Microstructural Abnormalities in Gray Matter of Patients with Postherpetic Neuralgia: A Diffusional Kurtosis Imaging Study.

BACKGROUND Changes in functional activity and connectivity have been shown in patients experiencing postherpetic neuralgia (PHN) pain. However, PHN-induced structural changes, particularly in the gray matter of which volume and density was widely reported to be altered by other chronic pain, have not been well characterized. OBJECTIVE In this study, we aimed to detect the difference in the microstructure of gray matter of PHN patients as compared to the healthy controls, and to analyze the correlation between microstructural alterations and clinical features of PHN patients. STUDY DESIGN Observational study. SETTING University hospital. METHODS Diffusional kurtosis imaging (DKI) was performed in 19 patients with PHN and in 19 age- and gender-matched healthy controls. Maps of axial kurtosis (K//), mean kurtosis (MK), radial kurtosis (K) in gray matter were calculated and compared between the 2 groups. Correlations between kurtosis metrics in the regions where between-group difference was detected and pain intensity as well as lesion duration were tested by Pearson's correlation. RESULTS Compared with healthy controls, PHN patients exhibited significantly decreased DKI parameters in the bilateral insula and superior temporal gyrus, left middle frontal gyrus and occipital lobe, right cerebellum anterior lobe, right thalamus, caudate and parahippocampal gyrus. K// in the bilateral insula and MK in the right insula were negatively correlated with visual analogue scale (VAS) scores of PHN patients, whereas no correlation was found between DKI parameters and lesion duration of PHN pain. LIMITATION Relatively small sample size. We still cannot determine the causal and effect relationship between the microstructural abnormalities in the gray matter and PHN. CONCLUSIONS DKI can specifically reflect pathophysiological microstructural alterations in the cerebral gray matters of PHN patients. This feature enables magnetic resonance imaging (MRI) to be a potentially valuable technique for objectively estimating the severity of PHN pain, which would provide an opportunity for elucidating the central mechanisms underlying PHN as well. KEY WORDS Postherpetic neuralgia, diffusional kurtosis imaging, insula cortex, gray matter, voxel-based analysis.