Inherited myopathies or MD |
- Muscular dystrophy (MD) refers to an inherited group of diseases characterized by progressive myopathy (muscle weakness and destruction).
- The group of muscular dystrophies includes Duchenne's MD, Becker's MD, Emery-Dreifuss MD, limb-girdle MD, congenital MD (i.e., Fukuyama, Walker-Warburg, muscle-eye-brain, merosin type, and integrin type), distal MD (Welander, Markesbery, Nonaka, Miyoshi, and Laing) and others (Bethlem, myofibrillar, myotonic, oculopharyngeal, and facioscapulohumeral).
- The disease groupings are further distinguished by differences in distribution and severity of weakness (which muscles are affected first), age of onset, inheritance, and rate of progression.
Duchenne's MD -- starts at ages 2-6, affecting the
pelvis, upper arms, and upper leg muscles first. At ages
2-3, there is difficulty running. At ages 5-6, there is
difficulty climbing and getting up from a chair or bed, and
by age 12, most patients have contractures (limbs are stiff,
frozen in bent position) and are confined to a wheel chair.
- At first, the calf muscles
(behind the leg) are enlarged. When walking stops, all
muscles atrophy, becoming small and useless. Weakness of
muscles in the spine leads to a change in normal curvature
and stooped posture (kyphoscoliosis) develops.
- The heart muscle is weakened
(cardiomyopathy) and fails to pump blood to the rest of
the body, causing shortness of breath with activity,
swollen ankles, and fluid in lungs.
- Arrythmias -- dystrophic heart
muscles have their normal electrical pathways blocked by
fat and connective tissue. These pathways are necessary
for the regular and rhythmic pumping action of the heart.
When blocked, dangerous arrythmias (no rhythm) occur.
- By age 10, the respiratory
(breathing) muscles of the lungs are affected, and by age
20, most patients die from lung infection.
- There may be a mild decline in
- Becker's MD -- starts between the ages of 5-15 and is a milder and slower form of Duchenne MD. The patients live longer and are able to walk until age 30.
- Heart and lung problems are similar to Duchenne MD.
- Emery-Dreifuss -- begins in childhood with a weakness in the upper arms and lower legs, spreads to the chest and pelvis, with contractures of the elbows, ankles, and posterior of the neck. Most patients can walk until age 30-40
- Distal MD -- affects the muscles farthest from the center (distal) of the body (hands, lower part of legs), progressing to more central muscles over time. Ultimately, there is difficulty with grabbing, use of the arms, and walking.
- Welander MD develops at age 40-60, causing weakness and atrophy of the muscles that help extend the forearm and control the small muscles of the hand. Later, the muscles of the front of the leg and the small foot weaken, resulting in the inability to keep the foot straight.
- Miyoshi MD -- the muscles affected are those of the calf in the back of the leg.
- Oculopharyngeal MD (age 40-60) -- first there is drooping of the eyelids (ptosis) and weakness of throat muscles that results in difficulty swallowing (dysphagia). Later, there is weakness in other muscles in the body (hips and shoulders) that affects lifting and walking, and lung infection. Death may result from aspiration (i.e., swallowed food or saliva ends up in the lungs). Malnutrition can occur.
- Limb-girdle MD refers to a group of disorders (age 3-30) that first affect the muscles of the hips (limb) and shoulders (girdle). These diseases progress slowly and by age 20, there is major difficulty in raising or lifting objects above the shoulders (shoulders slump forward), walking, or climbing stairs.
- Fascioscapular MD can present in childhood or adulthood. The muscles of the face are first affected, followed by the muscles of upper back (around the scapular bone). There is a slow (at times could be rapid) progression to the upper arms and front muscles of the legs.
- There are no expressions on the face (mask-like), and when the arms are raised, the shoulder blades (scapular region) look like two wings (due to weakness of muscles).
- As the upper arm muscles atrophy (underused, wasted, and weak), the forearms (not atrophied) recall "Popeye's".
- Later, there is weakness of the leg muscles, causing the foot to drop and drag while walking.
- Myotonic MD -- the first muscles affected (at any age) are the face, feet, and front of the neck.
- The muscles are stiff.
- There is facial weakness (inability to make faces, droopy eyelids), inability to touch the chin to the chest, to keep the neck straight (keeps falling backward), and frontal baldness.
- The temples (muscles on either side of forehead) may have a depressed appearance.
- Cataracts (the lens of the eye becomes cloudy) -- blocks normal vision (everything is cloudy).
- Testicular atrophy (testicles shrink), and impotence (inability to have or maintain an erection).
- Swallowing difficulty (food gets stuck in throat).
- Heart disease -- fainting, dizziness, and a feeling that your heart is racing so fast that it seems as if it may burst.
- Sleeping problems -- sleeping too much at times
- Mild emotional and intellectual impairment -- the patient is slow when it comes to learning.
- Females with myotonic MD can pass the defect on to offspring.
- Congenital MD's -- present at birth:
- Infants have contracture (bent and frozen) of elbows, hips, knees, and ankles.
