A novel method of pain related potentials elicited by electrical stimulation of skin for early detection of diabetic small-fiber neuropathy

Objective: To investigate whether pain related evoked potentials (PREP) elicited by non-invasive trans-cutaneous electrical stimulation could be useful in detection of diabetic small fiber neuropathy.

Methods: We studied two groups of healthy controls ('young': N=36, 8 females, mean age=22 years, range [19–29], 'older': N=24, 14 females, mean age=46.5 years, range [30–65]) and two groups of patients with diabetes (‘with neuropathic symptoms': N=35, 15 females, mean age=52 years, range [36–64] and 'without symptoms': N=24, 8 females, range [32–64]). We included only diabetic patients without any abnormalities in routine nerve conduction studies. We investigated PREP over Cz vs. earlobes and measured latencies (ms) and NP peak-to-peak amplitudes (µV).

Results: Latencies and amplitudes did not differ between 'young' controls (right arm 148±13ms, 30±12µV; left arm 149±11ms, 29±10µV; right leg 177±12ms, 25±9µV; left leg 175±15ms, 24±7µV) and 'older' controls (right arm 149±7ms, 27±12µV; left arm 148±9ms, 30±11µV; right leg 184±16ms, 22±9µV; left leg 179±15ms, 21±8µV). In patients with neuropathic symptoms we found an increase in latencies and decrease in amplitudes from upper limbs (right arm 176±27ms, 20±12µV, left arm 176±30ms, 21±13µV) and lower limbs (right leg 224±25ms, 16±7µV; left leg 217±24ms, 15±9µV). In patients without symptoms we observed an increase of latencies and decrease of amplitudes from lower limbs (right leg 203±27ms, 18±7µV; left leg 198±28ms, 19±8µV), while PREP form arms were normal (right arm 156±19ms, 28±13µV, left arm 153±18ms, 26±10µV).

Conclusions: This novel technique was sensitive in detecting abnormalities of peripheral nerve function in the early phase of diabetes while the standard nerve conduction studies were normal. In summary, the method is cheap, non-invasive, easy to perform and could be widely used in addition to the routine electrophysiological methods for early detection of small fiber neuropathies.