Monomelic amyotrophy

What causes monomelic amyotrophy (MMA)?

The exact cause of monomelic amyotrophy is not well-understood. It is thought that the disease may occur when the material that surrounds the spinal cord (thecal sac or dural sac) shifts in position. This may be caused by repeated downward movement (flexion) of the neck. Changing position of the dural sac can cause pressure to be placed on the spinal cord. This can impact the ability of signals to be sent from the brain to the muscles of the arm. This could cause the signs and symptoms of monomelic amyotrophy. However, it has not been confirmed that pressure on the spinal cord explains why some people develop monomelic amyotrophy. Other possible causes include immune system dysfunction or an infection.

Last updated on 05-01-20

How is monomelic amyotrophy (MMA) diagnosed?

Monomelic amyotrophy (MMA) is suspected when a doctor observes signs and symptoms of the disease such as muscle weakness in one arm only that begins during adolescence or early adulthood. The diagnosis can be confirmed with imaging studies and laboratory tests.

Imaging studies that may help confirm a diagnosis of MMA include MRI or CT scans. These imaging studies may show signs of compression of portions of the spinal cord. Laboratory tests may include an electromyograph (EMG) that shows reduced response in the nerves that carry signals to the arm muscles. Other possible causes of muscle weakness such as trauma or injury must be ruled out to confirm the diagnosis of MMA.

Last updated on 05-01-20

How is monomelic amyotrophy (MMA) inherited?

Monomelic amyotrophy (MMA) is not thought to be caused by changes in a specific gene. Most people who have MMA are the only people with the disease in the family. In some cases, people with MMA reported having other family members with the disease. In one case, it has been reported that two identical twins both developed the disease. This makes researchers think that there may be genetic factors that predispose people to develop MMA. However, not everyone who has these genetic factors would necessarily develop MMA. Instead, it is probably a combination of genetic and environmental factors that cause people to develop MMA.

Last updated on 05-01-20

What is the long-term outlook for people with monomelic amyotrophy (MMA)?

The long-term outlook for people with monomelic amyotrophy (MMA) is generally good. Although symptoms of the disease may progress for a few years after the initial muscle weakness begins, the symptoms generally stabilize. The muscle weakness typically affects one arm and is not associated with pain or other symptoms.

Some people with MMA have loss of function of one hand. This can cause difficulties in caring for oneself, work, and social situations. Sessions with occupational therapists or social workers may help to overcome difficulties associated with muscle weakness.

Last updated on 05-01-20

How might monomelic amyotrophy (MMA) be treated?

Unfortunately, there is no cure for monomelic amyotrophy (MMA). However, there are treatment options that can help manage symptoms of the disease and slow the progression of muscle weakness. If the doctors think that MMA is caused by compression of the spinal cord, they may recommend use of a brace that can be worn around the neck to prevent downward movement (flexion) of the neck. Other treatment options include muscle strengthening exercises and therapies to improve hand coordination. Surgery for the treatment of MMA is debated, as there are benefits and risks associated with surgery. People who are diagnosed with MMA will likely be recommended to see a neuromuscular specialist who can watch for progression of the disease.

Last updated on 05-01-20

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The RareGuru disease database is regularly updated using data generously provided by GARD, the United States Genetic and Rare Disease Information Center.

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