Measurement of the pain threshold determined by electrical stimulation and its clinical application

INVESTIGATIONS of the sensory threshold to stimulation of the skin have become increasingly intensive during the last sixty years.lg2 Electrical stimuli were selected in this investigation to determine the pain threshold because of the following advantages of this method: 11 It is a simple way in which an exactly measurable and, therefore, reproducible stimulus can be applied over various regions of the body and can easily be expressed in physical terms (milliamperes). 21 It has the least chance of damaging the tissues. 31 It produces an easily recognizable and easily definable “pricking pain” sensation. The clinician needs to measure the pain sense quantitatively instead of relying on his subjective impression obtained with the help of his so-called “neurologic pin.” In this study, we define pain threshold in the same way as Bonica,3 that is, as the lowest electrical current-expressed in milliampereswhich at a fixed frequency and impulse duration first evokes a sensation of (pricking) pain. The purpose of this study was to develop a practical and reliable method for clinically determining pain thresholds of the skin, particularly in patients with disturbances of pain sensation. Specifically, this study attempted to establish those characteristics of a reproducible electrical stimulus necessary to measure and standardize the pain threshold of the skin. The following problems also were investigated: [l] the relationship and characteristics of an electrical stimulus required for its being exactly reproducible as pain threshold stimulus, [2] factors which might influence the pain threshold, [3] possible variations of the pain threshold in the course of time (in the same individual), [4] the pain threshold of different parts of the body surface, [5] possible variation of the pain threshold in different individuals, and [6] the influence of diseases of the nervous system on the pain threshold. The electrical method with square wave impulses has many advocates as noted by BjOrt~,~ Sige1,S Chemnitius and associates,6-H and Blake and associate^.^ Harris and Blockuslo described this method as being perhaps one of the most suitable for future use because it is very simply applied and constant reproducibility of the stimulus is possible. A survey of the literature regarding electrical stimulation of the skin indicates that control of voltage alone is quite unsatisfactory. In this study, it is stressed that in electrical skin stimulation, the applied voltage does not