Clinical utility of somatosensory evoked potentials in diabetes mellitus

The posterior tibial nerve and median nerve somatosensory evoked potentials (PTN-SEPs and MN-SEPs) were investigated in 34 patients with diabetes mellitus (DM). We measured the latency of the first positive cortical potential (the cortical P37) of PTN-SEPs and that of the first negative cortical potential (the cortical N18) and Erb's potential of MN-SEPs. In 18 patients (52.9%), the cortical P37 latency was more than 3 SD longer than normal in the tibial nerve. There were positive correlations between the latency of cortical P37 and the duration of DM and the motor nerve conduction velocity of the posterior tibial nerve. Sensory action potentials of the posterior tibial nerve were not detectable in 21 patients, though cortical P37 potential was unambiguously recorded by stimulating the posterior tibial nerve even in those subjects. Diabetic retinopathy and nephropathy also tended to rise with increasing latency of cortical P37. The latency of cortical P37 is an important parameter in assessing diabetic neuropathy.