Impaired Hemodynamic Response to Thermal Pain in Painful Diabetic Neuropathy

Abstract

Objective: Painful diabetic peripheral neuropathy (painful-DPN) causes distressing neuropathic pain that is only partially responsive to treatment. A better understanding of CNS correlates of painful-DPN is vital to develop more effective therapeutics. The aim of this study was to measure cerebral perfusion of the pain processing areas of the brain using MR-Dynamic Susceptibility Contrast (MR-DSC) imaging at rest and under experimental pain condition. Methods: 55 T1DM subjects (20 painful-DPN, 23 painless-DPN, 13 no-DPN) and 19 Healthy Volunteers (HV); underwent detailed clinical and neurophysiological assessment (NISLL+7 tests of nerve function; DN4 questionnaire). MR images were obtained at 3T using a MR-DSC, T2*-weighted technique (TR/TE=1250/35ms; 72 dynamics) to assess the passage of a bolus of intravenous gadolinium-chelate through cerebral vascular bed. Subjects were scanned at baseline and during 90s of heat-pain applied to the right lateral thigh (non-neuropathic area). The time-to-peak (TTP) concentration of gadolinium in regions of interest (ROI): right and left thalamus, right and left sensory cortices (RSC and LSC), was measured. Results: At baseline, although the mean TTP (s) in the ROIs was shorter in the painful-DPN group [e.g., RT: M (SD): 9.22 (1.13) vs. HV 9.83 (0.99), no-DPN 9.59 (0.90), painless-DPN 9.94 (0.97)] this was not statistically significant (p=0.058). However the ΔTTP in response to thermal pain was significantly different between the groups LT (p=0.021), RT (p=0.003), LSC (p=0.009), RSC (p=0.008). Whilst HV respond to thermal pain by shortening the TTP in ROI the painful-DPN group do the reverse (p<0.05). Conclusion: Subjects with painful-DPN have a paradoxical increase in TTP, indicating that chronic neuropathic pain state may result in a failure to mount a hemodynamic response to external pain and descending inhibition. This novel finding may serve as an objective marker of painful-DPN, and in the future may facilitate the development of novel treatments. Disclosure M. Greig: None. I.D. Wilkinson: None. D. Selvarajah: None. P. Shillo: None. R. Gandhi: None. S. Tesfaye: Speaker's Bureau; Self; Pfizer Inc.. Other Relationship; Self; Janssen Pharmaceuticals, Inc., Takeda Development Centre Europe Ltd.. Advisory Panel; Self; Wörwag Pharma GmbH & Co. KG.