Mixed Connective Tissue Disease

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Mixed connective tissue disease (MCTD) is a rare systemic autoimmune disease with an overlapping feature of at least two connective tissue diseases (CTD), including systemic lupus erythematosus (SLE), systemic sclerosis (SSc), polymyositis (PM), dermatomyositis (DM) and rheumatoid arthritis (RA) along with the presence of a distinctive antibody, anti-U1-ribonucleoprotein (RNP) previously known as antibody to extractable nuclear antigen (ENA). Most authors describe MCTD as an independent entity, while some believe that it might represent an early stage of a definite connective tissue disease, e.g., SLE, SSc, or overlap syndrome. MCTD has no unique clinical features, and there is a considerable inter-individual variation in clinical manifestations. Alarcon-Segovia is one of the regularly used diagnostic criteria that consists of high titer of positive anti-U1-RNP (over 1 per 1600) and three or more of the following clinical manifestations: Raynaud phenomenon, hand edema, synovitis, histologically proven myositis, and atherosclerosis. A revised set of diagnostic criteria for MCTD, which divides the features of the disease into the following four categories, was proposed by a consensus panel in Japan in 2019. These include Raynaud phenomenon Immunologic manifestation such as anti–U1-RNP antibody Organ involvement including pulmonary arterial hypertension, aseptic meningitis, trigeminal neuropathy Overlapping manifestations of SLE-like, systemic sclerosis, polymyositis, and dermatomyositis may present.