MMN
MMN — Multifocal Motor Neuropathy
A rare disease affecting motor nerves
Multifocal Motor Neuropathy (MMN) is a rare disorder of the peripheral nerves that primarily affects adults, most commonly between the ages of 20 and 50. It occurs more frequently in men than in women.
What is Multifocal Motor Neuropathy (MMN)?
Multifocal Motor Neuropathy (MMN) is a chronic neurological disorder that affects motor nerves, which control muscle movement. It is characterized by slowly progressive muscle weakness, most commonly in the hands and arms, although other areas may also be affected.
Unlike some other neuropathies, MMN does not significantly affect sensation — feeling is usually preserved, which is an important distinction compared to CIDP.
Weakness is often asymmetric (affecting one side more than the other) and may worsen over time if left untreated.
The prevalence of MMN is low, estimated at around 1–2 cases per 100,000 people.
What causes MMN?
MMN is believed to be an immune-mediated disorder in which the body’s immune system mistakenly attacks parts of the peripheral nerves.
In many patients, antibodies target nerve components, leading to disruption in nerve signal transmission. Unlike CIDP, MMN is typically associated with conduction block rather than widespread demyelination.
This means that electrical signals cannot properly travel along the nerve to the muscle, resulting in weakness.
The exact cause of MMN remains unknown.
How is MMN diagnosed?
Diagnosis of MMN is based on clinical features and diagnostic testing:
Symptoms:
progressive muscle weakness, especially in hands and forearms
asymmetric weakness
muscle cramps and twitching (fasciculations)
preserved sensation
Tests:
nerve conduction studies (show conduction block)
EMG
blood tests (may detect specific antibodies)
exclusion of other neurological conditions
How is MMN treated?
The main treatment for MMN is:
Intravenous Immunoglobulin (IVIG)
IVIG is the most effective and commonly used therapy for MMN. It improves muscle strength in most patients and helps slow disease progression. Treatment is typically given at regular intervals.
Unlike CIDP, corticosteroids and plasma exchange are generally not effective in MMN and may even worsen symptoms.
Subcutaneous Immunoglobulin (SCIg)
In some patients, SCIg may be used as an alternative, allowing for home-based treatment.
If left untreated, MMN may lead to progressive weakness and functional disability. However, with appropriate therapy, many patients can maintain a good quality of life over the long term.