Mixed connective tissue disease facts
- Connective tissues are the framework of the cells of the body.
- Mixed connective tissue disease is an "overlap" combination of connective tissue diseases.
- Diagnosis of mixed connective tissue disease is supported by detecting abnormal antibodies in the blood.
- Treatment of mixed connective tissue disease is directed at suppressing immune-related inflammation of tissues.
What are connective tissues?
The connective tissues are the structural portions of our body that essentially hold the cells of the body together. These tissues form a framework or matrix for the body. The connective tissues are composed of two major structural molecules, collagen and elastin. There are many different collagen proteins that vary in amount in each tissue of the body. Elastin is another protein that has the capability of stretching and returning to original length like a spring. Elastin is the major component of ligaments (tissues which attach bone to bone).
Connective tissue diseases are disorders featuring abnormalities involving the collagen and elastin. Connective tissue diseases are often characterized by a variety of immune abnormalities that are common for each particular type of illness.
What diseases characteristically affect connective tissue?
Diseases of connective tissue that are strictly inheritable (due to genetic inheritance) include Marfan syndrome (can have tissue abnormalities in the heart, aorta, lungs, eyes, and skeleton) and Ehlers-Danlos syndrome (may have loose, fragile skin or loose [hyperextensible] joints). Pseudoxanthoma elasticum is an inherited disorder of elastin.
Other diseases of connective tissue do not have specific gene abnormalities as their sole cause. These connective tissue diseases occur for unknown reasons. They are characterized as a group by the presence of spontaneous overactivity of the immune system, which results in the production of unusual antibodies in the blood.
The classic immune-related connective tissue diseases include systemic lupus erythematosus, rheumatoid arthritis, scleroderma, polymyositis, and dermatomyositis. Each of these diseases has a characteristic presentation with typical clinical findings that doctors can recognize during an examination. Each also has characteristic blood test abnormalities and abnormal antibody patterns. However, each of these diseases can evolve slowly or rapidly from very subtle abnormalities before demonstrating the classic features that help in the diagnosis. When these conditions have not developed the classic features of a particular disease, doctors will often refer to the condition as "undifferentiated connective tissue disease." This implies that the characteristic features that are used to define the classic connective tissue disease are not present, but some symptoms or signs of connective disease exist. Individuals with undifferentiated connective tissue disease may never develop a fully definable condition or they may eventually develop a classic connective tissue disease.
What is mixed connective tissue disease?
Mixed connective tissue disease, as first described in 1972, is "classically" considered as an "overlap" of three diseases, systemic lupus erythematosus, scleroderma, and polymyositis. Patients with this pattern illness have features of each of these three diseases. They also typically have very high quantities of antinuclear antibodies (ANAs) and antibodies to ribonucleoprotein (anti-RNP) detectable in their blood. The symptoms of many of these patients eventually evolve to become dominated by features of one of three component illnesses, most commonly scleroderma. Mixed connective tissue disease is often abbreviated MCTD.
It is now known that overlap syndromes can occur that involve any combination of the connective tissue diseases. Therefore, for example, patients can have a combination of rheumatoid arthritis and systemic lupus erythematosus (hence, the coined name "rhupus").