SYNOPSIS A quantitative method for the examination ofthermal sensibility was applied in 26 normal subjects and in patients with various neurological disorders. The stimulation technique resembled Bekesy audiometry: the patient reversed the direction of the temperature change of a thermode whenever warm, cold, or thermal pain thresholds were reached. The resulting temperature curve enables a quantitative description of the subject's thermal sensibility and of the degree of impairment displayed by neurological patients.It is well known that a disturbance of the temperature sense occurs in many neurological patients as a consequence of lesions in the peripheral or central nervous system. It usually occurs together with a disturbance of other sensory modalities such as cutaneous pain, but it may also appear separately (Goldscheider, 1926).For a closer study of changes in thermal sensibility, a quantitative technique is necessary which allows reliable measurement of warm, cold, and thermal pain thresholds by pure thermal stimuli without tactile components. The method should be easy and quick enough to be combined with routine neurological examination. Although in neurophysiological and psychophysical research several methods have been developed for the study of temperature sensibility (for references cf Kenshalo, 1970), all of them are too complicated and time consuming to be applied FIG. 1 The Marstock stimulator. A thermocouple is clinically. The technique described here has proved to fixed to the centre of the stimulating surface (area be easy enough to be used routinely and repeatedly in 25 x 50 mm). patients in whom it was desirable to establish the degree or the temporal course of a neurological disorder affecting thermosensibility.tions which produce a temperature difference between METHODS upper and lower side of the stimulator when a current STIMULATOR is passed through them. As the reverse side of the stimulator is thermally buffered by a metal block perThe thermostimulator has a rectangular stimulating fused with water of 30°C temperature, the stimulating surface of 25 x 50 mm (Fig. 1), and it operates on the surface can be either warmed or cooled depending on Peltier principle. It consists of semiconductor junc-the direction of the current. The temperature is

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Changes in perception of pure thermal stimuli delivered to the hand at threshold intensity were observed during ischemic nerve block in 27 healthy subjects in order to study the significance of unmyelinated cutaneous cold receptors for thermal sensibility. Paresthesias and an increasing feeling of numbness were followed by a sudden change in cold sensation which developed a clearly dysesthetic quality. When complete motor block was reached and no myelinated axon functions were left, cold stimuli were still clearly but abnormally perceived. Warm sensation was little affected during the whole course of nerve block. The results indicate that the information from unmyelinated low threshold cold receptors alone leads to a dysesthetic cold sensation which normally is suppressed by the activity of myelinated cold afferents. Obviously these receptors are not needed for the discrimination of minor cold stimuli but they seem to be essential for the perception of the first burning cold pain.

In order to substantiate accidental observations on the influence of skin temperature on itch, and to elucidate a possible involvement of thermoreceptors in itch generation, the effects of thermostimulation on clinical and experimental itch were studied. Eighteen patients with atopic dermatitis rated the intensity of spontaneous itch on one of their forearms before, during, and after its immersion in a waterbath of either 10 degrees C or 45 degrees C. In 40 normal subjects itch was elicited by histamine topically applied to a 7 cm2 skin area of the volar forearm. Before and after histamine application thermal thresholds were recorded. Then the skin area was heated or cooled at a rate of 0.5 degrees C/sec and itch intensity was continuously rated. Cooling abolished itch in all patients and in most of the normal subjects. Heating produced less clear effects: in two-thirds of both patients and normal subjects itch disappeared or was reduced whereas in the others itch was aggravated. Usually after the end of thermostimulation the opposite changes in itch intensity occurred. In the normal subjects thermal thresholds were not significantly influenced by histamine. Over a certain temperature range itch and thermal sensations could coexist as separate modalities. The results indicate that changes in skin temperature have a marked influence on itch intensity. Whereas cooling seems to act directly on the sensory receptors mediating itch, warm stimuli could have a central inhibitory effect. A direct role of thermoreceptors in the generation of itch is improbable.