Mixed connective tissue disease is a term used by some doctors to describe a disorder characterized by features of systemic lupus erythematosus, systemic sclerosis, and polymyositis.
About 80% of people who have this disease are women. Mixed connective tissue disease occurs worldwide and affects people aged 5 to 80, often peaking in incidence during adolescence and in the 20s. Its cause is unknown, but it seems to be an autoimmune disorder.
The typical symptoms are Raynaud phenomenon (in which the fingers suddenly become very pale and tingle or become numb or blue in response to cold or emotional upset—see see Raynaud's Syndrome), joint inflammation (arthritis), swollen hands, muscle weakness, difficulty swallowing, heartburn, and shortness of breath. Raynaud phenomenon may precede other symptoms by many years. Regardless of how mixed connective tissue disease starts, it tends to worsen, and symptoms spread to several parts of the body.
Lupuslike rashes may develop. Skin changes similar to those of systemic sclerosis also may occur, such as tightening of the finger skin. The hair may thin.
Almost everyone with mixed connective tissue disease has aching joints. About 75% of people develop the swelling and pain typical of arthritis. Mixed connective tissue disease damages the muscle fibers, so the muscles may feel weak and sore, especially in the shoulders and hips. Tasks such as lifting the arms above the shoulders, climbing stairs, and getting out of a chair can become very difficult.
The lungs are affected in up to 75% of people with mixed connective tissue disease. Fluid may collect in or around the lungs. In some people, abnormal lung function is the most serious problem, causing shortness of breath during exertion.
Occasionally, the heart is weakened, leading to heart failure (see see Heart Failure). Symptoms of heart failure may include fluid retention, shortness of breath, and fatigue. The kidneys are affected in about 25% of people, and the damage is usually mild compared to the damage caused by lupus. Other symptoms may include fever, swollen lymph nodes, and abdominal pain. Sjögren syndrome (see Sjögren Syndrome) may develop. Over time, most people develop symptoms that are more typical of lupus (see Systemic Lupus Erythematosus (SLE)) or systemic sclerosis (see Systemic Sclerosis).
Doctors suspect mixed connective tissue disease when symptoms of lupus, systemic sclerosis, and polymyositis (see Polymyositis) overlap.
Blood tests are done to detect an antibody to ribonucleoprotein, which is present in most people who have mixed connective tissue disease. A high level of this antibody without the other antibodies present in other similar disorders is characteristic of mixed connective tissue disease.
If doctors suspect certain organs are affected, they may do other tests, such as magnetic resonance imaging (MRI) or a muscle biopsy (removal of a piece of muscle tissue for examination and testing), to detect problems.
Despite treatment, mixed connective tissue disease worsens in about 13% of the people, causing potentially fatal complications in 6 to 12 years. The prognosis is worse for people who have mainly features of systemic sclerosis or polymyositis. Overall, 80% of people survive at least 10 years after the diagnosis is made. Symptom-free periods can last for many years with no treatment.
The treatment is similar to that of lupus. Corticosteroids are usually effective, especially when the disease is diagnosed early. Mild cases can be treated with nonsteroidal anti-inflammatory drugs (NSAIDs), hydroxychloroquine or similar drugs, or very low doses of corticosteroids. The more severe the disease, the higher the dose of corticosteroid needed. In severe cases, immunosuppressive drugs (such as azathioprine, methotrexate, or cyclophosphamide) may also be needed.
In general, the more advanced the disease and the greater the organ damage, the less effective the treatment. Systemic sclerosis–like damage to the skin and esophagus is least likely to respond to treatment.
People who take corticosteroids are at risk of fractures related to osteoporosis. To prevent osteoporosis, these people are given the drugs used to treat osteoporosis, such as bisphosphonates and supplemental vitamin D and calcium. People who have mixed connective tissue disease are at increased risk of atherosclerosis (see Atherosclerosis) and are closely monitored by doctors. People who are receiving immunosuppressants are also given drugs to prevent infections such as by Pneumocystis jirovecii.
Last full review/revision August 2013 by Rula A. Hajj-ali, MD