Conditions characterized by the presence of clinical and serological manifestations suggestive of systemic autoimmune diseases but not fulfilling the classification criteria for defined connective tissue disease (CTD) are common in clinical practice and are indicated as undifferentiated (U) CTDs. Although epidemiological data are not available in the literature, up to 50% of the patients with an undifferentiated CTD of less than one year of duration were reported. The majority of patients suffering from UCTDs are young females, do not evolve into full blown CTD and are stable over time displaying mild clinical manifestations and single autoantibody profile. The early identification of stable UCTD is important for therapeutic and prognostic reasons and for investigating the pathogenic significance of autoantibodies or the role of the genetic background. Classification criteria for stable UCTDs are still matter of debate.
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