White matter microstructure degenerates in patients with postherpetic neuralgia

The central mechanisms underlying postherpetic neuralgia (PHN) pain remains unknown. The primary purpose of this study was to identify microstructural white matter changes closely related to the PHN pain by means of diffusion tensor imaging (DTI) and tract-based spatial statistics (TBSS) analysis.

DTI data of the brains were obtained from 8 PHN patients and 8 healthy controls (HC) that were matched in age, gender, and educational level. DTI metrics, including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD), were separately compared between the two groups using TBSS analysis to detect subtle microstructural changes. Partial correlation analyses were also conducted to evaluate the association between the altered DTI measures and clinical features.

Average diffusion indices of white matter skeletons in the whole-brain showed no significant difference between the two groups. However, compared to the HC group, patients with PHN pain revealed reductions in localized FA and AD values in white matter underlying insula, occipital lobe, cerebellum, precentral gyrus, and many other regions, but without distinct change in regional MD and RD levels. In addition, decline of FA and AD values in patients represented significant negative correlations with PHN pain duration when the effect of VAS scores were excluded.

The current study suggest that there exists altered microstructure integrity of white matter in multiple brain regions in patients with PHN, and these changes increase in size as the duration of the pain increases. These findings might provide a new insight into the mechanism of PHN pain in brain.