Thalamic neuronal dysfunction and chronic sensorimotor distal symmetrical polyneuropathy in patients with type 1 diabetes mellitus

Aims/hypothesis Although clear peripheral nerve pathological abnormalities have been demonstrated in diabetic peripheral neuropathy (DPN), there is little information with regard to brain involvement. Our aim was to use in vivo proton magnetic resonance specroscopy (H-MRS) in patients with DPN in order to assess the neuro-chemical status of the thalamus, which acts as the gateway to the brain for somatosensory information. Methods Participants included 18 type 1 diabetic men (eight without DPN, ten with DPN) and six non-diabetic healthy volunteers, who all underwent detailed clinical and neurophysiological assessments yielding a Neuropathy Composite Score (NCS) derived from Neuropathy Impairment Score of the Lower Limbs plus seven tests of nerve function prior to investigation via a single-voxel H-MRS technique, which was used to sample ventral posterior thalamic parenchyma. Spectroscopic resonances including those due to N-acetyl aspartate (NAA) were assessed at both short and long echo-time, providing putative indicators of neuronal function and integrity, respectively. Results At long echo-time we observed significantly lower NAA:creatine (p=0.04) and NAA:choline (p=0.02) ratios in DPN patients than in the other groups. No group differences were detected at short echo-time. We found a significant positive association between both sural amplitude (rho=0.61, p=0.004) and nerve conduction velocity (r=0.58, p=0.006) and NAA:creatine signal among participants with diabetes. Vibration detection threshold (rho=-0.70, p=0.004) was significantly related to NAA:choline ratio. Heart rate variability with deep breathing (rho=-0.46, p=0.05) and NCS (rho=-0.53, p=0.03) were significantly related to NAA:creatine ratio. Conclusions/interpretation The significantly lower NAA:creatine ratio in DPN is suggestive of thalamic neuronal dysfunction, while the lack of difference in short echo-time between the groups does not suggest neuronal loss. Taken together with the observed correlations between NAA and neurophysiological assessments, these findings provide evidence for thalamic neuronal involvement in DPN.