The diagnosis and classification of mixed connective tissue disease

The term “mixed connective tissue disease” (MCTD) concerns a systemic autoimmune disease typified by overlapping features between two or more systemic autoimmune diseases and the presence of antibodies against the U1 small nuclear ribonucleoprotein autoantigen (U1snRNP). Since the first description of this condition in 1972, the understanding of clinical manifestations and long-term outcome of MCTD have significantly advanced. Polyarthritis, Raynaud's phenomenon, puffy fingers, lung involvement and esophageal dysmotility are the most frequently reported symptoms among the different cohorts during the course of the disease. Moreover, in recent years a growing interest has been focused on severe organ involvement such as pulmonary arterial hypertension and interstitial lung disease which can accrue during the long-term follow-up and can still significantly influence disease prognosis. Over the last years, significant advances have been made also in disease pathogenesis understanding and a central pathogenetic role of anti-U1RNP autoantibodies has clearly emerged. Although controversies on disease definition and classification still persist, MCTD identifies a group of patients in whom increased surveillance for specific manifestations and prognostic stratification became mandatory to improve patient's outcomes.