Gray matter volume reduction reflects chronic pain in trigeminal neuralgia

Aims: Trigeminal neuralgia (TN) is caused by an ecstatic blood vessel affecting the trigeminal nerve at the root entry zone of the brain stem. Recent evidence suggests an additional central component within the trigeminal pain-processing network in the pathophysiology of TN. Objective: To detect gray matter changes in patients with TN compared to healthy controls and to identify specific brain areas that may be associated with the development and persistence of this debilitating facial pain condition. Methods: Sixty patients with classical TN were compared to 49 healthy controls using magnetic resonance imaging (MRI) based voxel-based morphometry (VBM). Eighteen patients had TN with concomitant constant facial pain, a condition previously described as predictor of worse treatment outcome. Results: We found gray matter volume reduction in TN patients compared to controls in areas of the brain generally associated with pain processing, such as the primary and secondary somatosensory cortex, thalamus, insula, anterior cingulate cortex (ACC), cerebellum, and dorsolateral prefrontal cortex. Gray matter volume within the ACC, hippocampus, and temporal lobe inversely correlated with increasing disease duration in TN. Conclusion: TN leads to gray matter volume reduction within the trigeminal pain-processing network. Whether one of these regions represents a central TN generator remains undetermined. The observed changes probably reflect the impact of multiple, daily attacks of trigeminal pain in these patients similar to what was previously described in other chronic pain conditions as a possible adaptation mechanism to chronic pain in regard to neuronal plasticity. ACC, hippocampus and temporal lobe volume reduction in parallel with disease duration may point to a pivotal role of these structures in the course of chronic pain.