What is Multifocal Motor Neuropathy (MMN)?
MMN is a rare disease that happens when nerves that control muscles are attacked by the immune system. It usually starts out as muscle weakness in one hand or foot.
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What Is MMN?
This is MMN
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MMN
Multifocal Motor Neuropathy (MMN)
(how to say it: muhl-tee-FOE-kuhl MOE-tur nur-AH-puh-thee)
Definition:
A rare medical disorder in which nerves that control muscles are attacked by the body's immune system.
See more glossary terms
. Before diving into the details about this rare disorder, here are some key points to keep in mind:
About 3,000 to 6,000 people in the US are thought to have MMN
- MMN is a
neurological
Neurological
(how to say it: noo-ruh-LAA-jih-kuhl)
Definition:
Having to do with the nervous system or nerves. See more glossary terms
condition that shows symptoms in adulthood (but may start sooner). - It affects one side of the body more than the other, which means it's
asymmetric
Asymmetric
(how to say it: ay-suh-MEH-truhk)
Definition:
Lack or absence of symmetry; not the same on both sides. MMN symptoms are considered asymmetric because they occur on one side of the body more than the other side. See more glossary terms
. - Symptoms often start out as weakness, cramping, and/or twitching in one hand or foot (in
distal
Distal
(how to say it: DIH-stuhl)
Definition:
Parts of the body that are located further away from the center. For example, the hand is distal to the shoulder. See more glossary terms
areas of the body).
Symptoms usually appear around the age of 40
- Motor without sensory: nerves that control muscles, called
motor neurons
Motor neurons
(how to say it: MOH-tuhr NUR-ahns)
Definition:
Nerve cells that connect to muscle tissue and control movement. See more glossary terms
, are affected by MMN. It usually does not affect
sensory neurons
Sensory neurons
(how to say it: SEN-sir-ee NUR-ahns)
Definition:
Nerve cells that make you aware of pressure, temperature (eg, if something feels too hot or cold), and pain. See more glossary terms
, though. - It can be hard to diagnose and often gets misdiagnosed.
- MMN is not life-threatening. And treatment can help slow its progression.
Learning more about MMN and its symptoms can help you prepare to talk to your doctor.
It can be difficult to zip up a jacket or coat if you have MMN.
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What causes MMN
MMN happens when your body's immune system mistakenly attacks part of your nervous system. Because it affects your nerves, MMN is considered a neurological condition.
There are several studies underway, and research is being done to learn more about this rare disease, including the root cause of MMN.
Is MMN genetic?
MMN does not appear to run in families. And there are not any specific genes that seem to be linked to MMN. So if you have MMN, that doesn't mean your children will be more likely to get it.
MMN involves "motor without sensory" neurons
In people with MMN, the immune system interferes with nerves that control your muscles, causing muscle weakness. These types of nerve cells are called motor neurons.
Although MMN affects your muscles, it usually does not cause numbness, tingling, or pain. That's because the type of nerves that make you aware of pressure, heat, cold, or pain—sensory neurons—are usually not affected by MMN.
MMN symptoms usually start out as muscle weakness in one hand or foot. As the disease progresses, its symptoms may spread to other extremities.
In MMN, symptoms occur when the immune system damages the
axon
Axon
(how to say it: AXE-on)
Definition:
The long, threadlike part of a neuron that carries impulses.
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coating of the neuron. When this happens, the nerve is no longer able to transfer signals to muscles. This is called a
conduction block
Conduction block
(how to say it: kuhn-DUCK-shin bloc)
Definition:
When a nerve impulse doesn't transmit correctly at some point along a nerve fiber.
See more glossary terms
.
Tap on the dots to learn more about what MMN looks like in the body of someone experiencing muscle weakness in their hand.
KNOW
MMN DIAGNOSIS
If you think you might have MMN, learning more about the diagnostic process can help you and your doctor connect the dots sooner.
LEARN ABOUT DIAGNOSIS
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