Muscular dystrophy

Muscular dystrophy is a group of inherited genetic disorders in which there is a progressive weakness and degeneration of skeletal muscles.

Skeletal muscles refer to the muscles that are attached to the bones and allow voluntary movements.

Muscular dystrophy is caused by genetic mutations that affect the essential proteins for the normal structure and function of muscle fibers. It can lead to a progressive weakness, loss of muscle mass and muscular atrophy.

In some types of muscular dystrophy not only the muscle are affected, but also the heart, the lungs or other organs.

There are nine main types of muscular dystrophies generally recognized:

1. Duchenne muscular dystrophy (DMD): It is the most severe form of this disorder. It affects young boys, causing progressive muscle weakness. It usually begins in the legs and they usually have problems when jumping, running or climbing stairs.
2. Becker muscular dystrophy (BMD): It has a milder course than Duchenne muscular dystrophy. It affects older boys and young men.
3. Emery-Dreifuss muscular dystrophy (EDMD): It affects young boys, causing contractures and weakness in the calves, weakness in the shoulders and upper arms, and heart conduction defects. It is extremely rare.
4. Limb-girdle dystrophy (LGMD): It begins in late childhood and continues into early adulthood. It may affect both men and women. This disorder causes weakness in the muscles around the hips and shoulders. It is the most variable of all muscular dystrophies, with multiple subtypes.
5. Facioscapulohumeral muscular dystrophy (FSHD) or Landouzy-Dejerine muscular dystrophy: it begins during late childhood or early adulthood, affecting both men and women. It causes weakness in the muscles of the face, shoulders, and upper arms. The hips and legs may also be affected.
6. Myotonic dystrophy or Steinert's disease: It affects both men and women, causing general weakness of the face, feet, and hands. It is characterized by the inability to relax the affected muscles (myotonia). Symptoms may start from birth through adulthood. This type of muscular dystrophy is the most common.
7. Oculopharyngeal muscular dystrophy (OPMD): it affects both adult men and women, causing weakness in the muscles of the eye and throat.
8. Distal muscular dystrophy: it begins in late adolescence or early adulthood, causing weakness in the muscles of the feet and hands. It is more common in Sweden and rare in other countries.
9. Congenital muscular dystrophy: Present from birth. It is a rare condition. This disorder produces general weakness that progresses slowly. A subtype called Fukuyama, most common in Japan, involves mental retardation.

Muscular dystrophies are genetic diseases, which means they are caused by genetic disorders.

Some of these disorders, such as Duchenne, Becker, congenital dystrophy, and most types of Limb-girdle dystrophies are due to defects in genes that affect certain muscle proteins that lead to the muscle deterioration.

In Duchenne (DMD) and Becker (BMD) dystrophy a protein called dystrophin is affected, while in Emery-Dreifuss dystrophy a protein called emerin is affected.

Myotonic dystrophy is linked to a gene defect in a protein that control the flow of charged particles within muscle cells.

Duchenne, Becker, and Emery-Dreifuss muscular dystrophies are inherited with X-linked recessive inheritance. This means that only the male sex may be affected, but women can be carriers of the disease.

The main symptom of muscular dystrophy is muscle weakness.

The intensity of the symptoms, age of onset, and progression of the disease differs depending on the type of muscular dystrophy.

Sometimes, joint pain may occur due to muscle weakness.

According to the type of muscular dystrophy, the symptoms will be specific for each type:

