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

[neuralgic amyotrophy]

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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neuralgic amyotrophy

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