Trial of a Trivial Quantitative Heat-Pain Stimulus for Detecting Severe Loss of Nociception

Background: Loss of nociception (LON) at the feet of persons with diabetes mellitus develops gradually over years and remains asymptomatic until the first painless diabetic foot ulceration (DFU). Severe LON with pain insensitivity can be diagnosed with a mechanical (pinprick) pain stimulus of 512-mN force. A comparable “suprathreshold” heat-pain stimulus may have the same potential. Objective: A six-second, 51°C heat-pain stimulus delivered on a 38.5-mm² spot by a commercial medical device (bite away®, to treat insect bites) was explored in a prospective cross-sectional diagnostic accuracy study to detect DFU-related LON. Methods: Seventy-two participants were studied: 12 with and 30 without diabetic neuropathy according to the conventional criteria, and 30 patients with a history of painless DFU (indicative of end-stage LON, reference standard). The feet were stimulated at the plantar and dorsal sides. A palmar surface was stimulated for control purposes. Participants scored stimulated pain intensity 0 to 10 on a numerical rating scale. Results: At hands, pain intensity was rated six on average by all participants. Persons without neuropathy scored 7 (0-10), median (range), at the plantar side and 8.5 (2-10) at the dorsal side of the foot, while those with DFU scored 0 (0-8) and 0 (0-10), respectively. A pain response of 0 at the foot dorsum detected DFU-related LON with a sensitivity of 65% (specificity, 100%; positive and negative predictive values, 100% and 96%, respectively). Conclusions: Due to its high specificity, the test seems advantageous for diagnostic purposes, complementary to current screening tests.