1. Duchenne muscular dystrophy (DMD): It especially affects the muscles of the legs. Children tend to have balance and walking problems. Additionally, weakness of the diaphragm can occur. The diaphragm is the muscle that helps with breathing and coughing. The weakness of this muscle may increase lung infections.
2. Becker muscular dystrophy (BMD): The progression of this type of dystrophy is similar to that of Duchenne, but the symptoms are milder and the course more variable. It may follow the same pattern of leg weakness and instability. Cardiomyopathy (a disease of the heart muscle) may occur more frequently in this type of disorder.
3. Emery-Dreifuss muscular dystrophy (EDMD): This type of muscular dystrophy begins with contractures that precede muscle weakness. The weakness mainly affects the shoulders and upper arm, along with the calf muscles. People who suffer this type of muscular dystrophy usually require pacemakers to avoid heart blocks.
4. Limb-girdle dystrophy (LGMD): It is characterized by progressive weakness and atrophy of the muscles closest to the trunk. Contractures may occur, and the ability to walk is usually lost approximately 20 years after the onset of the symptoms. Some people may develop respiratory weakness that requires the use of a ventilator.
5. Facioscapulohumeral muscular dystrophy (FSHD) or Landouzy-Dejerine disease: The first symptom is usually difficulty lifting objects above the shoulders. The disease is named for the regions of the body most severely affected by the disease: muscles of the face (facio), shoulders (scapula), and arms (humeral). The hips and legs may also be affected.
6. Myotonic dystrophy or Steinert's disease: Symptoms may include facial weakness, drooping eyelids (ptosis), and muscle atrophy in the forearms and calves. This type of disease can affect the heart muscle, causing arrhythmias and heart blocks. The muscles of the digestive system may also be affected, leading to motility disorders and constipation.
7. Oculopharyngeal muscular dystrophy: It usually begins with weakness in the muscles of the eyes and throat. Symptoms include droopy eyelids (ptosis) and difficulty swallowing (dysphagia). The weakness may progress to other muscles in the face, neck, and occasionally the upper limbs.
8. Distal muscular dystrophy: It usually begins with weakness in the hands, forearms, and legs. Some of the first symptoms may be difficulty typing or pressing buttons. Symptoms usually progress slowly.
9. Congenital muscular dystrophy: It is characterized by severe muscle weakness from birth. Babies often show displeasure and very little voluntary movement. They may learn how to walk. In contrast, children with the Fukuyama variety rarely learn to walk and have severe mental retardation.

The detection of muscular dystrophy is based on a complete physical exam to determine symptoms and rule out other causes.

Family history may usually give important clues since these diseases are genetic conditions. Most cases are hereditary.

Different diagnostic tests may help detect the disorder:

• CK (creatine kinase) in the blood: This enzyme is usually elevated due to muscle damage even before the first symptoms appear.
• Muscle biopsy: A small piece of muscle is removed and studied under a microscope.
• Electromyography: It is used to know the response of the muscles to stimulation. The response is usually weak if there is muscular dystrophy.
• Genetic test: Used to detect different mutated genes.

Muscular dystrophy can be confused with other diseases that affect the motor neurons, such as Myasthenia Gravis.

There is no cure for any of the muscular dystrophies.

Prednisone, a corticosteroid, can delay the progression of Duchenne muscular dystrophy. Prednisone is also prescribed for Becker muscular dystrophy, although there are no conclusive studies that have proven its benefits. A drug similar to prednisone, deflazacort, appears to have similar benefits with fewer side effects.

The treatment of muscular dystrophy mainly seeks to prevent further complication of muscle weakness, including mobility problems, contractures, scoliosis, heart problems, and respiratory failure. The main therapies used are:

• Physical therapy: Stretching is used to maintain the range of motion of the affected muscles and to prevent or delay contractures. Orthopedic braces are also used, especially on the ankles and feet, to prevent clubfoot. Regular exercise helps maintain good health. High intensity exercises are generally not recommended as it can further damage the muscles.
• Surgery: When contractures become more severe, a type of tendon surgery called tenotomy may be performed. Sleep apnea can also be treated surgically.
  • In facioscapulohumeral muscular dystrophy, surgical fixation of the scapula may help compensate for shoulder weakness.
  • In oculopharyngeal muscular dystrophy, a surgical lifting of the eyelids can be necessary.
  • Surgery to correct scoliosis is often needed in Duchenne muscular dystrophy.
• Occupational therapy: An occupational therapist can suggest techniques and tools to compensate for the loss of strength and dexterity. Strategies may include adaptive utensils and dressing aids, positioning and compensatory movements, or communication aids.
• Cardiac care: Arrhythmias in Duchenne and Becker muscular dystrophy can be treated with antiarrhythmic drugs such as mexiletine or nifedipine. A pacemaker can be implanted if those medications do not show improvement. Heart transplants are becoming more common in people who suffer from Becker muscular dystrophy.
• Respiratory care: People who develop weakness of the diaphragm or other ventilatory muscles may need a mechanical ventilator to aid in breathing.