Multifocal Motor Neuropathy
What is MMN?Multifocal Motor Neuropathy (MMN) is a rare disorder in which focal areas of multiple motor nerves are attacked by one’s own immune system. Typically, MMN is slowly progressive, resulting in asymmetrical weakness of a patient’s limbs. Patients frequently develop weakness in their hand(s), resulting in dropping of objects or sometimes inability to turn a key in a lock. The weakness associated with MMN can be recognized as fitting a specific nerve territory.
Who is impacted?The prevalence of this very rare disease is estimated to be 0.6 cases in every 100,000 people, which makes it even more rare than Guillain-Barre Syndrome, a spontaneously self-limiting disorder in which 1-2/100,000 cases occur each year in North America and Europe.
How is MMN diagnosed?The diagnosis of MMN is a clinical one which depends on demonstrating that the patient:
- Has a purely motor disorder affecting individual nerves
- Does not have UMN (upper motor neuron) signs such as brisk reflexes at the knees or ankles or spasticity in the limbs
- Has no difficulty speaking or swallowing
- Has no sensory deficits
- Has evidence of focal areas of nerve in which electrical impulses are slowed or blocked (conduction block) which can be detected on electrophysiology tests