Multifocal motor neuropathy

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Multifocal motor neuropathy
Other namesMultifocal motor neuropathy with conduction block
Specialty Neurology

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. MMN is thought to be autoimmune. It was first described in the mid-1980s. [1]

Contents

Unlike ALS, which affects both upper and lower motor neuron pathways, MMN involves only the lower motor neuron pathway, specifically, the peripheral nerves emanating from the lower motor neurons. 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.

MMN usually involves very little pain; however, muscle cramps, spasms and twitches can cause pain for some people. MMN is not fatal, and does not diminish life expectancy. Many patients, once undergoing treatment, only experience mild symptoms over prolonged periods, though the condition remains slowly progressive. MMN can however, 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; some patients end up using aids like canes, splints 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 over long periods, often in a stepwise fashion, but unlike ALS are often treatable.[ citation needed ]

Sensory nerves are usually unaffected.[ citation needed ]

Wrist drop and foot drop (leading to trips and falls) are common symptoms. Other effects can include gradual loss of finger extension, leading to a clawlike appearance. Cold & hot temperatures exacerbate MMN symptoms to such an extent, unlike other neuropathies, that this temperature response is being investigated as a diagnostic tool. [2]

Cause

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 found at the Nodes 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, as well as a number of related gangliosides, are positive in over 80% of MMN patients. There are increasing reasons to believe these antibodies are the cause of MMN.[ citation needed ]

Diagnosis

The diagnosis of MMN depends on demonstrating that a patient has a purely motor disorder affecting individual nerves, that there are no upper motor neuron (UMN) signs, that there are no sensory deficits, and that there is evidence of conduction block. These criteria are designed to differentiate the disorder from ALS (purely motor but with UMN signs), the Lewis-Sumner Syndrome variant of Chronic inflammatory demyelinating polyneuropathy (CIDP) (similar to MMN but usually with significant sensory loss), and "vasculitis" (a type of multiple mononeuropathy syndrome caused by inflammatory damage to the blood vessels in nerves that also causes sensory and motor symptoms). [ citation needed ]

A neurologist is usually needed to determine the diagnosis, which is based on the history and physical examination along with the electrodiagnostic study, which includes nerve conduction studies (NCS) and needle electromyography (EMG). The NCS usually demonstrate conduction block. This can be done by showing that the nerve signal cannot conduct past a "lesion" at some point along the nerve. For example, if the nerve is blocked in the forearm, an electrical impulse can easily get from the wrist to the hand if the stimulus is placed at the wrist. However, the signal will be blocked from reaching the hand if the stimulus is applied at the elbow. In MMN, sensory conduction along the same path should be normal. The EMG portion of the test looks for signals in the way muscles fire. In MMN it will most likely reveal abnormalities suggesting that some percentage of the motor axons has been damaged. Laboratory testing for GM1 antibodies is frequently done, and can be very helpful if they are abnormal. However, since only a third of patients with MMN have these antibodies, a negative test does not rule out the disorder. Spinal fluid examination is not usually helpful.[ citation needed ]

Treatment

Multifocal motor neuropathy is normally treated by receiving intravenous immunoglobulin (IVIG), which can in many cases be highly effective, or immunosuppressive therapy with cyclophosphamide or rituximab. Steroid treatment (prednisone) and plasmapheresis are no longer considered to be useful treatments(not usually some pt highly recommended); [3] 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. [4]

Related Research Articles

Motor neuron disease Group of neurological disorders affecting motor neurons

Motor neuron diseases or motor neurone diseases (MNDs) are a group of rare neurodegenerative disorders that selectively affect motor neurons, the cells which control voluntary muscles of the body. They include amyotrophic lateral sclerosis (ALS), progressive bulbar palsy (PBP), pseudobulbar palsy, progressive muscular atrophy (PMA), primary lateral sclerosis (PLS), spinal muscular atrophy (SMA) and monomelic amyotrophy (MMA), as well as some rarer variants resembling ALS.

Lambert–Eaton myasthenic syndrome Medical condition

Lambert–Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder characterized by muscle weakness of the limbs.

Neuromyotonia (NMT) is a form of peripheral nerve hyperexcitability that causes spontaneous muscular activity resulting from repetitive motor unit action potentials of peripheral origin. NMT along with Morvan's syndrome are the most severe types in the Peripheral Nerve Hyperexciteability spectrum. Example of two more common and less severe syndromes in the spectrum are Cramp Fasciculation Syndrome and Benign Fasciculation Syndrome. NMT can have both hereditary and acquired forms. The prevalence of NMT is unknown.

Benign fasciculation syndrome Medical condition

Benign fasciculation syndrome (BFS) is characterized by fasciculation (twitching) of voluntary muscles in the body. The twitching can occur in any voluntary muscle group but is most common in the eyelids, arms, hands, fingers, legs, and feet. The tongue can also be affected. The twitching may be occasional to continuous. BFS must be distinguished from other conditions that include muscle twitches.

