Thermal Threshold Testing For The Assessment Of Small Fiber Dysfunction - Normal Values And Reproducibility

Small and large fibre neuropathy are common findings in patients with long-standing diabetes mellitus. The Thermal Threshold Tester was tested to obtain normal values for thermal perception threshold for warmth and cold. This device produces thermal stimuli by means of a Peltier element placed on the skin. Warm and cold thresholds are measured using a forced choice method with an up-and-down-transform rule and expressed in degrees Celsius (degrees-C). Thresholds were measured at the right wrist and right foot in 80 normal subjects, divided into four age groups; 25-34, 35-44, 45-54, and 55-65 years. The repeatability coefficient was assessed by twice measuring 39 diabetic patients without known neuropathy. Warm thermal threshold in the hand showed a significant increase with age from 0.09 +/- 0.5 (mean +/- SD) in the youngest age group to 0.17 +/- 0.08-degrees-C (p < 0.05) in the oldest age group. Cold thermal threshold in the hand (varying between 0.08 +/- 0.04 and 0.14 +/- 0.05-degrees-C) and warm thermal threshold in the foot (varying between 2.45 +/- 1.93 and 4.06 +/- 2.57-degrees-C) did not differ significantly between the four age groups. There was a significant increase in cold thermal threshold in the foot with age, increasing from 0.31 +/- 0.24 to 0.56 +/- 0.44-degrees-C (p < 0.05). Reproducibility in the diabetic subjects was good for measurements of warm and cold threshold in the hand, but poor for warm threshold in the foot in the normal range and for cold thermal threshold in the abnormal range.