Multifocal Motor Neuropathy
What is Multifocal Motor Neuropathy?
Also known as MMN, multifocal motor neuropathy is a condition that affects the motor nerves. These are the nerves that bring about and control the movement of the muscles. MMN affects the delivery of nerve signals, leading to weakness in the upper limbs, cramps and muscle twitching.
In most cases, MMN is diagnosed during middle age. However, it can affect adults of all ages. MMN is not a life-threatening condition and treatment can make a very positive difference. Symptoms vary according to the individual and may be very mild.
What causes multifocal motor neuropathy?
Multifocal motor neuropathy is an autoimmune condition, but it is not known what causes it. Autoimmune disorders occur when the body mistakenly reacts to a harmless trigger, which it perceives to be a threat. In this case, the body produces an immune response and starts to attack the nerve cells.
What are the symptoms?
Usually, the arms and hands are affected first and symptoms include muscle weakness, cramps and uncontrollable twitching. In most cases, symptoms tend to be worse on one side of the body than the other. As symptoms progress, the legs may also be affected.
MMN does not cause any pain and doesn’t affect your ability to feel, as the sensory nerves are not involved. Symptoms tend to progress with age.
How is multifocal motor neuropathy diagnosed?
Sometimes, MMN may be misdiagnosed because it causes symptoms that are similar to other conditions, such as ALS (amyotrophic lateral sclerosis). If MMN is suspected, a GP will refer a patient to a specialist neurologist for further tests. A diagnosis can usually be reached suing the findings of:
- blood tests: including tests to check the levels of GM1 antibodies, which may be higher in people with MMN
- nerve conduction tests: these tests measure the speed at which electric signals travel through the nerves
- EMG (electromyography): this test measures the activity of specific nerves
In very mild cases, symptoms can usually be managed effectively without any formal treatment. In more severe cases, treatments such as intravenous immunoglobulin may be used to strengthen the muscles. The effects of treatment tend to last up to 6 weeks and treatment may be repeated frequently, usually around once a month. Immunoglobulin treatment does not have any side-effects.
If immunoglobulin treatment is unsuccessful, a drug called Cytoxan (cyclophosphamide) may be recommended.
Therapies such as physiotherapy can also be beneficial for strengthening the muscles and helping to reduce weakness.
It is also important for patients to practise self-help techniques and take care to look after themselves.
What is the outlook?
In mild cases, patients are able to continue with many of their day to day activities without any problems. However, in more severe cases, this condition can take its toll and even the most basic activities can become more difficult. This may relate to large muscle movements as well as fine motor skills, such as doing up buttons, for example.