MMN is a rare, treatable, but incurable disorder of the immune system which causes muscle weakness that worsens over time. MMN commonly begins in the finger, thumb, wrist or lower leg.3,4 It affects the strength in the lower parts of the arms and hands more than the legs, usually without affecting touch sensation.1 MMN usually causes weakness in one side of the body (asymmetrical).4
While the exact cause of MMN is unknown, one potential mechanism to thought to be that immune system abnormalities affect the protective layer (myelin sheath) around nerve cells that control muscle function. The protective layer normally allows messages to be sent properly and quickly throughout the nervous system. When the protective layer breaks down (a process called demyelination), nerve damage can occur. When nerve impulses are interrupted, muscle weakness can occur.4,5
Who does MMN affect?
How is MMN diagnosed?
MMN is a rare, often difficult to diagnose disorder. Some symptoms of MMN are similar to those of other types of peripheral nerve disorders.6 The diagnosis of MMN often is based on a physical exam, an evaluation of symptoms, an electromyography (EMG) test, nerve conduction study, laboratory tests, MRI, and medical history.4,6
Your healthcare provider may also request a blood test or order other tests to fully understand your health status.4,6
What causes MMN?
While the exact cause of MMN is unknown, one potential mechanism to thought to be that immune system abnormalities affect the protective layer around nerve cells that control muscle function. In a normal nerve, the protective layer (myelin sheath) allows messages to be sent properly and quickly throughout the nervous system (Figure 1). When the protective layer (myelin sheath) breaks down (a process called demyelination), nerve damage can occur (Figure 2). When nerve impulses are interrupted, muscle weakness can occur.4,5
What else should I know about MMN?
What it is
- Chronic, treatable, but incurable immune-mediated disorder that affects nerves and muscles2
- Associated with muscle weakness affecting the hands, forearms, and lower legs that can interfere with daily living4,8
- Rare, often difficult to diagnose condition characterized by slow progressive asymmetric (on one side of the body) distal limb weakness4
What it is not
- Amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease4,6
- A nerve compression condition, such as carpal tunnel sydrome2,6
- GAMMAGARD LIQUID [Immune Globulin Infusion (Human)] 10% [Prescribing Information]. Westlake Village, CA: Baxalta US Inc.
- Katirji B, Koontz D. Disorders of peripheral nerves. In: Daroff RB, Fenichel GM, Jankovic J, Mazziotta JC, eds. Bradley's Neurology in Clinical Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2012:1915-2015.
- Slee M, Selvan A, Donaghy M. Multifocal motor neuropathy: the diagnostic spectrum and response to treatment. Neurology. 2007;69(17):1680-1687.
- Vlam L, van der Pol WL, Cats EA, et al. Multifocal motor neuropathy: diagnosis, pathogenesis and treatment strategies. Nat Rev Neurol. 2012;8(1):48-58.
- Piepers S, Jansen MD, Cats EA, van Sorge NM, van den Berg LH, van der Pol WL. IVIg inhibits classical pathway activity and anti-GM1 IgM-mediated complement deposition in MMN. J Neuroimmunol. 2010;229(1-2):256-262.
- Meuth SG, Kleinschnitz C. Multifocal motor neuropathy: update on clinical characteristics, pathophysiological concepts and therapeutic options. Eur Neurol. 2010;63(4):193-204.
- Shy ME. Peripheral neuropathies. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:2396-2409.
- Sharrack B, Hughes RA. The Guy's Neurological Disability Scale (GNDS): a new disability measure for multiple sclerosis. Mult Scler. 1999;5(4):223-233.
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