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
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.
Next: What is mixed connective tissue disease? »


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