Capsaicin-Induced Changes in Electrical Pain Perception Threshold Can Be Used to Assess the Magnitude of Secondary Hyperalgesia in Humans

Abstract

Objectives Areas of secondary hyperalgesia can be assessed using quantitative sensory testing (QST). Delivering noxious electrocutaneous stimulation could provide added benefit by allowing multiple measurements of the magnitude of hyperalgesia. We aimed to characterize the use of electrical pain perception (EPP) thresholds alongside QST as a means by which to measure changes in pain thresholds within an area of secondary mechanical hyperalgesia. Methods EPP and heat pain thresholds (HPTs) were measured at five distinct points at baseline and following 1% capsaicin cream application, one within a central zone and four within a secondary zone. Areas of secondary mechanical hyperalgesia were mapped using QST. In a further 14 participants, capsaicin-induced reduction in EPP thresholds was mapped using a radial lines approach across 24 points. Results There was a reduction in EPP threshold measured at the four points within the secondary zone, which was within the mapped area of mechanical secondary hyperalgesia. The magnitude of secondary hyperalgesia could be split into a mild (∼4% reduction) and severe (∼21% reduction) area within an individual subject. There was no reduction in HPT within the secondary zone, but there was a reduction in both HPT and EPP threshold within the primary zone. EPP mapping revealed differences in the magnitude and spread of hyperalgesia across all subjects. Conclusions Measuring capsaicin-induced reduction in EPP thresholds can be used to map hyperalgesic areas in humans. This semi-automated approach allows rapid assessment of the magnitude of hyperalgesia, both within an individual subject and across a study population.

Priming of central and peripheral mechanisms with heat and cutaneous capsaicin facilitates secondary hyperalgesia to high-frequency electrical stimulation

“…A recent study observed a drop in electrical pain threshold in primary and secondary area of capsaicin injection (Hughes et al 2020) supporting the increased pain to HFS observed in the secondary area in the current study.…”

“…There are some controversies in the literature regarding heat hyperalgesia to capsaicin. Primary hyperlagesia to heat is well established (Hughes et al 2020;Lamotte et al 1991) as also observed with decreased HPT in the current study. A 1-2 cm zone of hyperalgesia to heat has been observed in few studies, which may still be within the primary hyperalgesic area (Lamotte et al 1991;).…”

“…One study however observed desensitization to heat stimuli in the area of injection (Ali et al 1996), but the area of stimulation with heat may affect the response, since a small laser was used in the study by (Ali et al 1996) compared to the 3x3 contact heat thermode applied in the current study. Secondary heat hyperalgesia has to the author knowledge not been observed (Ali et al 1996;Hughes et al 2020).…”

A novel implantable device for sensory and affective assessment of orofacial pain in rats

“…Despite pain research, electrical stimuli have also been widely used in testing of fear conditioning, learned helplessness, and aversion protocol ( 31 – 33 ). To quantitively measure the electoral thresholds, electrical stimuli is given at given intervals, with a fixed increment in intensity for both animal and human being ( 34 , 35 ). In current study, we applied square-wave electrical stimulation with a one-second duration, which is more relevant to clinical manifestation that directly excites full spectrum of peripheral nociceptors in trigeminal neuralgia cases.…”

Modified Sensory Testing in Non-verbal Patients Receiving Novel Intrathecal Therapies for Neurological Disorders

“…Typically, a calibrated stimulus is applied to the skin in graded intensities, and the patient's perception is recorded. Stimulus modalities can be mechanical (i.e., monofilaments, pin-prick, vibratory), thermal (i.e., Peltier thermode), or electrical ( 17 , 18 ). Outcome measures include stimulus detection (present/absent) and stimulus intensity (self-reported rating).…”