[Relationship between thermal threshold and population of peripheral nerve fibers]

The relationship skin thermal threshold (TT) and density of both myelinated and unmyelinated fibers were investigated in 12 patients with various peripheral nerve diseases including Crow-Fukase syndrome, carcinomatous neuropathy and Charcot-Marie-Tooth disease. The TT was measured at a site above the medial tibial condyle using a thermal threshold tester. The TT was defined as the threshold at which a slight rise or fall in temperature could be detected. The size of the skin stimulation area was 13.5 cm2, the temperature change rate was 1 degrees C/sec, and the basal temperature was set at 34 degrees C. A sural nerve biopsy was performed and an image processor (IBAS) was used to measure the nerve fiber density. The TT in the patients with peripheral nerve disease was found to be elevated when compared with that of the 74 healthy controls (mean age of 38.1 +/- 13.3 years). Elevation of the TT has an intimate relation to damage of the small myelinated nerve fibers. In conclusion, unmyelinated fibers may play a relatively minor role in conveying thermal sensation.