Trouble using your hands can be caused by a number of conditions, such as arthritis or muscle strain. However, progressive trouble using the hands, arms or legs can be a sign of a serious neurological disease. Many nervous system conditions involve sensation symptoms. However, a rare nerve disorder called multifocal motor neuropathy (MMN) only affects strength.
Due to its gradual onset and lack of sensory symptoms, this condition is sometimes initially mistaken for amyotrophic lateral sclerosis (ALS), a nervous system disorder commonly referred to as Lou Gehrig's disease. However, unlike ALS, multifocal motor neuropathy does not lead to difficulty speaking or swallowing, and is not fatal.
Multifocal motor neuropathy is caused by the immune system attacking part of the nerves that control muscle movement. It is similar to a condition called chronic inflammatory demyelinating polyneuropathy (CIDP). Unlike CIDP and many other types of peripheral neuropathy, multifocal motor neuropathy is not painful and does not typically include numbness or tingling because the sensory nerves aren't affected.
Symptoms of multifocal motor neuropathy
The asymmetrical muscle weakness, spasms, twitching and cramping that comes with this condition usually occurs in one part of the hand or arm. Multifocal motor neuropathy predominantly only affects the upper limbs. However, as the disease worsens, symptoms may eventually extend to the legs or feet. The condition is most common among men younger than 50, but can occur in both genders and at any age.
Since multifocal motor neuropathy shares symptoms with various other nerve disorders, it's important to be seen and evaluated by a neurologist. In addition to reviewing personal and family health history, your doctor will likely use the following diagnostic tests:
- Nerve conduction study to measure the speed of electrical signals through the nerves.
- Needle electromyography (EMG) to evaluate electrical activity in the muscles and the nerves that control them.
- Blood tests to detect unusual proteins and/or measure antibodies in your system.
Treatment of multifocal motor neuropathy
The only treatment approved by the Food and Drug Administration is intravenous immunoglobin (IVIg), antibodies collected from healthy donors. Patients diagnosed with multifocal motor neuropathy usually receive this type of infusion therapy on a monthly basis. IVIg can improve motor function, but treatment needs to be continued on an ongoing basis.