- In some, there are problems with the brain and the nervous system (speech problems, learning difficulties, Seizures, and blindness).
- Genetics -- human cells contain many genes (strings of DNA) that provide the blue print for making specific proteins needed for normal cell function (i.e., muscle cells). Chromosomes carrying DNA are passed down from parent to child (inherited) and may carry defective genes. In MD, the defective genes cannot produce the proteins (or produce the wrong amount) necessary for normal muscle functions, resulting in symptoms of muscle weakness and dystrophy (i.e., hard, thick material comprised of connective tissue and fat replaces the normal muscle).
- In Duchenne's (no protein is produced) and Becker's MD (abnormal sized protein or amounts is produced), the defective gene is located on the female chromosome (X), and the affected protein is dystrophin.
- Emery-Dreifuss is also carried on the X chromosome (X-linked), and the protein affected is called emerin.
- In myotonic and oculopharyngeal MD, the defective genes are on chromosome number 19 and 14, respectively.
- In other types of MD, locations of defective genes and proteins have been identified.
- Physical exam and a detailed medical history will help to correctly diagnose the type of MD.
- The tests done often depend upon the particular MD type and the organs affected (see above).
- Blood analysis -- creatine kinase (CK) is present in normal muscle cells
- When muscle cells are injured as in MD, CK leaks into the blood. In MD, the amount of CK varies from normal to high, depending on the type and extent of injury.
- DNA analysis -- blood is taken, and the DNA in the white blood cells is analyzed for the defective gene.
- Blood is taken (from veins in the arms) for hormones (thyroid, corticosteroids) and chemicals (glucose, potassium, liver, and kidney functions).
- Muscle biopsy -- small piece of affected muscle is removed (with a needle or by cutting), and sent for examination (looked at under a microscope).
- The diseased muscle of patients with MD when examined under a microscope shows dystrophic changes (variable muscle fiber size, dead muscles, and presence of fat and connective tissue).
- DNA of the muscle sample taken at the biopsy can also be examined for the defective gene.
- Electromyography (EMG), which measures muscle function in response to an electrical stimulation (needles are inserted in to the muscle), is often needed if the DNA analysis is not helpful.
- Nerve conduction study -- only done if the physician suspects diseased nerves as the cause of muscle weakness.
- Electrocardiogram (EKG) can tell the doctor if the normal electrical pathways of the heart muscle are affected by MD.
- Echocardiography uses sound to see the structure and assess the function of the heart.
- A chest X-ray will show the lungs and the size of the heart.
- An examination of the eyes using an ophthalmoscope (helps the doctor to see inside the eye) is done. The procedure is painless.
- Vision is tested using eye charts.
- Hearing may need to be tested.
- Swallowing is evaluated by a speech therapist who may recommend that a swallowing test be done (X-rays or video taken after swallowing food or barium). This is also painless.
- An IQ test (uses problem solving games and toys) can detect if there is mental retardation.
- A neurologist (a specialist in muscles and nerves) is often involved.
- A psychiatrist is needed if the patient is depressed.
- Sleep studies (a camera records the sleeping patient) may be done if there are sleep problems.
- Family history of MD
- Only the male children of X-linked type MD (Duchenne's, Becker's, or Emery-Dreifuss) all have the disease.
- Autosomal dominant (need only one defective gene from one parent to cause MD) -- Markesbery, Welander, Laing, facioscapular, oculopharyngeal, myotonic, myofibrillar, Bethlem, and some types of limb-girdle MD. These are seen in both males and females.
- Autosomal recessive (one defective gene from both parents are needed to cause MD) -- congenital (present at birth), Nonaka, Miyoshi, and some types of limb-girdle MD are seen in both males and females.
- Medications can help if there are infections, heart failure, Depression, or if hormones are needed.
- Oxygen is given if there is shortness of breath.
- For pain, Tylenol and other painkillers (aspirin and Ibuprofen) are given.
- Medications may help with stiffness or contractures (Baclofen and other muscle relaxants).
- Devices such as braces (for neck, foot, arms, or trunk)
- Walkers, canes, and wheel chairs are helpful in improving mobility.
- Exercise, massage, and physical therapy can help weakened muscles, prevent contractures, and reduce pain and stiffness.
- Surgical procedures done in the hospital can remove Cataracts, correct contractures, and correct dangerous heart rhythms by implanting a pacemaker.
- Respirators or ventilators are devices that can assist the patient who can no longer breath on his own.
- Gene therapy, in which the defective gene or protein is replaced, promises a cure.
If you suspect that your child has this condition, consult with your physician and neurologist. Ask about new treatments (gene therapy), and remember that all complications and symptoms can be dealt with if identified early. More information can be obtained from the Muscular Dystrophy Association by calling 1-800-572-1717.
- Endocrine myopathies such as hypo- or hyperthyroidism
- Myasthenia Gravis
- Drug-induced myopathies (corticosteroids, Lovastatin, alcohol, colchicines)
- Eaton-Lambert syndrome
- Polymyalgia rheumatica