Muscular
Dystrophy
What
is it?
Muscular dystrophy is the
term used to describe a group of inherited
disorders that cause progressive muscle weakness.
There are nine types of muscular
dystrophies, listed here in alphabetical order.
Becker
muscular dystrophy (BMD):
Affects older boys and young men. Causes
progressive muscle weakness, usually beginning in
the legs. It
is similar to Duchenne muscular dystrophy, but is
generally milder.
Congenital
muscular dystrophy (CMD):
A rare form present from birth.
Symptoms usually progress slowly and
include general weakness, flaccid tone, bent
joints, and slow motor development.
Fukuyama CMD is another type of congenital
CMD that usually involves mental retardation, and
is more common in Japan.
Distal
muscular dystrophy (DD):
Symptoms begin in middle age or later.
Causes weakness in the muscles of the feet
and hands.
Duchenne
muscular dystrophy (DMD):
The most severe form.
Affects young boys.
Causes progressive muscle weakness, usually
beginning in the legs.
Emery-Dreifuss
muscular dystrophy (EDMD):
Affects young boys.
Causes muscle contractions in the calves;
weakness in the calves, shoulders, and upper arms;
and problems in the way electrical impulses travel
through the heart to make it beat.
Facioscapulohumeral
muscular dystrophy (FSH):
Also known as Landouzy-Dejerine disease.
Begins in late childhood to early
adulthood.
Affects both males and females.
Causes weakness in the muscles of the face,
shoulders, and upper arms.
May also affect the hips and legs.
Limb-girdle
muscular dystrophy (LGMD):
Begins in late childhood to early
adulthood. Affects
males and females.
Causes weakness in the muscles around the
upper legs and shoulders.
Myotonic dystrophy:
Also known as Steinert's disease. Symptoms
may begin any time from birth through adulthood.
Affects males and females.
Generalized weakness first occurs in the
face, hands, and feet.
People with this disease also have myotonia,
the failure of the muscles to relax normally after
use.
Oculopharyngeal
muscular dystrophy (OPMD):
Affects adults of both sexes.
Causes weakness in the eye muscles and
throat.
Who
gets it?
BMD
occurs in about 1 in 30,000 male births. Both CMD
and Fukuyama CMD are rare.
DD
is most common in Sweden, and rare in other parts
of the world.
DMD
occurs in about 1 in 3,500 male births, and
affects approximately 8,000 boys and young men in
the United States. A milder form occurs in a very
few female carriers.
Fewer than 300 cases of
EDMD have been identified. FSH
occurs in about 1 out of every 20,000 people, and
affects approximately 13,000 people in the United
States. The
number of people with LGMD
is difficult to estimate, but may be in the low
thousands in the United States.
Myotonic
dystrophy is the most common form of muscular
dystrophy, affecting more than 30,000 people in
the United States.
OPMD is most common among French Canadian families in Quebec, and in
Spanish-American families in the southwestern
United States.
What
causes it?
The muscular dystrophies are
caused by genetic defects, which means they are
inherited at birth. While the affected genes have
been identified for some forms of muscular
dystrophy, such as DMD, BMD, CMD, and most forms
of LGMD, the genes responsible for the other forms
have not yet been identified.
What
are the symptoms?
Muscle weakness is the common
major symptom of all types of muscular
dystrophies.
However, the location of symptoms, age at
which they begin, and how they progress vary.
Symptoms for specific types are listed here
in alphabetical order.
Becker
muscular dystrophy (BMD):
Symptoms are similar to DMD, but usually
milder. Patients
with BMD often can walk independently into their
twenties or early thirties because the same
pattern of leg weakness, unsteadiness, and
permanent muscle tightening (contractures) occurs
later with BMD.
Symptoms may also include mild and slowly
progressing scoliosis, heart muscle disease (cardiomyopathy),
irregular heartbeats (arrhythmias), congestive
heart failure, fatigue, shortness of breath, chest
pain, and dizziness.
Eventually, patients may need a ventilator
to help with breathing because of respiratory
weakness.
Congenital
muscular dystrophy (CMD):
Infants with CMD have severe muscle
weakness from birth, with very little muscle tone
and voluntary movement.
Children with CMD, however, can eventually
learn to walk, with or without the aid of an
assisting device.
CMD patients can live into young adulthood
or beyond. Children
with Fukuyama CMD are rarely able to walk, and
have severe mental retardation.
Most children with this type of CMD die in
childhood.
Distal
muscular dystrophy (DD):
Symptoms include weakness in the hands,
forearms, and lower legs. At first, patients may
notice difficulty with activities involve fine
motor skills, such as tying shoes or fastening
buttons. Symptoms
progress slowly, and the disease usually does not
affect life span.
Duchenne
muscular dystrophy (DMD):
Symptoms begin to show in pre-school boys.
First, the legs are affected, causing walking
difficulties and balance problems.
As the disease progresses, the calves begin
to swell
with fibrous tissue rather than with muscle, and feel firm
and rubbery.
For this reason, DMD
is also known as pseudohypertrophic
muscular dystrophy.
