Multifocal Motor Neuropathy

Multifocal Motor Neuropathy (MMN) is a rare condition in which multiple motor nerves are attacked by one’s immune system. This causes weakness without loss of sensation. The disorder affects less than one person per 100,000 people. Men are almost twice as likely as women to develop the illness and most people contract the disease between the ages of 35 and 70. The specific nature of the attack is unique and puzzling, since motor and sensory fibers are intermingled within the nerve trunks of the arms and legs, but only the motor nerves become involved.

With very rare exceptions, MMN does not shorten life, or cause major problems with breathing or swallowing. However, it can cause a great deal of dysfunction and disability and the disorder appears to persist indefinitely and rarely goes into a long-term remission. The disorder is sometimes mistaken for amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease) but unlike ALS, it is treatable. An early and accurate diagnosis allows patients to recover quickly.

MMN is thought to be caused by alterations in the immune system, such that certain proteins (antibodies) that would normally protect one from viruses and bacteria begin to attack constituents of peripheral nerves. Antibodies may be directed against “GM-1,” a ganglioside located at the Node of Ranvier. These antibodies have been detected in at least one third of MMN patients. More recent studies also suggest that newer tests for antibodies directed against GM-1 combined with a number of related gangliosides, are positive in over 80% of MMN patients. Thus, there are increasing reasons to believe these antibodies are the cause of MMN.