what is mctd
Mixed Connective Tissue Disease. Mixed connective tissue disease (MCTD) is a rare autoimmune disorder featuring signs and symptoms of three different disorders: lupus, scleroderma and polymyositis.An autoimmune disorder is one in which the bodyâs immune system turns against the body it was designed to protect for unknown reasons.ixed Connective Tissue Disease. Mixed connective tissue disease (MCTD) is a rare autoimmune disorder featuring signs and symptoms of three different disorders: lupus, scleroderma and polymyositis.