What is the Difference Between Multiple Sclerosis (MS) and Muscular Dystrophy (MD)?

In multiple sclerosis, the body's immune system appears to attack the outer layer of the nerves, particularly in the brain, spinal cord, and optic nerve, eventually breaking this layer (called myelin) down. This means that signals sent along those nerves are slowed down or cannot travel at all. No one is sure why this happens, so researchers don't know the exact causes of the disease. It is thought that genetics likely plays a part, but other factors — like a virus or environmental conditions — may be involved.

Muscular dystrophy, on the other hand, is genetic. In most cases, a gene that controls the production of certain types of proteins doesn't work correctly, causing muscle fibers to break down. There are many different types of MD, including a number of other closely related conditions, so the exact causes vary with the type of MD. Duchenne MD is believed to be one of the most common forms. It's caused by a defective gene on the X chromosome and prevents the body from producing a protein called dystrophin, which is needed for the cell membranes of muscle fibers.

MS is more common in women than men, which is also true of other autoimmune diseases. Diagnosis typically occurs between the ages of 20 and 50, although it can affect younger people as well. How genetics plays a role in MS isn't clear, but people who have family members with the disease are much more likely to develop it as well. It affects people of nearly all races, although people of northern European ancestry seem more susceptible, as are people who live farther from the equator in general.

The most common types of muscular dystrophy affect boys, often those who are very young. The symptoms of Duchenne MD often start before the age of 5, and it's usually well advanced by the time a boy is 12. A similar condition, Becker muscular dystrophy, often develops when a child is older, often around age 10 or even later. The symptoms of Emery-Dreifuss MD are usually present by the age of 10, and heart problems often develop by 20.

Other types of muscular dystrophy, including limb-girdle, myotonic, fascioscapulohumeral (FSHD), and congenital MD, can affect both men and women. There are congenital forms of MD that are present at the time of birth, whereas other types often develop when a person is in his or her teens or 20s. Oculopharyngeal MD usually does not appear until later in life, often after a person is in his or her 50s.

Some of the symptoms of multiple sclerosis and muscular dystrophy can be similar, which is one reason why they may be confused. Muscle weakness is common in both conditions, and problems walking and running can be seen in MS and some types of MD. People with MS are more likely to develop additional symptoms, like dizziness, vision problems, tingling or numbness, and feelings of electric shocks. Different forms of MD affect different parts of the body, so muscle weakness may be seen mostly in one area: the face with myotonic MD, for example, or the shoulders with FSHD.

MD tends to be very difficult on the body as the muscle fibers break down. Most forms will ultimately cause death as the muscles become weak and atrophied. People with some of the most common forms often are unable to walk as the disease progresses, and may develop problems with their joints and spinal cord.

Those with MS usually don't have constant symptoms, although an attack can last for months in some cases. These attacks can temporarily impair movement, cause vision problems, and give the sufferer great pain. Symptoms often go away, especially in the early stages of the disease, and a person with the condition may go through long periods with no problems at all. As the disease worsens, however, attacks may become more frequent, and the person less likely to recover from them.

A medical professional typically diagnoses MS based on MRI scans of the brain and spinal cord, nerve function tests, and a lumbar puncture. He or she will also typically examine the eyes for irregular responses of the pupils and other vision problems. A neurological exam to test movement in the arms and legs, reflexes, and changes in sensation in any part of the body may also be conducted.

Tests for MD include muscle function tests and a muscle biopsy in some cases. Some types often have clear physical symptoms. Blood tests are often performed to find the levels of certain enzymes, including creatine kinase. DNA tests may be used to look for specific genetic mutations found in some forms of the disease.

Some medications, including fingolimod and interferons, may help reduce the number of MS attacks and slow progression of the disease in some patients. Corticosteroids are often used to relieve the inflammation associated with attacks, and muscle relaxants may help with the pain and stiffness. Physical therapy is often recommended to help the patient maintain muscle tone.

People with MD may also experience benefits from physical therapy, which often helps the person keep more muscle function. As with MS, corticosteroids are often prescribed, and may help maintain muscle strength. Once the disease progresses, wheelchairs and braces may be needed so that the patient can stay mobile. People with spinal problems related to MD may need surgery to make breathing easier. A pacemaker may also be required if the heart is affected by the disease.