Mixed connective tissue disease has features of lupus, systemic sclerosis, and polymyositis. Diagnosis of mixed connective tissue disease is based primarily on the presence of abnormal antibodies in the blood. Treatment is usually with corticosteroids, but side effects must be noted.

Mixed connective tissue disease is an autoimmune disease that occurs most commonly in young and middle-aged women. It is characterized by symptoms of damage to multiple organs, with clinical features of several different autoimmune diseases.

Connective tissue diseases are disorders that involve protein-rich tissues. Examples include fat, bone, and cartilage. These disorders often involve joints, muscles, and skin. There are more than 200 different disorders that can affect connective tissue. The specific causes and symptoms vary depending on the disorder.