Characterizing
Diabetic Neuropathy
In 1995, an estimated 135 million people worldwide had diabetes,
of which 25% will develop foot problems related to the disease,
i.e., diabetic neuropathy. The World Health Organization (WHO)
estimates the number of diabetes will reach 300 million by 2025.
Four to five percent of health budgets are spent on
diabetes-related illnesses, such as the management of diabetic
neuropathy and its consequences. This neuropathy often causes
severe pain and can be incapacitating. The medoc
TSA-II NeuroSensory Analyzer and the VSA-3000 Vibratory Sensory
Analyzer enable quantitative evaluation of the integrity of both
small and large-caliber sensory nerve fibers.
Nerve Fiber Types
Nerves consist of fibers of variable diameter with the thicker
fibers having a faster conduction velocity. Three types of fibers
are generally recognized in the sensory subclass of nerve fibers:
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A-beta fibers, the largest
fibers, mediate the sensations of touch and mild pressure,
as well as the sensation of position of joints and
vibration, at a conduction velocity above 30 m/sec. |
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A-delta fibers, smaller than
A-beta fibers, mediate the sensation of cold and the first
components of the sensation of pain, at a conduction
velocity between 2 and 30 m/sec. |
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C fibers, the slowest and
smallest, mediate the sensation of warmth and the main
component of the sensation of pain, at a conduction
velocity less than 2 m/sec. In addition, C fibers subserve
most of the autonomic peripheral functions. |
Testing Nerve Fibers
Traditional tests such as EMG and Nerve Conduction Velocity are
not able to test the function of the small fibers; yet
small-caliber fibers (i.e., A-delta & C-fibers) constitute 70%
of the peripheral nerve system, with C and A-delta fibers
responsible for pain transmission. Several disease processes,
including diabetic neuropathy, afflict the peripheral nerves,
typically both small and large fibers, though this can be at
different intervals. Several authors have described findings
showing that quantitative assessment of thermal sensitivity
(small-fiber testing) may be of value in the detection of early
diabetic neuropathy, even in patients without symptoms or signs of
a clinical neuropathy. Others have argued that vibratory and
thermal testing should be a primary screening test for diabetic
peripheral neuropathy. Vibratory thresholds (large, A-beta fiber
testing) have been described as an effective predictor of the risk
of foot ulceration in diabetes. The 1992 Consensus Statement from
the San Antonion Conference on Diabetic Neuropathy (as published
in NEUROLOGY, 1992; 42:1823-1839) recommended the use of
Quantitative Sensory Testing (QST).
Uremic Neuropathy
Peripheral neuropathy is found in most renal patients. In fact,
polyneuropathy is one of the most common consequences of chronic
renal failure (Lindblom & Tegner, 1985; Weseley et al, 1989).
The majority of these patients are asymptomatic, requiring
electrophysiological testing to confirm abnormality. The health of
the peripheral nerve is recognized as an important, quantitative
serial or longitudinal measure for effectiveness of dialysis.
Nielson (1973) described the impairment of vibratory function in
these patients. Lindblom & Tegner (1975) and Angus-Leppan
& Burke (1992) reported high incidence of vibratory sensory
pathology.
TSA-II NeuroSensory Analyzer
Indicates Neuropathy in the Uremic Patient
Abnormal thermal sensory thresholds (i.e., small-fiber
impairment), as identified by the TSA-II NeuroSensory Analyzer,
have recently been cited as an early indicator or first sign of
neuropathy in the uremic patient (Yosipovitch et al, 1995). |
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