[Sensory nerve action potentials in the evaluation of diabetic polyneuropathy]

In order to clarify the suitability of sensory nerve action potential(SNAP) in the evaluation of diabetic polyneuropathy, we studied measurements of SNAPs in the median, ulnar and sural nerves. Subjects were 253 patients with non-insulin dependent diabetes mellitus; 167 men and 86 women, aged 58.2 +/- 12.8(mean +/- SD) years old. Their diabetic history was 10.2 +/- 8.6 years. SNAPs were recorded antidromically from index finger, little finger and lateral to the Achilles tendon, respectively. Twenty-eight patients, in whom any one of the SNAPs couldn't be obtained, were already excluded from this study. The polyneuropathy index (PNI) was calculated from 12 indices concerning to the velocity or long distance latency in motor nerve conduction studies of 4 nerves. The PNI is known to be an excellent index to express the degree of diabetic polyneuropathy. Amplitude and conduction velocity in each nerve was 28.6 +/- 15.6 microV and 46.2 +/- 7.4 m/sec in the median nerve, 26.7 +/- 15.8 microV and 47.0 +/- 6.5 m/sec in the ulnar nerve, 13.1 +/- 6.5 microV and 43.1 +/- 6.0 m/sec in the sural nerve, respectively. The coefficient of correlation of the measurements between median and ulnar nerves was larger than other assortment of nerves. The coefficient of correlation of each measurement with PNI was around 0.40 in the amplitude and around 0.55 in the conduction velocity. Nevertheless, the mean value of the 3 nerves had a higher coefficient of correlation with PNI; 0.48 in the amplitude and 0.60 in the conduction velocity. SNAP measurements of a single nerve are often largely affected by the inter-individual differences, inter-nerve differences or measuring errors. But the mean value of the 3 nerves will be better in exploring the degree of diabetic polyneuropathy. Evaluation of diabetic polyneuropathy by SNAPs will be best achieved by using the mean value of these 3 nerves.