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Muscular Dystrophy

Definition


Disease: Muscular Dystrophy Muscular Dystrophy
Category: Bones, joints, muscles diseases
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Disease Definition:

The group of inherited muscle diseases in which muscle fibers are unusually susceptible to damage is called muscular dystrophy (MD). Progressively, muscles, mainly voluntary ones, become weaker. Muscle fibers are often replaced by fat and connective tissue in the late stages of muscular dystrophy. Some types of muscular dystrophy affect heart muscles, other organs and other involuntary muscles.

Genetic deficiency of the muscle protein dystrophin appears to be the cause of the most common types of muscular dystrophy.

The course of the disease can be slowed by therapy and medications; however, there is no cure for muscular dystrophy.

Work Group:


Prepared by: Scientific Section

Symptoms, Causes

Symptoms:

According to the type of muscular dystrophy, signs and symptoms vary. Normally, the symptoms of muscular dystrophy may include the following:

 

  • Progressive crippling, resulting in fixations (contractures) of the muscles around the joints and loss of mobility
  • Muscle weakness
  • Apparent lack of coordination


Among the different forms of MD, specific signs and symptoms vary. Each type is different in how rapidly it progresses, the age of onset and which parts of the body are primarily affected by the symptoms.

DYSTROPHINOPATHIES:
Genetic defect of the protein dystrophin is the cause of these muscular dystrophies.


Duchenne's muscular dystrophy:
This is the most severe form of dystrophinopathy. It is the most common form of MD that affects children, and it occurs mostly in young boys. The following may be included in the signs and symptoms of Duchenne's MD:

 

  • Waddling gait
  • Frequent falls
  • In some cases, mild mental retardation
  • Difficulty getting up from a lying or sitting position
  • Large calf muscles
  • Weakness in lower leg muscles, resulting in difficulty running and jumping


Between the ages of 2 and 3, the signs and symptoms of Duchenne's MD usually appear. The muscles of the pelvis, upper arms and upper legs are first affected by it. Most children with this form of muscular dystrophy are unable to walk by late childhood. Often because of cardiac complications, respiratory muscle weakness or pneumonia, most people with this condition die by their 20s or early 30s. Curvature of the spine (scoliosis) may develop in some people with Duchenne's MD.

Becker's muscular dystrophy:
This is a milder form of dystrophinopathy. It progresses more slowly, usually over several decades, and it normally affects older boys and young men. The signs and symptoms of Becker's MD are similar to those of Duchenne's. The onset of the signs and symptoms may not occur until the mid-20s or even later, though they generally happen around age 11. People that are affected by Becker's MD are usually able to walk through their teens, and often well into adulthood.

Myotonic dystrophy:
The muscle weakness of the other forms of muscular dystrophy, as well as an inability to relax muscles at will (myotonia) and stiffness of muscles are produced by this form of muscular dystrophy, which is known as Steinert's disease.

This form of MD often doesn't affect people until adulthood despite the fact that it can affect children. The severity of the condition can vary greatly. After using the muscles, they may feel stiff. This disease progresses slowly. The following may be included in the signs and symptoms of adult-onset myotonic dystrophy beside myotonia:

 

  • Fainting or dizziness, which may indicate that the disease is interfering with the conduction of electrical signals that keep the heart rate normal.
  • Weakening of head, neck and face muscles, which may result in the face having a hollow, drooped appearance.
  • Frontal balding in men.
  • Weakening of muscles involved in breathing and swallowing. Weaker breathing muscles may result in less oxygen intake and fatigue, while weaker swallowing muscles increase the risk of choking.
  • Clouding of the lenses of the eyes (cataracts).
  • Weakening of voluntary muscles that control the legs and arms, usually beginning with the limb muscles farthest from the torso, such as the muscles of the lower legs, forearms, hands and feet.
  • Weakening of muscles of hollow internal organs such as those in the uterus and the digestive tract. One may experience problems with swallowing as well as constipation and diarrhea depending on which part of the digestive tract is affected. Problems during childbirth may be caused by weakness of the uterine walls.
  • Mild diabetes
  • Difficulty sleeping well at night and daytime sleepiness, and inability to concentrate because of the effect of the disease on the brain.


