[Standardized diagnosis and treatment of undifferentiated connective tissue disease and mixed connective tissue disease].

Undifferentiated connective tissue disease (CTD) usually refers to patients who are presented with certain symptoms and signs related to CTD, and positive serological evidence of autoimmune diseases but don't fulfill any of the classification criteria for a certain CTD. Mixed CTD refers to patients who are presented with one or more clinical manifestations such as hand swelling, synovitis, myositis, Raynaud's phenomenon, and acrosclerosis. Patients with mixed CTD always have high-titer anti-nuclear antibodies (ANA) of speckled pattern and high-titer anti-U1 ribonuclear protein (RNP) antibody in serum, while with negative anti-Sm antibody. The update of diagnosis and treatment of undifferentiated CTD and mixed CTD lags behind other established CTD. There is a lack of evidence from randomized controlled trials or guidelines/recommendations on the treatment of undifferentiated CTD or mixed CTD. At present, the conventional therapy is mainly adopted according to the specific clinical manifestations of the disease. The standardized diagnosis and treatment of undifferentiated CTD and mixed CTD were drafted by the Chinese Rheumatology Association based on the previous guidelines and the progress of available evidence, so as to improve the management of these patients in China.