RESEARCH: Pain/Neuropathy

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Neurophysiol Clin 2000 Feb;30(1):27-42

Neurophysiological studies of thin myelinated (A delta) and unmyelinated ©

fibers: application to peripheral neuropathies.

Santiago S, Ferrer T, Espinosa ML.

Department of Neurophysiology, La Paz General Hospital, Madrid, Spain.

Dysfunction of small fibers may appear in isolation or associated with large

fiber lesions. In some acute neuropathies, such as pandysautonomia,

small-fiber impairment is relatively pure but it may also appear in

disorders with prominent somatic damage, such as Guillain-Barre syndrome, in

which autonomic failure worsens the prognosis. At the present time, chronic

idiopathic distal small-fiber neuropathy is diagnosed more frequently, and

in some prevalent disorders, such as diabetic or amyloidotic

polyneuropathies, small-fiber dysfunction is very noticeable. In pure

autonomic failure, a peripheral autonomic failure exists, distinguishing it

from multiple-system atrophy. Complex regional pain syndrome is a severe

condition in which small fibers are responsible for disabling signs and

symptoms, and only instrumental recordings lead to the proper treatment.

Standard neurophysiological techniques evaluate large myelinated fibers

exclusively. Small-fiber polyneuropathy has been considered as a type of

somatic neuropathy, but thin myelinated and unmyelinated fibers are

responsible not only for temperature and pain perception but also autonomic

function. For instance, full autonomic evaluation is needed in some clinical

situations such as autonomic failure in the elderly or orthostatic

intolerance syndrome. To evaluate small-fiber impairment we need a battery

of sensitive, reproducible, specific and noninvasive tests covering somatic

and autonomic systems. In this review, we describe and analyze a number of

neurophysiological techniques used to diagnose and characterize small-fiber

dysfunction in humans. These include cardiovascular monitoring, sudomotor

testing, pupillary responses and quantitative sensory tests, and also to

some extent thermography and laser evoked potentials. The use of such

techniques has proven useful not only for diagnosis, but also to guide

adequate therapy and optimize follow-up.

Publication Types:

Review

Review, Tutorial

PMID: 10740794 [PubMed - indexed for MEDLINE]