A portable system for measuring cutaneous thresholds for warming and cooling.

Abstract

SUMMARY Measurement of cutaneous thermal thresholds is a valuable technique for detecting small fibre neuropathy. A robust and portable microcomputer controlled system, which separately measures thresholds for warming and cooling, is described. Thresholds at three sites have been measured; the cheek, the dorsum of the hand and the sole of the foot. Regional variability and a correlation with age have been found, indicating the sensitivity of this system. Psychophysical estimates of cutaneous thresholds for thermal sensation are now recognised as a valuable means of assessing small nerve fibre function.'-5 In mammalian peripheral nerve, small (0-5-6p diameter) myelinated and unmyelinated nerve fibres are four times more numerous than the large (7-13 p diameter) myelinated fibres.6 Disease of these small fibres is common in diabetes7 8 and is also a feature of some painful neuropathies,9 but stimulation and direct measurement of electrical responses in them is not possible under clinical conditions. Nerve conduction studies are therefore of limited diagnostic value in small fibre disease. Since cutaneous thermal sensations of cold are conveyed in the small myelinated fibres and sensations of warmth in the unmyelinated fibres,'0 the integrity of each of these nerve fibre groups may be tested by psychophysical estimates of thresholds for thermal sensation.Pure thermal stimuli can be conveniently given by means of thermoelectric modules in contact with the skin. First introduced in a device for physiological research, " a thermoelectric module was then incorporated in the clinically used "Marstock" thermal testing system.' In 1978 Dyck et al2 described a computer assisted method for measuring thresholds for cooling with a thermoelectric module, which measured both the temperature change and the amount of heat exchange the subject detects. The ingenious psychophysical testing routines and design concepts for computer controlled sensory testing devices introduced by those authors, have greatly influenced subsequent workers.We describe a system which can measure thresholds for both warming and cooling. The testing routine employed is quick and easily performed by untrained subjects. Following each dynamic ramp of temperature change, spontaneous thermal reequilibration occurs, so that it has been possible to exclude the water cooling arrangements which other designs have incorporated.'" Thus our system has been made simple and portable.We present here our results from a series of control subjects tested for both sensory modalities at three sites, the face, hand and foot.Method

Thermosensory threshold: a sensitive test of HIV associated peripheral neuropathy?

“…Winer et al (1992) found the upper limits of the temperature threshold of the foot to be lower than in our study (e.g. warm sensation up to 1.08C for normal controls and 8.08C for those with neuropathy), which may re¯ect differences in methodology, since the thermode was placed on the plantar rather than the dorsal surfaces of the feet (Fowler et al, 1987), thermal properties of the skin show marked variation between sites (Stevens et al, 1974). Winer et al (1992) also preceded their tests by establishing an approximate value for the threshold before ®ne tuning the measurements, a step which we have omitted.…”

Normal distributions of thermal and vibration sensory thresholds

“…1,5,6,11,13,17,18,22,32,33,44 Our results emphasize the necessity of including an adequate representation of older subjects, especially when investigating the discriminative properties of the test. The most striking effect of age was seen in vibration thresholds, which become increasingly variable for subjects over the age of 65 years.…”

“…42 A somewhat weaker but similar effect has been seen for thermal thresholds. 5,6,11,17,32,33 Analyses are frequently stratified by gender, but this effect on sensation thresholds may be confounded by height differences. 29 In studies where height was measured, it was associated with an increase in threshold values in the lower limbs.…”

Sex differences in age-related changes on peripheral warm and cold innocuous thermal sensitivity

“…That is, thermal sensitivity will decline in a similar manner between males and females with the ageing process. In contrast, Fowler et al [5346] reported greater increases in the warm threshold detection (i.e. sensitivity declined) in comparison to cold threshold detection in aged individuals; suggesting that the unmyelinated fibres were age affected.…”