What is Muscular Dystrophy?
The muscular dystrophies (MD) are
a group of genetic diseases
characterized by progressive
weakness and degeneration of the
skeletal muscles that control
movement. There are many forms of
muscular dystrophy, some noticeable
at birth (congenital muscular
dystrophy), others in adolescence
(Becker MD), but the 3 most common
types are Duchenne,
facioscapulohumeral, and myotonic.
These three types differ in terms of
pattern of inheritance, age of
onset, rate of progression, and
distribution of weakness.
Duchenne MD primarily affects boys
and is the result of mutations in
the gene that regulates dystrophin -
a protein involved in maintaining
the integrity of muscle fiber. Onset
is between 3-5 years and progresses
rapidly. Most boys become unable to
walk at 12, and by 20 have to use a
respirator to breathe.
Facioscapulohumeral MD appears in
adolescence and causes progressive
weakness in facial muscles and
certain muscles in the arms and
legs. It progresses slowly and can
vary in symptoms from mild to
disabling.
Myotonic MD varies in the age of
onset and is characterized by
myotonia (prolonged muscle spasm) in
the fingers and facial muscles; a
floppy-footed, high-stepping gait;
cataracts; cardiac abnormalities;
and endocrine disturbances.
Individuals with myotonic MD have
long faces and drooping eyelids; men
have frontal baldness.
Is there any treatment?
There is no specific treatment
for any of the forms of MD.
Respiratory therapy, physical
therapy to prevent painful muscle
contractures, orthopedic appliances
used for support, and corrective
orthopedic surgery may be needed to
improve the quality of life in some
cases. Cardiac abnormalities may
require a pacemaker. Corticosteroids
such as prednisone can slow the rate
of muscle deterioration in patients
with Duchenne MD but causes side
effects. Myotonia is usually treated
with medications such as mexiletine,
phenytoin, or quinine.
What is the prognosis?
The prognosis of MD varies
according to the type of MD and the
progression of the disorder. Some
cases may be mild and progress very
slowly over a normal lifespan, while
other cases may have more marked
progression of muscle weakness,
functional disability, and loss of
the ability to walk. In Duchenne MD,
death usually occurs in the early
20s.
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