Distal Muscular Dystrophy

Distal myopathy (or distal muscular dystrophy) is a general term for a group of rare progressive genetic disorders characterized by wasting (atrophy) and weakness of the voluntary distal muscles. The distal muscles are those farther from the center of the body and include the muscles of the lower arms and legs and the hands and feet. Conversely, the proximal muscles are the muscles closest to the center of the body such as the muscles of the shoulder, pelvis, and upper arms and legs.

The distal myopathies belong to a larger group of disorders known as muscular dystrophies. The muscular dystrophies are characterized by weakness and degeneration of various voluntary muscles of the body. Approximately 30 different disorders make up muscular dystrophies. The disorders affect different muscles and have different ages of onset, severity, and inheritance patterns.

The main symptom is a weakness that usually starts in the lower arms or legs. But the different forms of DD tend to get worse in different ways. Some examples include:

· Distal myopathy with vocal cord and throat (pharyngeal) weakness affects the hands, legs, and voice. It may cause difficulty swallowing. It usually happens between the ages of 35 and 60.

· Finnish (tibial) distal myopathy affects the legs, particularly the muscles near the shin. It usually shows up after age 40, and most people with this DD can still walk throughout their life. People who inherit 2 copies of the defective gene may have more severe weakness beginning in childhood. They may not be able to walk later. Their heart may also be affected.

· Hereditary inclusion-body myopathy type 2 shows up between ages 25 and 40. It usually weakens the foot and thigh.

· Miyoshi distal myopathy causes weakness that begins in the calf muscles. It shows up between ages 15 and 30. Some people with this form of DD may eventually be unable to walk.

· Nonaka distal myopathy affects the muscles near the shin first. It then affects muscle groups in the upper arm, upper leg, and neck. The thigh muscle (quadriceps) usually stays healthy.

· Welander distal myopathy usually affects the arms first, and then the legs. It shows up in people between ages 40 and 50.

Your symptoms may differ from those described above. The different forms of DD may cause slightly different symptoms and progression.

All forms of DD are caused by changes (mutations) in certain genes. Changes in several different genes can cause different types of DD. A change in only 1 copy of the gene is enough to cause most forms of DD. This means the disease passes down in a dominant manner. In some other types of DD, the disease occurs only if you have changes in both copies of the gene. 

These recessive forms of DD include Nonaka distal myopathy and Miyoshi muscular dystrophy. In Finnish distal myopathy, people with one copy of the changed gene have a weakness in the muscles in the fronts of the lower legs (the tibial muscles) after age 40. People with Finnish DD who inherit 2 changed genes have muscle problems in childhood. They may need a wheelchair by age 30

A diagnosis of distal myopathy is made based upon a thorough clinical evaluation, a detailed patient history, identification of characteristic findings, and a variety of tests including a test that assesses the health of muscles and the nerves that control muscles (electromyography); specialized blood tests; magnetic resonance imaging (MRI) of muscle tissue; and surgical removal and microscopic examination (biopsy) of affected muscle tissue that may reveal characteristic changes to muscle fibers.

• During an electromyography, a needle electrode is inserted through the skin into an affected muscle. The electrode records the electrical activity of the muscle. This record shows how well a muscle responds to the nerves and can determine whether muscle weakness is caused by the muscle themselves or by the nerves that control the muscles.
• Blood tests may reveal elevated levels of the creatine kinase (CK), an enzyme that is often found in abnormally high levels when the muscle is damaged
• MRIs of muscle tissue may reveal a distinct pattern of muscle damage or involvement. Distinct patterns have been identified in individuals with Welander, Udd or Tibial, and other distal myopathies.

Biopsy of affected muscle tissue may reveal characteristic changes such as increased connective tissue and fat. In some forms of distal myopathy, numerous sub-cellular compartments known as rimmed vacuoles can be detected on muscle biopsy.

TREATMENT 

People with distal muscular dystrophy should be monitored throughout their lives. Treatment options include medications, physical and occupational therapy, and surgical and other procedures. Ongoing assessments of walking, swallowing, breathing and hand function enable the treatment team to adjust treatments as the disease progresses.

 Physical Therapy

Several types of therapy and assistive devices can improve the quality and sometimes the length of life in people who have distal muscular dystrophy. Examples include:

·         Range-of-motion and stretching exercises. Muscular dystrophy can restrict the flexibility and mobility of joints. Limbs often draw inward and become fixed in that position. Range-of-motion exercises can help to keep joints as flexible as possible.

·         Exercise. Low-impact aerobic exercise, such as walking and swimming, can help maintain strength, mobility and general health. Some types of strengthening exercises also might be helpful. But it's important to talk to your doctor first because some types of exercise might be harmful.

·         Braces. Braces can help keep muscles and tendons stretched and flexible, slowing the progression of contractures. Braces can also aid mobility and function by providing support for weakened muscles.

·         Mobility aids. Canes, walkers and wheelchairs can help maintain mobility and independence.