In a rare case that is called "congenital myotonic dystrophy", infants have this form of muscular dystrophy. Although infants with myotonic dystrophy don't experience myotonia, the infant form is more severe. The following are sings in infants:

 

  • Cognitive impairment
  • Difficulty breathing
  • Severe muscle weakness
  • Difficulty sucking and swallowing


Facioscapulohumeral muscular dystrophy: Progressive muscle weakness that includes the following is involved in this form, which is also called Landouzy-Dejerine dystrophy:

 

  • Upper arms
  • Pelvic area
  • Abdomen
  • Feet
  • Shoulders
  • Lower arms
  • Face


The shoulder blades may stick out like wings when someone with facioscapulohumeral MD raises his/her arms. With some spurts of rapidly increasing weakness, progression of this form is slow. During the teen to early adult years, onset usually occurs. The onset of the disease usually occurs during the teen or early adult years.

Other major types of muscular dystrophy:
The following are included in the other major types of muscular dystrophy:

 

  • Congenital muscular dystrophy
  • Myofibrillar myopathies
  • Emery-Dreifuss muscular dystrophy
  • Limb-girdle muscular dystrophy
  • Oculopharyngeal muscular dystrophy
  • Distal muscular dystrophy


Limb-girdle muscular dystrophy:
The muscles of the shoulders and hips usually affected first by this form of muscular dystrophy.

Limb-girdle MD may start from early childhood to adulthood. Though progression is slow, this form then progresses to the legs and arms.

Congenital muscular dystrophy:
A group of inherited muscular dystrophies are referred to as "congenital muscular dystrophy". Joint deformities and general muscle weakness are some of the signs of this type.  
The congenital MD is either apparent at birth or it becomes evident before the age of 2. Depending on the type, the course of this disorder varies significantly. While some forms of congenital MD progress rapidly and cause severe impairment, others progress slowly and cause only mild disability.

Oculopharyngeal muscular dystrophy:
Usually, drooping of the eyelids is the first sign of this type of muscular dystrophy, and it is followed by weakness of the muscles of the eye, face and throat resulting in difficulty swallowing. The progression is slow. In adulthood, usually in the 40s or 50s is when the signs and symptoms first appear.

Distal muscular dystrophy:
The muscles farthest away from the center of the body (distal muscles), which are those of the lower legs feet, forearms and hands, are involved in this group. This form tends to progress slowly, and the severity is usually less than the other forms of MD. In adulthood between the ages of 40 and 60, is when distal MD begins in general.

Emery-Dreifuss muscular dystrophy:
In the muscles of the shins, shoulders and upper arms is where this form of muscular dystrophy usually begins.  
Other features of Emery-Dreifuss MD are cardiac arrhythmias, stiffness of the spine and muscle contractures. Emery-Dreifuss MD progresses slowly and it usually begins in the childhood to early teen years.

Myofibrillar myopathies (MFMs):
The distal muscles are usually involved as well, though only the muscles closest to the center of the body (proximal muscles) such as the shoulder and hip muscles are affected by MFMs in some cases. usually, this group of muscle disorders is commonly associated with the following:

 

  • Thickening and stiffening of the heart muscle (cardiomyopathy)
  • Muscle contractures
  • Stiffness of the spine
  • Nerve damage (peripheral neuropathy)

 

Although Duchenne's muscular dystrophy can occur in girls, it occurs almost exclusively in boys. As early indication of muscular dystrophy, the young child may appear clumsy and fall often, or may have difficulty climbing the stairs, rising from the floor, running or even walking. A child with MD may exhibit signs of muscle weakness between the ages of 2 and 6, and may learn to walk later than other children do. By the time a child with MD reaches school age, he/she may walk unsteadily and on the toes or balls of the feet.  Children's losing the ability to walk by the age of 12 is usually the result of Duchenne's MD.
Parents should see the doctor if they're concerned about their child's:

 

  • Muscle development
  • Clumsiness
  • Muscle strength
  • Motor abilities


Medications and physical therapy can help slow the progression of muscular dystrophy once it is diagnosed.

