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Mixed Connective Tissue Disease
(MCTD)

Medical Author: William C. Shiel Jr., MD, FACP, FACR
Medical Editor: Dennis Lee, MD

MCTD vs. UCTD (Mixed Connective Tissue Disease vs. Undifferentiated Connective Tissue Disease)

Medical Author: William C. Shiel Jr., MD, FACP, FACR
Medical Editor: Melissa Conrad Stöppler, MD

Learn the difference between MCTD and UCTD.I note that some viewers have been requesting some clarification of the meaning of the terms "mixed connective tissue disease" (MCTD) and "undifferentiated connective tissue disease" (UCTD).

Connective tissue diseases are a special group of rheumatic diseases (diseases that feature abnormalities of the muscles and/or joints) that can be associated with arthritis. The cause(s) for the connective tissue diseases is (are) unknown. They are characterized as a group by the presence of spontaneous overactivity of the body's immune (defense) system. This overactivity results in the production of unusual antibodies that are found in the blood. The antibodies themselves may or may not cause any problems in patients with connective tissues diseases, but they are commonly found in the blood as a characteristic feature.

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 protein molecules, collagen and elastin. There are many different types of collagen protein that vary in amount in each of the body's tissues. Elastin has the capability of stretching and returning to its original length, like a spring or rubber band. Elastin is the major component of ligaments (tissues that attach bone to bone) and skin. In patients with connective tissue diseases, it is common for collagen and elastin to become injured by inflammation. Diseases in which inflammation of collagen tends to occur are also referred to as collagen diseases.

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 over activity of the immune system, which results in the production of unusual antibodies into 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.



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Mixed Connective Tissue Disease

What is a chest X-ray?

A chest X-ray is a radiology test that involves exposing the chest briefly to radiation to produce an image of the chest and the internal organs of the chest. An X-ray film is positioned against the body opposite the camera, which sends out a very small dose of a radiation beam. As the radiation penetrates the body, it is absorbed in varying amounts by different body tissues depending on the tissue's composition of air, water, blood, bone, or muscle. Bones, for example, absorb much of the X-ray radiation while lung tissue (which is filled with mostly air) absorbs very little, allowing most of the X-ray beam to pass through the lung.

What is a shadow on a chest X-ray?

Due to the differences in their composition (and, therefore, varying degrees of penetration of the X-ray beam), the lungs, heart, aorta, and bones of the chest each can be distinctly visualized on the chest X-ray. The X-ray film reco...

Read the Chest X-ray article »








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