Multifocal Motor Neuropathy (MMN)
MMN stands for multifocal motor neuropathy. MMN is rare and believed to be an autoimmune disorder. An autoimmune disorder develops when the immune system malfunctions and creates antibodies that attack and cause damage to a part of the body. In MMN, the myelin sheath of motor nerves is attacked. The myelin sheath is the protective covering over nerves, which aids in sending nerve signals from spine to muscles. This attack on the myelin sheath results in muscle weakness.
Symptoms of MMN
Symptoms of MMN include weakness usually beginning in a single limb, for example, the hand or the ankle. The weakness is usually different from one side of the body to the other. This weakness will interfere with and make everyday activities such as writing, holding eating utensils or walking difficult. Other symptoms frequently seen are muscle wasting, cramping and twitching.
Diagnosing MMN can be difficult for many reasons. First, because it may only affect a single nerve and cause minimal weakness in one limb, diagnosis may take a long time to make. Additionally, because it only affects motor nerves, the symptoms will initially mimic Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig's disease. Many people ultimately diagnosed with MMN are initially told they have ALS, which can be extremely frightening and stressful. Nerve conduction block may be seen in MMN, but never with ALS. Not detecting the block with a nerve conduction study can also contribute to misdiagnosis. Because MMN is an autoimmune disorder, there may be antibodies present that are detectable with a blood test. However, they may only be present in half of the people with MMN.
Diagnostic testing may include:
- Electromyography (EMG) to measure muscle activity.
- Nerve conduction studies (NCS) to measure efficiency and speed of signals of the nerves.
- Blood work to test for an anti-GM1 antibody that may be present in MMN.
The primary treatment for MMN is immune globulin. The goal of immune globulin in MMN is to stop the attack on the myelin sheath. This will then cause the symptoms to subside. Strength will increase and all of the tasks that may have become difficult will become easier. Unlike ALS, MMN is treatable. It may take one to three courses but you will note improvement with treatment. Your doctor will assess your response to therapy and determine how much immune globulin you need to maintain your response. Most people with MMN usually require long-term/lifetime therapy.
- American Academy of Neurology
- Multifocal Motor Neuropathy Information Page: National Institute of Neurological Disorders and Stroke (NINDS)
- Neuromuscular Center at Washington University
- Neuropathy Action Association
At NuFACTOR, we are committed to providing our patients all of the education, support and resources necessary to complete treatment successfully and with the desired outcomes. Please contact us with any further questions.
This content is not intended to substitute professional medical advice. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.