Polyneuropathy Medical condition

Polyneuropathy is damage or disease affecting peripheral nerves in roughly the same areas on both sides of the body, featuring weakness, numbness, and burning pain. It usually begins in the hands and feet and may progress to the arms and legs and sometimes to other parts of the body where it may affect the autonomic nervous system. It may be acute or chronic. A number of different disorders may cause polyneuropathy, including diabetes and some types of Guillain–Barré syndrome.

Alcoholic polyneuropathy Medical condition

Alcoholic polyneuropathy is a neurological disorder in which peripheral nerves throughout the body malfunction simultaneously. It is defined by axonal degeneration in neurons of both the sensory and motor systems and initially occurs at the distal ends of the longest axons in the body. This nerve damage causes an individual to experience pain and motor weakness, first in the feet and hands and then progressing centrally. Alcoholic polyneuropathy is caused primarily by chronic alcoholism; however, vitamin deficiencies are also known to contribute to its development. This disease typically occurs in chronic alcoholics who have some sort of nutritional deficiency. Treatment may involve nutritional supplementation, pain management, and abstaining from alcohol.

Nerve conduction study Diagnostic test for nerve function

A nerve conduction study (NCS) is a medical diagnostic test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body. These tests may be performed by medical specialists such as clinical neurophysiologists, physical therapists, chiropractors, physiatrists, and neurologists who subspecialize in electrodiagnostic medicine. In the United States, neurologists and physiatrists receive training in electrodiagnostic medicine as part of residency training and in some cases acquire additional expertise during a fellowship in clinical neurophysiology, electrodiagnostic medicine, or neuromuscular medicine. Outside the US, clinical neurophysiologists learn needle EMG and NCS testing.

Neuritis Inflammation of a nerve or generally any part of the nervous system

Neuritis is inflammation of a nerve or the general inflammation of the peripheral nervous system. Inflammation, and frequently concomitant demyelination, cause impaired transmission of neural signals and leads to aberrant nerve function. Neuritis is often conflated with neuropathy, a broad term describing any disease process which affects the peripheral nervous system. However, neuropathies may be due to either inflammatory or non-inflammatory causes, and the term encompasses any form of damage, degeneration, or dysfunction, while neuritis refers specifically to the inflammatory process.

Nerve conduction velocity Speed at which an electrochemical impulse propagates down a neural pathway

In neuroscience, nerve conduction velocity (CV) is an important aspect of nerve conduction studies. It is the speed at which an electrochemical impulse propagates down a neural pathway. Conduction velocities are affected by a wide array of factors, which include; age, sex, and various medical conditions. Studies allow for better diagnoses of various neuropathies, especially demyelinating diseases as these conditions result in reduced or non-existent conduction velocities.

Chronic inflammatory demyelinating polyneuropathy Medical condition

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an acquired autoimmune disease of the peripheral nervous system characterized by progressive weakness and impaired sensory function in the legs and arms. The disorder is sometimes called chronic relapsing polyneuropathy (CRP) or chronic inflammatory demyelinating polyradiculoneuropathy. CIDP is closely related to Guillain–Barré syndrome and it is considered the chronic counterpart of that acute disease. Its symptoms are also similar to progressive inflammatory neuropathy. It is one of several types of neuropathy.

Rheobase

Rheobase is a measure of membrane potential excitability. In neuroscience, rheobase is the minimal current amplitude of infinite duration that results in the depolarization threshold of the cell membranes being reached, such as an action potential or the contraction of a muscle. In Greek, the root rhe translates to "current or flow", and basi means "bottom or foundation": thus the rheobase is the minimum current that will produce an action potential or muscle contraction.

Progressive bulbar palsy (PBP) is a medical condition. It belongs to a group of disorders known as motor neuron diseases. PBP is a disease that attacks the nerves supplying the bulbar muscles. These disorders are characterized by the degeneration of motor neurons in the cerebral cortex, spinal cord, brain stem, and pyramidal tracts. This specifically involves the glossopharyngeal nerve (IX), vagus nerve (X), and hypoglossal nerve (XII).

Guillain–Barré syndrome (GBS) is a rapid-onset muscle weakness caused by the immune system damaging the peripheral nervous system. Typically, both sides of the body are involved, and the initial symptoms are changes in sensation or pain often in the back along with muscle weakness, beginning in the feet and hands, often spreading to the arms and upper body. The symptoms may develop over hours to a few weeks. During the acute phase, the disorder can be life-threatening, with about 15% of people developing weakness of the breathing muscles and, therefore, requiring mechanical ventilation. Some are affected by changes in the function of the autonomic nervous system, which can lead to dangerous abnormalities in heart rate and blood pressure.

Acute motor axonal neuropathy (AMAN) is a variant of Guillain–Barré syndrome. It is characterized by acute paralysis and loss of reflexes without sensory loss. Pathologically, there is motor axonal degeneration with antibody-mediated attacks of motor nerves and nodes of Ranvier.

