Structural and Functional Brain Abnormalities in Trigeminal Neuralgia: A Systematic Review

Aims: To evaluate the available literature on structural and functional brain abnormalities in trigeminal neuralgia (TN) using several brain magnetic resonance imaging (MRI) techniques to further understand the central mechanisms of TN. Methods: PubMed and Web of Science databases and the reference lists of identified studies were searched to identify potentially eligible studies through January 2019. Eligible articles were assessed for risk of bias and reviewed by two independent researchers. Results: A total of 17 articles meeting the inclusion criteria were included in this study. The methodologic quality of the included studies was moderate. A total of 10 studies evaluated structural gray matter (GM) changes, and there was reasonable evidence that the GM of some specific brain regions changed in TN patients. In addition, there was a significant change in the root entry zone of the trigeminal nerve and in several regions of white matter. Functional changes in resting state were assessed in 9 studies. TN patients showed increased activation of resting state, and this activation was reduced in specific brain regions. There were several studies that focused on the correlation between functional parameters or strength of functional connectivity and clinical features (eg, visual analog score and pain duration), but each study focused on different brain areas or different functional connectivities within the brain. Conclusion: There is moderate evidence that TN patients show structural brain differences in specific cortical and subcortical regions. In addition, TN patients show changes in pain-related functional connections in the resting state. Future research should focus on longitudinal designs and integration of different brain-imaging techniques. Keywords: functional connectivity, gray matter, trigeminal neuralgia, white matter