Noxious heat hyperalgesia test instrument.

ABSTRACT

A simple feedback thermode has been developed to quantify cutaneous hyperalgesia to noxious heat. A noxious temperature set between 42 degrees C and 60 degrees C is applied to a test site by the subject. A resettable impedance timing circuit measures the contact duration to +/- 0.01s. Despite site-to-site, inter- and intra-subject variability, the test sensitivity is enhanced by comparing affected and corresponding normal skin in the same subject. This test strategy was used in 55 subjects in whom topical 0.025 to 0.05% capsaicin application provoked hyperalgesia on the forearm and foot. Capsaicin-treated sites showed a significant reduction of 52 degrees C withdrawal latency (0.51-0.77 x normal mean; P less than 0.05). The device has been tested clinically in patients with diabetic neuropathy who had hypersensitivity to pinprick on one foot. A significant 42% difference was found between corresponding contralateral sites (P less than 0.05). These data suggest that even mild hyperalgesia is detectable using this instrument. It provides an objective measure of hyperalgesia which can be used to assess changes in nociceptive acuity.