic autoimmune diseases which share clinical and serological manifestations with definite connective tissue diseases (CTDs) but not fulfilling any of the existing classification criteria. In this review we will go through the more recent evidence on UCTD and we will discuss in what extent the availability of new criteria for the CTDs could interfere with the "UCTD concept". The development of criteria able to identify early phases of defined CTD, may help in the differentiation of stable UCTD form their early stages and may offer a valuable guide to the treating physician to set up appropriate follow up schedules as well as therapeutic protocols. This simplified subset of CTD could offer a model to study clinic pathological correlations as well as the role of possible environmental factors in the development of autoimmunity.