Medial plantar nerve conduction studies in healthy controls and diabetics

Objective To collect a reference material of the medial plantar nerve action potential, to test intra/interobserver reliability in healthy controls and to apply the test to a group of patients with diabetes mellitus. Methods 98 healthy controls and 50 patients with diabetes mellitus were included. The medial plantar nerve was stimulated orthodromically and recorded with a surface electrode. In the patient group, NCS of motor and sensory nerves and quantitative sensory testing were also performed. Results Responses of the medial plantar nerve were obtained from all controls except from one aged 72. Amplitude decreased with age (r = −0.68, p < 0.0001). Intra/interobserver reliability was acceptable. 52% of the patients had abnormal overall NCS classification. Forty-eight percent had delayed tibial F-response latency. The medial plantar NCS were abnormal in 59% of the cases (47% abnormal NAP amplitude and 39% reduced CV), 59% of those with abnormal NCS had symptoms of sensory polyneuropathy. Only 24% had abnormal sural amplitude. Cold perception threshold was abnormal in more patients (30%) than warmth perception threshold (14%). Conclusions Responses were easily obtained in controls under 70 years. In diabetics the amplitudes of the medial plantar nerve were abnormal more often than in the sural nerve. Significance The medial plantar nerve response is reliable in patients under 70 years, and intra/interobserver reliability is acceptable.