Mixed connective tissue disease (MCTD) is an autoimmune disease in which the immune system produces antibodies that attack the body's own healthy cells. (The immune system misidentifies normal bodily tissues as if they were dangerous, external agents like viruses or bacteria.) It is rare in children. Patients with MCTD can have features of multiple autoimmune diseases. For example:
To be diagnosed with MCTD, however, a person must test positive for the anti-RNP (ribonucleic protein) antibody, in addition to meeting specific clinical criteria. Patients who have signs and symptoms of multiple autoimmune diseases but who do not test a positive for anti-RNP antibody are diagnosed as having what is called an "overlap syndrome." (Rheumatologists and scientists do not all agree on a precise definition for "overlap syndrome." In general, this term refers to a condition in which a patient has symptoms of two or more recognized autoimmune diseases.)
As with other connective tissue diseases, the symptoms of MCTD can range from very mild to life-threatening. Often, patients with MCTD have systemic symptoms such as fevers, weight loss, a decrease in energy, and feelings of weakness. The most common symptoms at diagnosis include Raynaud’s phenomenon (temporary changes in the colors of the fingers and toes caused by stress or exposure to cold) and arthritis (warmth, swelling, tenderness and limitation of motion of a joint). It is important to understand that all of these symptoms can indicators of other conditions. Some patients with MCTD will have additional symptoms that affect body organs such as the lungs, heart and skin.
Diagnosis is based on symptoms, physical exam findings, lab tests and radiological imaging studies. Since patients will show signs and symptoms of multiple disorders, MCTD and overlap syndrome are both difficult to diagnose. Sometimes it may take months or even years to determine the correct diagnosis, as symptoms tend to evolve over time. A positive test for anti-RNP antibody is required to make diagnosis of MCTD. Patients who test negative for this antibody are diagnosed as having overlap syndrome. In addition to this testing, blood and urine, cardiac and pulmonary studies are frequently monitored.
The treatment of MCTD focuses on suppressing the immune system and alleviating the specific symptoms of each individual patient. Raynaud’s phenomenon can be managed by avoiding cold exposure and wearing warm clothing. Sometimes, medications that target the blood vessels are necessary to help increase blood flow to the hands and toes. Many patients require steroids and other oral, subcutaneous or intravenous (IV) immunosuppressive drugs to manage the symptoms of this disease.