If a person is considering having children and to assess the risk of the disease in other family members, genetic counseling may be helpful because muscular dystrophies are inherited disorders.

Causes:

The group of inherited diseases that involve a defective gene is called muscular dystrophy. A genetic mutation that is particular to the type of the disease is the cause of each form of muscular dystrophy. The genetic deficiency of the muscle protein dystrophin is apparently the cause of the most common types of muscular dystrophy.

HOW DOES A PERSON INHERIT DUCHENNE’S OR BECKER’S MD
In a pattern called X-linked recessive inheritance, through one of the mother's genes, Duchenne's and Becker's muscular dystrophies are passed from mother to son. Girls inherit two X chromosomes, one from their mothers and one from their fathers. The X-X combination determines that they are female. Boys inherit an X chromosome from their mothers and a Y chromosome from their fathers. The X-Y combination makes them male.

On the X-chromosome is where the defective gene that causes Duchenne's and Becker's muscular dystrophies is located. Women who have only one X-chromosome with the defective gene that causes these muscular dystrophies are carriers and sometimes develop mild muscle weakness and heart muscle problems (cardiomyopathy). Until another son inherits the defective gene on the X-chromosome, the disease can skip a generation. The disease arises from a new mutation in a gene rather than from an inherited defective gene in some cases of Duchenne's and Becker's muscular dystrophies.

THE DIFFERENT PATTERNS OF OTHER TYPES OF MD:
In a pattern called autosomal dominant inheritance, myotonic dystrophy and most MFMs are passed along. There is a 50% chance the disorder will be passed along to a child if either parent carries the defective gene for myotonic dystrophy.

Some types of muscular dystrophy can be passed on from generation to generation and affect females and males equally. In the same inheritance pattern that marks Duchenne's and Becker's muscular dystrophies, some of the less common types of muscular dystrophy are passed along. And a defective gene from both parents is still required by others.

Complications

Complications:

None

Treatments:

At present, there is no cure for any form of muscular dystrophy. To stop the progression of some types of muscular dystrophy, research into gene therapy may eventually provide treatment. Allowing people with MD to remain mobile as long as possible and preventing or reducing deformities in the joints and the spine are the things that current treatment is designed to do. Various types of medications, assistive devices, physical therapy and surgery may be included in treatments.

MEDICATIONS:
To manage signs and symptoms and slow the progression of muscular dystrophy, medications may be prescribed in some cases:

Muscle deterioration:
The progression of Duchenne's MD may be delayed and muscle strength can be improved by the anti-inflammatory corticosteroid medication prednisone. To delay some damage to dying muscle cells, the immunosuppressive drugs azathioprine and cyclosporin are sometimes prescribed as well.

Muscle spasms, stiffness and weakness (myotonia):
Baclofen, carbamazepine, mexiletine, dantrolene and phenytoin are included in the medications that may be used to help manage myotonia associated with MD.

ASSISTIVE DEVICES:
Slowing the progression of contractures, braces can help keep muscles and tendons stretched and flexible, as well as provide support for weakened muscles of the lower legs and hands. Mobility and independence may be maintained by other devices, such as canes, walkers and wheelchairs. However, using a ventilator may become necessary if respiratory muscles become weakened.

PHYSICAL THERAPY:
Fixations (contractures) can develop in joints as muscular dystrophy progresses and muscles weaken. Restricting the flexibility and mobility of joints, tendons can shorten. The joints of the hips, knees, elbows, feet and hands may be affected by uncomfortable contractures.

Proving regular range-of-motion exercises to keep the joints as flexible as possible, reducing or delaying curvature of the spine and delaying the progression of contractures is the goal of physical therapy. The patient may maintain range of motion in joints by using hot baths (hydrotherapy).

SURGERY:
A tendon release surgery can be performed to release the contractures that may develop and that can position joints in painful ways. The Achilles tendon at the back of the foot, as well as the tendons of the hip and knee can be relieved with surgery. To correct curvature of the spine, surgery may be needed as well.

OTHER TREATMENTS:
It's important to be vaccinated for pneumonia and to keep up to date with influenza shots because respiratory infections may become a problem in later stages of muscular dystrophy.

Prognosis:

Not Available

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