Peripheral, synaptic and central neuronal transmission is affected in type 1 diabetes

AIMS: We hypothesized that adults with type 1 diabetes and severe polyneuropathy have alterations in neuronal transmission at different anatomical levels. The aims were to investigate upstream sensory neuronal activation in terms of peripheral, spinal, precortical, and cortical transmission. METHODS: 48 participants with type-1 diabetes and polyneuropathy, and 21 age-matched healthy participants were included. Electrophysiological median nerve recordings were used to analyze peripheral transmission at Erb's point (P9-N11); spinal evoked potentials at Cv7 (P11-N14); subcortical evoked potentials at Oz (N14-P18); early cortical evoked potentials at CP5 (N20-P22); late cortical evoked potentials at C1 (N60-P80) and estimated cortical inter-peak latencies as measures of central conduction time. RESULTS: In comparison to healthy, the presence of diabetes prolonged peripheral transmission at P9 and N11 (+0.49 ms, p = .000; +0.47 ms, p = .04, respectively), early cortical evoked potentials at CP5: N20 (+2.41 ms, p = .003) and P22 (+5.88 ms, p = .001) and cortical potentials at C1: N60 (+39.08 ms, p = .001) and P80 (+54.55 ms, p = .000) and central conduction time. Decreased amplitudes were shown peripherally (-2.13 μV, p = .000), spinally (-0.57 μV, p = .005) and pre-cortically (-0.22 μV, p = .004). In both healthy and people with diabetes increased central conduction time were associated with decreased parasympathetic tone (ρ = -0.52, p = .027; ρ = -0.35, p = .047, respectively). CONCLUSION: Neuronal afferent transmission and brain responses were significantly impaired in diabetes and the presence of prolonged central conduction time is indicative of severe extensive neuronal damage. Trial registry number: EUDRA CT: 2013-004375-12; clinicaltrials.gov: NCT02138045.