Physiological approach to peripheral neuropathy. Conventional nerve conduction studies and magnetic motor root stimulation]

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Physiological approach to peripheral neuropathy. Conventional nerve conduction

studies and magnetic motor root stimulation

(Abstract below; original article in Japanese)

Rinsho Shinkeigaku. 2004 Nov;44(11):986-90

Ugawa Y.

Department of Neurology, Division of Neuroscience, Graduate School of Medicine,

University of Tokyo.

In this communication, I first show some points we should mind in the

conventional peripheral nerve conduction studies and later present clinical

usefulness of motor root stimulation for peripheral neuropathy.

CONVENTIONAL NERVE CONDUCTION STUDIES (NCS): The most important point revealed

by the conventional NCSs is whether neuropathy is due to axonal degeneration or

demyelinating process. Precise clinical examination with this neurophysiological

information leads us to a diagnosis and treatment. Poor clinical examination

makes these findings useless. Long standing axonal degeneration sometimes

induces secondary demyelination at the most distal part of involved nerves. On

the other hand, severe segmental demyelination often provokes secondary axonal

degeneration at distal parts to the site of demyelination. These secondary

changes show the same abnormal neurophysiological findings as those of the

primary involvement. We should be careful of this possibility when interpreting

the results of NCS. NCS of sensory nerves is not good at revealing demyelinating

process. Mild temporal dispersion of potentials often reduces an amplitude of

SNAP or loss of responses, which usually suggests axonal degeneration, because

of short duration of sensory nerve potentials.

MOTOR ROOT STIMULATION IN PERIPHERAL NEUROPATHY: Magnetic stimulation with a

coil placed over the spine activates motor roots and evokes EMG responses from

upper and lower limb muscles. The site of activation with this method was

determined to be where the motor roots exit from the spinal canal

(intervertebral foramina) (J Neurol Neurosurg Psychiatry 52 (9): 1025-1032,

1989) because induced currents are very dense at such a foramen made by electric

resistant bones. In several kinds of peripheral neuropathy, this method has been

used to detect a lesion at a proximal part of the peripheral nerves which can

not be detected by the conventional NCSs. I present a few cases in whom motor

root stimulation had a clinical merit. In a patient with neuralgic amyotrophy,

motor root stimulation disclosed a conduction block between the cervical

intervertebral foramen and brachial plexus which was not detected by

conventional NCSs. Motor root stimulation clearly revealed demyelination in a

patient with CIDP in whom sural nerve biopsy findings suggested axonal

degeneration, that must be secondary to demyelination. In a patient with

tomacular neuropathy, magnetic stimulation revealed conduction delay in the

spinal nerve within the spinal canal (Clin Neurol (Jap), 28: 447-452, 1988).

Based on the above results, combination of NCSs and magnetic motor root

stimulation must brush up the neurophysiological approach to peripheral

neuropathy.

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