A Study On Multifocal Motor Neuropathy

Multifocal motor neuropathy is a rare type of muscle disorder that is progressive. It is an acquired neuropathy with a conduction block that is demyelinating and immune mediated.

MMN is distinguished by a slowly progressive weakness in the hand muscles, with dissimilarities in the involved muscles from the right side of the body to the left, fasciculations, and cramping, with no important sensory involvement. MMN involves the distal motor neurons of the body. It commonly affects men more than women. If detected and diagnosed early, it can be treated with a quick recovery. It is sometimes mistaken to be amyotrophic lateral sclerosis but ALS is characterized by a lack of muscle atrophy and rapid progression and is not treatable, unlike MMN.

Multifocal motor neuropathy is characterized by the frequent, mild abnormalities in the morphology of sensory fibers. There is an increase in the large caliber myelinated axons as seen in nerve biopsies. Its symptoms include muscle wasting, cramps and involuntary twitching or contractions of leg muscles. Weakness starts in a single peripheral nerve with a unilateral wrist drop, foot drop or grip weakness. The distal upper extremities are commonly involved. Diagnosis by electrodiagnostic evaluation documents the presence of asymptomatic conduction blocks. It gives high levels of anti-GM1 antibodies.

A definitive clinical picture of multifocal motor neuropathy includes the following:

1) The presence of weakness in two or more nerves, but without objective sensory loss.

2) A conduction block is present in two or more motor nerves outside the common entrapment sites.

3) The velocity of nerve conduction for sensory nerves is normal in the nerves with a motor conduction block.

4) There are no upper motor neuron signs like spasticity, clonus, extensor plantar response or pseudobulbar palsy.

To diagnose a patient with MMN, a physical examination is done. Findings should show an asymmetric weakness in the individual peripheral nerves with the possible presence of fasciculations. Cranial nerves are not often affected but in this disorder, the twelfth cranial nerve — the hypoglossal nerve — is affected, although speech is normal. There also may be an abnormality in the deep tendon reflexes of the limbs. The weakness may occur in a nonmyotomal pattern, frequently in individual nerve distribution. Muscles innervated by a persistent conduction block are frequently weak. A mild atrophy in the muscles may be present which progresses in the disease. The upper motor neuron signs are not present. Muscle tone is either decreased or normal. There is also the absence of clonus, extensor plantar response, and pseudobulbar palsy, including pathologic reflexes. Sensory findings are normal as well as coordination and gait.

Multifocal motor neuropathy does not have any known cause. For its treatment, some people don’t use any drugs since the symptoms are mild and tolerable. For others, they can be treated with intravenous immunoglobulin and immunosuppressive therapy with Cyclophosphamide.

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