By age five or six, the child will have
contractures (permanent muscle tightening), mostly
in the calf muscles. This tightening pulls the
foot down and back, so the child must walk on
tip-toes. By age nine or ten, it becomes difficult
to climb stairs or stand without help.
By age 12, most boys use a wheelchair.
Scoliosis (a side-to-side spine curvature)
and (a front-to-back curvature) often appear at
this time. DMD
also causes diaphragm weakness, so it is difficult
to breathe and cough.
This affects the child’s energy level and increases lung
infections. With
the help of a ventilator, patients with DMD often
live into their twenties and beyond. About one
third of DMD patients have some learning
disabilities that require individualized
educational plans.
Emery-Dreifuss
muscular dystrophy (EDMD):
This type of muscular dystrophy usually
begins with muscle contractures, and then
progresses to muscle weakness that affects the
shoulder and upper arm.
The weakness then progresses to the calf
muscles. Most men with EDMD can live into middle
age.
Another symptom of EDMD is a defect in the heart's rhythm
(heart block), which is usually treated with a
pacemaker.
Facioscapulohumeral
muscular dystrophy (FSH): Symptoms of FSH are
vary greatly.
They most commonly begin in the teens or
early twenties, but infant or childhood onset has
been documented.
Symptoms usually begin with difficulty
lifting objects above the shoulders. The weakness
in the shoulders causes scapular winging, where
the shoulder blades stick out sharply from the
back. Muscles
in the upper arm often lose bulk sooner than the
forearm. Symptoms
related to facial weakness include loss of facial
expression, difficulty closing the eyes
completely, and the inability to drink with a
straw, blow up a balloon, or whistle.
Contracture of the calf muscles may cause
frequent tripping over curbs or uneven areas.
The earlier the onset of symptoms, the more
likely the patient is to need a wheelchair for
mobility. Children
with FSH often develop partial or complete
deafness.
Limb-girdle
muscular dystrophy (LGMD):
While there are many forms of LGMD, two
major clinical forms are most commonly recognized.
One is a severe childhood form that is similar in
appearance to DMD.
The second form appears in a person's teens
or twenties. Symptoms include progressive weakness
and loss of the muscles closest to the trunk. Leg
contractures may occur.
The patient usually loses the ability to walk about 20 years
after the onset of symptoms.
Some people with LGMD need to use a
ventilator because of respiratory weakness.
Lifespan may be slightly shortened.
Myotonic dystrophy:
Symptoms of myotonic dystrophy include
facial weakness and a slack jaw, drooping eyelids
(ptosis), and muscle loss in the forearms and
calves. Other
symptoms may include difficulty relaxing the
grasp, especially with cold objects; heart
arrhythmias and block; constipation; cataracts;
retinal degeneration; low IQ; frontal balding;
skin disorders; atrophy of the testicles; sleep
apnea; and insulin resistance. People with
myotonic dystrophy usually experience low
motivation and an increased need for sleep. Most
sufferers are severely disabled within 20 years of
the onset of symptoms, but do not require a
wheelchair.
Oculopharyngeal
muscular dystrophy (OPMD):
Symptoms of OPMD are confined to weakness
in the muscles controlling the eyes and throat.
Symptoms include drooping eyelids and
difficulty swallowing (dysphagia).
The weakness progresses to other muscles of
the face and neck, and can occasionally affect the
upper parts of the legs.
Dysphagia can cause food or saliva to enter the airways,
called “aspiration,” which can cause
pneumonia.
How
is it diagnosed?
To diagnosis any form of
muscular dystrophy, your physician will take a
careful medical history and perform a thorough
physical exam.
Because these diseases are genetically
inherited, your family history may be an important
source of information.
Lab tests may include blood level of the
muscle enzyme creatine kinase (CK); muscle biopsy;
Electromyogram (EMG) to check muscle response when
stimulated; and genetic tests for the presence of
the mutated gene for DMD, BMD, DM, several forms
of LGMD, and EDMD.
An electrocardiogram may also be needed.
What
is the treatment?
There are no cures for any of
the muscular dystrophies and few drugs that have
any effect. Treatment of muscular dystrophy is
mainly directed at preventing the complications of
weakness, including decreased mobility and
dexterity, contractures, scoliosis, heart defects,
and respiratory weaknesses.
Treatment is centered on physical
and occupational therapy.
However, surgery may be necessary to
correct severe contractures, compensate for
shoulder weakness, lift eyelids that are affected
by OPMD, correct scoliosis, and to keep the
airways open in cases of sleep apnea.
The selection of anesthesia is critical in
muscular dystrophy patients because of the
possibility of malignant hyperthermia, a severe
reaction to halothane anesthetic. Specific
treatments depend upon the type of muscular
dystrophy you have been diagnosed with.
Self-care
tips
There is currently no way to
prevent muscular dystrophy if you have inherited
the genes responsible for these disorders.
However, accurate genetic tests are now
available for the muscular dystrophies for which
the mutated gene has been identified.
These can be useful for family planning
purposes for those with a family history of this
disease.
If you have been diagnosed with a form of
muscular dystrophy, good nutrition is an important
part of your general health.
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
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