Antiganglioside antibodies that react to self-gangliosides are found in autoimmune neuropathies. These antibodies were first found to react with cerebellar cells. These antibodies show highest association with certain forms of Guillain–Barré syndrome.

Hereditary motor and sensory neuropathy Medical condition

Hereditary motor and sensory neuropathies (HMSN) is a name sometimes given to a group of different neuropathies which are all characterized by their impact upon both afferent and efferent neural communication. HMSN are characterised by atypical neural development and degradation of neural tissue. The two common forms of HMSN are either hypertrophic demyelinated nerves or complete atrophy of neural tissue. Hypertrophic condition causes neural stiffness and a demyelination of nerves in the peripheral nervous system, and atrophy causes the breakdown of axons and neural cell bodies. In these disorders, a patient experiences progressive muscle atrophy and sensory neuropathy of the extremities.

Anti-MAG peripheral neuropathy is a specific type of peripheral neuropathy in which the person's own immune system attacks cells that are specific in maintaining a healthy nervous system. As these cells are destroyed by antibodies, the nerve cells in the surrounding region begin to lose function and create many problems in both sensory and motor function. Specifically, antibodies against myelin-associated glycoprotein (MAG) damage Schwann cells. While the disorder occurs in only 10% of those afflicted with peripheral neuropathy, people afflicted have symptoms such as muscle weakness, sensory problems, and other motor deficits usually starting in the form of a tremor of the hands or trouble walking. There are, however, multiple treatments that range from simple exercises in order to build strength to targeted drug treatments that have been shown to improve function in people with this type of peripheral neuropathy.

Monomelic amyotrophy Medical condition

Monomelic amyotrophy (MMA) is a rare motor neuron disease first described in 1959 in Japan. Its symptoms usually appear about two years after adolescent growth spurt and is significantly more common in males, with an average age of onset between 15 and 25 years. MMA is reported most frequently in Asia but has a global distribution. It is typically marked by insidious onset of muscle atrophy of an upper limb, which plateaus after two to five years from which it neither improves nor worsens. There is no pain or sensory loss associated with MMA. MMA is not believed to be hereditary.

Peripheral mononeuropathy is a nerve related disease where a single nerve, that is used to transport messages from the brain to the peripheral body, is diseased or damaged. Peripheral neuropathy is a general term that indicates any disorder of the peripheral nervous system. The name of the disorder itself can be broken down in order to understand this better; peripheral: in regard to peripheral neuropathy, refers to outside of the brain and spinal cord; neuro: means nerve related; -pathy; means disease. Peripheral mononeuropathy is a disorder that links to Peripheral Neuropathy, as it only effects a single peripheral nerve rather than several damaged or diseased nerves throughout the body. Healthy peripheral nerves are able to “carry messages from the brain and spinal cord to muscles, organs, and other body tissues”.

Femoral nerve dysfunction, also known as femoral neuropathy, is a rare type of peripheral nervous system disorder that arises from damage to nerves, specifically the femoral nerve. Given the location of the femoral nerve, indications of dysfunction are centered around the lack of mobility and sensation in lower parts of the legs. The causes of such neuropathy can stem from both direct and indirect injuries, pressures and diseases. Physical examinations are usually first carried out, depending on the high severity of the injury. In the cases of patients with hemorrhage, imaging techniques are used before any physical examination. Another diagnostic method, electrodiagnostic studies, are recognized as the gold standard that is used to confirm the injury of the femoral nerve. After diagnosis, different treatment methods are provided to the patients depending upon their symptoms in order to effectively target the underlying causes. Currently, femoral neuropathy is highly underdiagnosed and its precedent medical history is not well documented worldwide.

References

  1. ↑ Roth, G; Rohr J; Magistris MR; Ochsner F (1986). "Motor neuropathy with proximal multifocal persistent conduction block, fasciculations and myokymia. Evolution to tetraplegia". Eur Neurol. 25 (6): 416–423. doi:10.1159/000116045. PMID   3024989.
  2. ↑ Straver DC, van Asseldonk JT, Notermans NC, Wokke JH, van den Berg LH, Franssen H (February 2011). "Cold paresis in multifocal motor neuropathy". J Neurol. 258 (2): 212–217. doi:10.1007/s00415-010-5712-3. PMC   3036831 . PMID   20803025.
  3. ↑ Chaudhry, V (2004). "Multifocal motor neuropathy: response to human immune globulin". Annals of Neurology. 33 (3): 237–42. doi:10.1002/ana.410330303. PMID   8498806. S2CID   20532905.
  4. ↑ Harbo T, Andersen H, Hess A, Hansen K, Sindrup SH, Jakobsen J (2009). "Subcutaneous versus intravenous immunoglobulin in multifocal motor neuropathy: a randomized, single-blinded cross-over trial". Eur. J. Neurol. 16 (5): 631–8. doi:10.1111/j.1468-1331.2009.02568.x. PMID   19236457. S2CID   20624972.
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