Connective tissue disease is a group of diseases with myxoid edema and fibrinoid degeneration of loose connective tissue as pathological basis. It was first believed that it was mainly caused by fibrinoid degeneration of collagen fibers, so it was called diffuse collagen disease or collagen vascular disease. Later, it was believed that the main lesions were not limited to collagen fibers, and it was renamed connective tissue disease. The cause is not very clear, and it is generally believed to be related to genetics, immunity, and viral infection, and it is a multi-factorial disease. With the progress of immunology, it has been found that most connective tissue diseases are accompanied by immunological abnormalities, such as low function of inhibitory T cells and hyperfunction of humoral immunity. Some connective tissue diseases have autoantibodies, so this group of diseases is also classified as immune diseases or autoimmune diseases.