Multifocal motor neuropathy
Encyclopedia
Multifocal motor neuropathy (MMN) is a progressively worsening condition where muscles in the extremities gradually weaken. The disorder, a pure motor neuropathy syndrome, is sometimes mistaken for amyotrophic lateral sclerosis
(ALS) because of the similarity in the clinical picture, especially if muscle fasciculations are present. Unlike ALS, MMN is usually asymmetric. MMN is thought to be autoimmune. It was first described in the mid-1980s.
Unlike ALS which affects both upper and lower motor nerves, MMN involves only lower motor nerves. Nevertheless, definitive diagnosis is often difficult, and many MMN patients labor for months or years under an ALS diagnosis before finally getting a determination of MMN.
While MMN usually involves no pain (except for muscle cramps) and is rarely fatal, it can lead to significant disability, with loss of function in hands affecting ability to work and perform everyday tasks, and foot drop
leading to inability to stand and walk; many patients end up using aids like canes and walkers.
Sensory nerves are usually unaffected.
Wrist drop and foot drop (leading to difficulty walking) are common symptoms. Other effects can include gradual loss of finger extension, leading to a clawlike appearance. Cold exacerbates MMN symptoms to such an extent, unlike other neuropathies, that it is being investigated as a diagnostic tool.
(IVIG) or immunosuppressive therapy with cyclophosphamide
or rituximab
. Steroid
treatment (prednisone
) and plasmapheresis
are no longer considered to be useful treatments ; prednisone can exacerbate symptoms. IVIg is the primary treatment, with about 80% of patients responding, usually requiring regular infusions at intervals of 1 week to several months. Other treatments are considered in case of lack of response to IVIg, or sometimes because of the high cost of immunoglobulin. Subcutaneous immunoglobulin is under study as a less invasive, more-convenient alternative to IV delivery .
Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis , also referred to as Lou Gehrig's disease, is a form of motor neuron disease caused by the degeneration of upper and lower neurons, located in the ventral horn of the spinal cord and the cortical neurons that provide their efferent input...
(ALS) because of the similarity in the clinical picture, especially if muscle fasciculations are present. Unlike ALS, MMN is usually asymmetric. MMN is thought to be autoimmune. It was first described in the mid-1980s.
Unlike ALS which affects both upper and lower motor nerves, MMN involves only lower motor nerves. Nevertheless, definitive diagnosis is often difficult, and many MMN patients labor for months or years under an ALS diagnosis before finally getting a determination of MMN.
While MMN usually involves no pain (except for muscle cramps) and is rarely fatal, it can lead to significant disability, with loss of function in hands affecting ability to work and perform everyday tasks, and foot drop
Foot drop
Foot drop is the dropping of the forefoot due to weakness, damage to the peroneal nerve or paralysis of the muscles in the anterior portion of the lower leg. It is usually a symptom of a greater problem, not a disease in itself. It is characterized by the inability or difficulty in moving the ankle...
leading to inability to stand and walk; many patients end up using aids like canes and walkers.
Symptoms
Usually beginning in one or both hands, MMN is characterized by weakness, muscle atrophy, cramping, and often profuse fasciculations (muscle twitching). The symptoms are progressive, often in a stepwise fashion, but unlike ALS are often treatable.Sensory nerves are usually unaffected.
Wrist drop and foot drop (leading to difficulty walking) are common symptoms. Other effects can include gradual loss of finger extension, leading to a clawlike appearance. Cold exacerbates MMN symptoms to such an extent, unlike other neuropathies, that it is being investigated as a diagnostic tool.
Treatment
Although no treatment is required in some cases, multifocal motor neuropathy is normally treated by receiving intravenous immunoglobulinIntravenous immunoglobulin
Intravenous immunoglobulin is a blood product administered intravenously. It contains the pooled IgG extracted from the plasma of over one thousand blood donors. IVIG's effects last between 2 weeks and 3 months...
(IVIG) or immunosuppressive therapy with cyclophosphamide
Cyclophosphamide
Cyclophosphamide , also known as cytophosphane, is a nitrogen mustard alkylating agent, from the oxazophorines group....
or rituximab
Rituximab
Rituximab, sold under the trade names Rituxan and MabThera, is a chimeric monoclonal antibody against the protein CD20, which is primarily found on the surface of B cells...
. Steroid
Steroid
A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...
treatment (prednisone
Prednisone
Prednisone is a synthetic corticosteroid drug that is particularly effective as an immunosuppressant drug. It is used to treat certain inflammatory diseases and some types of cancer, but has significant adverse effects...
) and plasmapheresis
Plasmapheresis
Plasmapheresis is the removal, treatment, and return of blood plasma from blood circulation. It is thus an extracorporeal therapy...
are no longer considered to be useful treatments ; prednisone can exacerbate symptoms. IVIg is the primary treatment, with about 80% of patients responding, usually requiring regular infusions at intervals of 1 week to several months. Other treatments are considered in case of lack of response to IVIg, or sometimes because of the high cost of immunoglobulin. Subcutaneous immunoglobulin is under study as a less invasive, more-convenient alternative to IV delivery .