Distal muscular dystrophy (DD) is a group of rare diseases that affect your muscles (genetic myopathies). DD causes weakness that starts in the lower arms and legs (the distal muscles). It then may gradually spread to affect other parts of your body. The muscles shrink (atrophy). DD has several forms. DD usually appears between ages 40 and 60. But it can sometimes show up as early as the teenage years. DD affects both men and women.
All forms of DD are caused by changes (mutations) in certain genes. Changes in several different genes can cause different types of DD.
Muscles are made up of bundles of long muscle fibers (muscle cells). These fibers contract when nerve signals from the brain go to the specific spot (junction) where the nerve activates the muscle. In some cases, the mutations that cause DD are in genes that make certain molecules within muscle cells.
The genes in your body usually occur in pairs. You inherit a copy from each parent. 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.
Because the genetic defects that cause DD are usually passed on through families (hereditary), you have a higher risk for DD if the condition runs in your family. Some forms of DD are much more common in certain groups. For example, Nonaka distal myopathy most commonly appears in people of Japanese descent. Finnish (tibial) distal myopathy happens more often in people of Finnish descent.
The main symptom is muscle weakness. DD affects mainly the muscles of the lower legs and arms. These muscles lose mass and strength. This may affect how well you can grip things, use a pen, or type. It may also cause problems walking. Some forms of DD cause foot drop. This means difficulty lifting the foot. With foot drop, you may drag your feet or lift your knees to walk with high steps.
In some cases, DD may affect other muscles. Depending on the form of DD you have, the weakness may also affect the muscles in the neck, hands, hips, trunk, or even the heart. Sometimes DD affects the thighs. But in other cases, the upper legs remain strong. Certain types of DD cause trouble with speaking or swallowing.
The main symptom is 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 ages 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.
Your healthcare provider will start by taking your health history, asking about your recent symptoms, past health conditions, and your family health history. He or she will give you a physical exam and test your muscle strength. You may need other tests. These include:
Blood tests, for muscle enzymes such as creatine kinase
DNA blood tests, for known DD changes
Muscle biopsy, to look for the specific problem in the muscle cells
Electromyography, to measure the electrical activity of the muscles
MRI or ultrasound tests, to look at the muscles
You may first see your main healthcare provider but then be referred to a neurologist. Some neurologists have special training to treat nerve and muscle diseases. Your healthcare provider also may refer you to a clinic that specializes in managing DD.
There is no cure for DD. But supportive care can help you keep your strength and flexibility. Physical therapy is important to keep your range of motion. Occupational therapy can help with ways to adapt for activities such as eating, walking, or computer use. You also may get help from certain aids. These include:
Lower-leg braces to treat foot drop
Other lightweight leg braces for support
Mouse and keyboard alternatives
Cuffs, braces, openers, and other adaptive devices
Depending on the form of DD and the muscles involved, complications may include difficulty with walking, swallowing, or other activities, usually beginning in later adulthood. If you have a form of DD that sometimes affects the heart, you may need to be monitored for irregular heart rhythms. Some forms of DD can also cause problems with breathing. In these uncommon cases, you may eventually need a breathing machine.
DD generally tends to develop in adults and gets worse slowly. Occupational therapists can help you learn adaptive techniques. These may include using leg braces and wrist devices. You may also need to use special devices when working at a computer or for other daily activities.
Work with your healthcare team to make a safe exercise plan. Some forms of exercise can be harmful if you have DD. Range-of-motion exercises are usually part of an exercise plan. Check with your team to find out about the best exercise program for you. You may also get more information about DD by visiting the Muscular Dystrophy Association.
DD is a rare genetic condition that causes muscle weakness. It usually begins in adulthood and has several forms.
DD usually affects the muscles in the lower arms or leg. But it may also affect other parts of the body.
DD usually shows up between ages 40 and 60, but it can sometimes show up as early as the teenage years.
Work closely with your healthcare team to manage DD. You will probably need physical therapy and supportive treatment.
Tips to help you get the most from a visit to your healthcare provider:
Know the reason for your visit and what you want to happen.
Before your visit, write down questions you want answered.
Bring someone with you to help you ask questions and remember what your provider tells you.
At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
Ask if your condition can be treated in other ways.
Know why a test or procedure is recommended and what the results could mean.
Know what to expect if you do not take the medicine or have the test or procedure.
If you have a follow-up appointment, write down the date, time, and purpose for that visit.
Know how you can contact your provider if you have questions.