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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 one 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:
Your symptoms may differ from those described above. The different forms of DD may cause slightly different symptoms and progression.
Your doctor will start by taking your health history, asking about your recent symptoms, past health conditions, and your family health history. The doctor will give you a physical exam and test your muscle strength. You may need other tests. These include:
You may first see your primary doctor but then be referred to a neurologist. Some neurologists have special training to treat nerve and muscle diseases. Your doctor 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:
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.
Tips to help you get the most from a visit to your healthcare provider:
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