Mixed connective tissue disease (MCTD) is a mixed manifestation of lupus erythematosus, dermatomyositis or polymyositis, scleroderma, rheumatoid arthritis, etc., and it is impossible to determine which disease it is. It is a connective tissue disease with high titers of spot-type fluorescent antinuclear antibodies and anti-nuclear glycoprotein (n-RNP) antibodies in the blood, with less kidney involvement, good response to corticosteroids, and good prognosis. This disease was first reported by Sharp et al. in 1972. There are different opinions on whether MCTD is an independent disease. Some people think it is a subtype of SLE, or propose that it is a subtype of PSS, but there are also many cases where the symptoms remain unchanged after years of observation and are considered to be an independent disease.