What Is Multifocal Motor Neuropathy?
Multifocal motor neuropathy (MMN) is a disease that affects your body's motor nerves. Those are the nerves that control your muscles. The condition makes it hard for them to send the electrical signals that move your body, which makes your hands and arms feel weak. They’ll also twitch and cramp.
MMN is not life-threatening, and, in most cases, treatments can make the muscles stronger. The disease can get worse slowly, and after a while, you may have a hard time doing daily tasks, like typing or getting dressed. But for many people, symptoms may be so mild that they don't need treatment at all. You may be able to work and stay active for many years after your diagnosis.
Most people are diagnosed with MMN in their 40s and 50s, although adults from ages 20 to 80 can find out they have the disease.
No one knows what causes MMN. Scientists do know it’s an autoimmune disease, meaning your immune system mistakenly attacks your nerve cells as if they were invaders. Researchers are studying the disease to try to find out why it happens.
If you have MMN, you’ll most likely notice the first symptoms in your hands and lower arms. Your muscles may feel weak and cramp up or twitch in a way you can’t control. It may start in specific parts of the arm or hand, like the wrist or finger. Usually the symptoms are more severe on one side of your body. The disease may eventually affect your legs.
MMN isn’t painful, and you’ll still be able to feel with your hands and arms because your sensory nerves are not affected. But your symptoms will slowly get worse as you get older.
Getting a Diagnosis
Doctors often mistake MMN for amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease. They have similar symptoms, like twitching. Unlike ALS, though, MMN is treatable.
Your doctor may tell you to see a neurologist, a specialist who treats problems with the nervous system. They will give you a physical exam and also ask questions about your symptoms, like:
- Which muscles are giving you trouble?
- Is it worse on one side of your body?
- How long have you been feeling this way?
- Do you have any numbness or tingling?
- Does anything make your symptoms better? What makes them worse?
The doctor will do some nerve and blood tests to rule out other conditions that might cause your symptoms. They may do:
- A nerve conduction study (NCS). This test measures how fast electrical signals travel through your nerves. Usually your doctor will put two sensors on the skin over one of your nerves: one to transmit a small electric shock and the other to record the activity. The doctor will repeat the test on other nerves if they think that more than one is involved.
- A needle electromyography (EMG). Your doctor will put electrodes on your arms. The electrodes have small needles, which go into your muscle, and they’re attached by wires to a machine that can measure the electrical activity in your muscles. Your doctor will ask you to slowly flex and relax your arms so the machine can record the activity. The doctor can do this test at the same time as the NCS.
- A blood test to look for GM1 antibodies, part of your body’s immune system. Some people with MMN have higher levels of them. If you do have a lot of these antibodies, chances are you have the disease. You might have MNN even if you don't have a lot of the antibodies, though.
Questions for Your Doctor
- How will MMN affect me?
- Do I need treatment?
- What kinds are available?
- How will they make me feel?
- Will I be able to work?
- What happens if the treatment doesn't help?
- Are there any clinical trials I can join?
- Are there any activities I won't be able to do?
If your symptoms are very mild, you may not need any treatment. If you do need treatment, your doctor will probably prescribe a medication called intravenous immunoglobulin (IVIg). You’ll get the drug directly into one of your veins through an IV. You’ll usually get it in a doctor's office, although you can learn to do it at home.
If IVIg works, you should feel your muscle strength improve within 3 to 6 weeks. The effects will wear off over time, though, so you’ll need to keep having the treatment. People usually have it once a month, but it may be more or less often depending on your condition.
IVIg doesn't have many side effects, but it is expensive.
Doctors are testing ways to give it directly through the skin like a regular shot, but this method isn’t available for everyone.
If IVIg doesn't work, your doctor may try a drug called cyclophosphamide (Cytoxan), which is also used to treat certain types of cancer. This drug controls symptoms by turning down your immune system. Unlike immunoglobulin, cyclophosphamide can have bad side effects, so doctors try not to use it.
Taking Care of Yourself
If you get treatment for MMN early, you’re more likely to have few symptoms or long-term problems. Stick to your treatment plan, and talk to your doctor about any changes in how you’re feeling.
If you have trouble with certain activities, you may want to see an occupational or physical therapist. They can help you keep your muscles strong and show you how to do daily tasks more easily if your muscles are bothering you.
What to Expect
Many people with MMN can continue most or at least some of their normal activities. The disease can get worse for some people and keep them from doing daily tasks.
The kind of problems you have depend on which of your muscles are affected. If your hand muscles are weak, you may have trouble eating, typing, writing, or buttoning clothes. If your leg muscles are affected, you could have trouble walking. Some people with severe MMN have trouble in all these areas.
To learn more about multifocal motor neuropathy, visit the web sites of the Neuropathy Action Foundation, the Neuropathy Association, or the GBS-CIDP (Guillain-Barre Syndrome-Chronic Inflammatory Demyelinating Polyneuropathy] Foundation International.