Objective
The purposes of this study were to obtain the reference values of latency and amplitude of the medial plantar sensory nerve action potential(SNAP) in normal controls and to evaluate the diagnostic sensitivity of medial plantar sensory nerve conduction study(NCS) in diabetic neuropathy.

Method
Thirty healthy controls(mean age, 48.7 years; range, 38∼59 years) and 33 diabetic patients(mean age, 50.8 years; range, 37∼64 years) were included in this study. The inclusion criteria for diabetic patients were subjects with the normal peroneal and tibial compound muscle action potentials, obtainable sural SNAPs and intact pressure-perception to Semmes-Weinstein monofilament^Ⱂ 5.07.

Results
The medial plantar sensory nerve action potentials were obtainable in all control subjects and the reference values of onset latency and peak to peak amplitude were 4.29⁑0.49 msec and 3.1⁑1.34 ㄍV, respectively.

All 33 diabetic patients showed the normal latency and 3 of them showed the low amplitude in sural SNAPs. The medial plantar SNAPs were obtainable in 24 diabetic patients. Among 9 patients with unobtainable medial plantar SNAPs, 6 showed the normal sural SNAPs and 3 showed the low sural SNAPs. The sensitivities of medial plantar SNAPs to sural nerve and sural SNAPs to medial plantar sensory nerve were 100%(3/3) and 27.3%(3/11) respectively.

Conclusion
We concluded that medial plantar sensory NCS was more valuable in the early diagnosis of diabetic neuropathy than the sural NCS and Semmes-Weinstein monofilament^Ⱂ(North Coast Medical Inc, USA).