What is the role of EMG and NCV in the workup of toxic neuropathy?

Updated: Dec 06, 2017
  • Author: Jonathan S Rutchik, MD, MPH, FACOEM; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
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Answer

Electromyography (EMG) and nerve conduction study (NCV)

  • Using EMG and NCV, peripheral neuropathy may be separated into axonal and demyelinating forms.

  • Axonal neuropathies are more commonly the result of chronic low-level occupational or environmental toxicity.

  • Axonal neuropathies are characterized by sensory amplitude loss in the lower extremities, commonly the sural and or superficial peroneal nerves.

  • More severe axonal neuropathies may involve motor fibers and thus motor amplitudes may be small.

  • When motor fibers are involved, then fibrillation may be noted as evidence for acute denervation. For more chronic neuropathies, polyphasia and wave forms for large and long duration are evident. EMG needle assessment may then help classify duration of the neuropathy.

  • Demyelination-type neuropathies are characterized by sensory and motor slowing.

  • Some toxic neuropathies that are the result of high-level acute exposure may result in severe motor demyelinating neuropathies. However, these conditions are rare. “Ginger Jack leg” paralysis from ingestion of organophosphates is one example of this. NCV may reveal prolonged F waves initially, but then later, motor slowing.

  • EMG needle testing in these cases may be normal if the condition is purely demyelinating.

  • Characterizing a neuropathy into demyelinating or axonal may assist in identifying chemical agents responsible. (See Table 6.)

  • The differential diagnosis, however, must include inherited neuropathies as well as other common acquired neuropathies.

  • Patients with inherited demyelinating neuropathies are noted to have prolonged and symmetrical sensory and/or motor nerve conduction velocities.

  • Those with inherited axonal neuropathies may have small amplitudes that are out of proportion to their relatively minor sensory or motor findings.

  • These patients may also have high arches or other congenital physical ailments.

  • Patients with other acquired neuropathies, such as diabetes or thyroiditis, may have EMG and NCV findings that are inseparable from those with toxic neuropathy.

Table 6. Industrial Agents and Pharmaceuticals Associated With Peripheral Neuropathy (Open Table in a new window)

Almitrine (s)

“Spanish toxic oil”

Arsenic (s)(d)

2-t-Butylazo- 2- hydroxyl- 5 methylhexane

Capsaicin

Acrylamide

Carbamate pesticides (nm)

Allyl chloride

Carbon disulfide (m)(d)

Amiodaron e (d)

Chloramphenicol (s)

Amitriptyline

Cimetidine (m)

Carbamates (nm)

Cisplatin (s)

Carbon monoxide

Cyanate

Chloroquine

Cycloleucine

Colchicine

Cytarabine

Dichloroacetic acid

Dapsone (m)

Disulfiram (m)

Dichloroacetylene (cr)

Ethionamide

Didoxynucleosides (s) (ddC, ddI, d4T)

Ethyl alcohol

Dimethylaminopropionitrile

Ethylene glycol (cr)

Doxorubicin (m)

Ethylene oxide

Ethambutol (s)

Germanium dioxide

Etoposide (s)

Gold

Glutethimide

Hexamethylmelamine

Hexachlorophene

Hydrazine

Hydralazine (s)

Indomethacin

Hyperinsulinemia/ hypoglycemia (m)

Isoniazid

Imipramine (m)

Lincomycin (nm)

Interferon alpha (nm)

Lithium

Lead (m)

L-Tryptophan

Lidocaine

Mercury, inorganic

Methyl n-butyl ketone (m)(d)

Mercury, organic

Metronidazole (s)

Methaqualone

Misonidazole (s)

Methyl bromide

Muzolimine

Methyl methacrylate

Nitrous Oxide (s)

N hexane (d)

Organophosphates (m)

Naproxen

Organophosphorus compounds (nm)

Nitrofurantoin (m)

Polychlorinated biphenyls (s)

Penicillamine (nm)

Polymyxin (nm)

Perhexiline (d)

Pyrethroids (ic)

Phenol

Pyridoxine (s)

Phenytoin

Sarin

Pyriminil

Succinylcholine (nm)

Quinine (nm)

Sulfonamides (m), sulfasalazine

Statins

Tacrolimus

Stilbamidine (cr)

Taxanes (paclitaxel, docetaxel) (s)

Suramin

Thalidomide (s)

Tetrachloroethane

Thallium (s)

Tetracyclines (nm)

Trimethaphan (nm)

Trithiozine

Vidarabine

Tubocurarine (nm)

Vincristine (m)

Vincristine  (m), Vinca alkaloids

Zimeldine

Vinyl chloride

(s): Predominantly sensory

(m): Predominantly motor

(d): Possibly demyelination with conduction block

(cr): Associated with cranial neuropathy

(nm): Associated with neuromuscular transmission syndromes

(ic): Associated with axon ion channel syndromes

Bold: A rating for common or strong association

Unbolded: B rating for less common or less than strong association 


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