Multifocal Motor Neuropathy With Conduction Blocks Clinical Presentation

  • Author: Sasa Zivkovic, MD, PhD; Chief Editor: Nicholas Lorenzo, MD   more...
 
Updated: Oct 5, 2011
 

History

Typically, multifocal motor neuropathy (MMN) manifests with a slowly progressive, asymmetric, predominantly distal weakness developing over years. Weakness usually starts in a distribution of a single peripheral nerve with unilateral wrist drop, foot drop, or grip weakness. Initial involvement of the distal upper extremities is most common. Rarely, MMN may manifest with initial phrenic or cranial nerve involvement. Cramps and twitching are common, but muscle atrophy is minimal if present at all. Sensory symptoms are minimal or absent. Transient exacerbation may occur during pregnancy. As with other neuromuscular disorders, patients also commonly complain of fatigue.

Electrodiagnostic evaluation may document the presence of asymptomatic conduction blocks in other clinically unaffected nerves, and it may document more extensive involvement in patients with relatively few symptoms. Positive serology for anti-GM1 antibodies is supportive of the diagnosis of MMN, particularly higher titers.

Clinical and electrodiagnostic criteria for the diagnosis of MMN include the following[3] :

Definite MMN

Weakness without objective sensory loss in the distribution of 2 or more nerves is present for more than 1 month

Definite motor conduction block is present in at least one motor nerve with normal sensory nerve conductions

Exclusion criteria are not present.

Probable MMN

Weakness without objective sensory loss in the distribution of 2 or more nerves

The presence of probable motor conduction block in 2 or more motor nerve segments with normal sensory nerve conduction studies

Exclusion criteria are not present.

OR

Weakness without objective sensory loss in the distribution of one nerve

The presence of probable motor conduction block in one motor nerve segments with normal sensory nerve conduction studies

Exclusion criteria are not present.

At least 2 supportive criteria are met.

Supportive criteria

Elevated titers of serum IgM anti-GM1 antibodies

Increased cerebrospinal fluid (CSF) protein (< 1 g/L)

MRI shows increased signal on T2-weighted imaging of brachial plexus with diffuse nerve swelling

Objective clinical improvement following intravenous immunoglobulin (IVIG) treatment

Exclusion criteria

Upper motor neuron signs, such as spasticity, clonus, extensor plantar response

Marked bulbar involvement

Sensory involvement more marked than minor vibration loss in the lower limbs

Diffuse symmetric weakness during initial weeks

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Physical

On physical examination, the most remarkable finding is asymmetric weakness in the distribution of individual peripheral nerves that is out of proportion to muscle atrophy. Fasciculations may be present.

Cranial nerves

Cranial nerves are rarely affected, but this may be an uncommon initial manifestation of MMN. Cranial nerve involvement may be limited to the twelfth cranial nerve.

Speech is normal.

Deep tendon reflexes

Deep tendon reflexes may be absent (particularly in affected limbs) or normal. Early in the course, tendon reflexes may be brisk.

Motor strength

Asymmetric weakness may occur in a nonmyotomal pattern, usually in the distribution of individual nerves. The upper limbs, particularly the hands, are more commonly involved than the lower limbs. Weakness frequently worsens with exposure to cold.[10]

Muscles innervated by motor nerves with persistent conduction block are usually weak.

Muscle atrophy

Atrophy may be present in weak muscles, but it is usually fairly mild. Late in the disease course atrophy may be more prevalent.

Upper motor neuron signs

These signs are absent.

Muscle tone

Tone is decreased or normal. No clonus, extensor plantar response, or pseudobulbar palsy is present. Pathologic reflexes (eg, Babinski, Hoffman) are not present.

Sensory examination

Sensory examination should be normal, and the sensory loss may be suggestive of Lewis-Sumner syndrome (multifocal acquired demyelinating sensory and motor neuropathy [MADSAM]).

Coordination

Coordination is normal.

Gait

Gait is usually normal, unless more prominent involvement of lower extremity muscles occurs.

Fasciculations and cramping

These are common and may occur outside of the distribution of clinically affected nerves.

Other

No rash or gynecomastia is present.

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Causes

MMN is an autoimmune peripheral neuropathy without a known cause.

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Contributor Information and Disclosures
Author

Sasa Zivkovic, MD, PhD  Associate Professor, Department of Neurology, Division of Neuromuscular Diseases, University of Pittsburgh and VA Pittsburgh Healthcare System

Sasa Zivkovic, MD, PhD is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and Peripheral Nerve Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Paul E Barkhaus, MD  Professor, Department of Neurology, Medical College of Wisconsin; Director of Neuromuscular Diseases, Milwaukee Veterans Affairs Medical Center

Paul E Barkhaus, MD is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and American Neurological Association

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Glenn Lopate, MD  Associate Professor, Department of Neurology, Division of Neuromuscular Diseases, Washington University School of Medicine; Director of Neurology Clinic, St Louis ConnectCare; Consulting Staff, Department of Neurology, Barnes-Jewish Hospital

Glenn Lopate, MD is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and Phi Beta Kappa

Disclosure: Baxter Grant/research funds Other; Amgen Grant/research funds None

Selim R Benbadis, MD  Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, Tampa General Hospital, University of South Florida College of Medicine

Selim R Benbadis, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association

Disclosure: UCB Pharma Honoraria Speaking, consulting; Lundbeck Honoraria Speaking, consulting; Cyberonics Honoraria Speaking, consulting; Glaxo Smith Kline Honoraria Speaking, consulting; Pfizer Honoraria Speaking, consulting; Sleepmed/DigiTrace Honoraria Speaking, consulting

Chief Editor

Nicholas Lorenzo, MD  Consulting Staff, Neurology Specialists and Consultants

Nicholas Lorenzo, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Neurology, and American College of Physician Executives

Disclosure: Nothing to disclose.

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Nerve conduction studies demonstrating conduction block with temporal dispersion after proximal stimulation.
 
 
 
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