Mixed connective tissue disease (MCTD) is a systemic autoimmune disease that shares characteristics with at least two other systemic autoimmune diseases, including systemic sclerosis (Ssc), systemic lupus erythematosus (SLE), polymyositis/dermatomyositis (PM/DM), and rheumatoid arthritis.[2] The idea behind the "mixed" disease is that this specific autoantibody is also present in other autoimmune diseases such as systemic lupus erythematosus, polymyositis, scleroderma, etc. MCTD was characterized as an individual disease in 1972 by Sharp et al.,[3][4] and the term was introduced by Leroy[5] in 1980.[6]
Some experts consider MCTD to be the same as undifferentiated connective tissue disease,[7] but other experts specifically reject this idea[8] because undifferentiated connective tissue disease is not necessarily associated with serum antibodies directed against the U1-RNP. Furthermore, MCTD is associated with a more clearly defined set of signs and symptoms.[8]
^Sharp GC, Irvin WS, Tan EM, Gould RG, Holman HR (February 1972). "Mixed connective tissue disease--an apparently distinct rheumatic disease syndrome associated with a specific antibody to an extractable nuclear antigen (ENA)". The American Journal of Medicine. 52 (2): 148–59. doi:10.1016/0002-9343(72)90064-2. PMID4621694.