2023 MSC Poster Contest Presentation: The impact of trigeminal neuralgia pain on the hippocampus and its major efferent pathway

The 2023 MSC Emerging Science Contest for Early-Career Investigators took place on December 13, 2023. Below is a written summary of one of the presentations from the contest. Read about other presentations from the event in our Early-Career Science Library.

Category: Trigeminal pain and headache

Runner up: Patcharaporn Srisaikaew, postdoctoral researcher at Krembil Brain Institute, Toronto Western Hospital, University Health Network, Canada

Title: The impact of trigeminal neuralgia pain on the hippocampus and its major efferent pathway.

Hypothesis, methodology, findings and conclusions.

Trigeminal neuralgia (TN) is an extremely severe type of neuropathic pain affecting the face. In our research, we explored the impact of TN on the brain’s memory- and pain-related structures, specifically the hippocampus and its main efferent pathway, the fornix. We used advanced brain imaging approaches to examine these brain structures before and after surgery in 54 TN patients and compared them with 54 age- and sex-matched healthy individuals (HC).

Our findings showed that in TN patients, the hippocampus is significantly smaller in volume, and the fornix integrity is significantly reduced when compared to HC. After successful Gamma Knife Radiosurgery (GKRS) surgery, some of the hippocampal subfield volumes normalized but the fornix integrity remained abnormal, especially on the right hemisphere. This normalization was more prominent in patients who reported at least 75% pain relief after surgery, suggesting a link between brain structural alterations and pain modulation mechanisms and pain relief. Importantly, we demonstrated the reduction in hippocampus volume in TN is affected by TN pain and the effective surgery intervention could reverse this alteration. We further investigate the effect of sex and TN pain. Male TN patients six months after surgery demonstrate a further fornix integrity reduction compared with females, suggesting that males’ and females’ TN may be responding to the treatment differently. Our research highlights the significant impact of chronic pain on both the overall structure (hippocampus volume) and the connections (fornix integrity) in the human brain’s memory circuitry. These insights could lead to improved biopsychological treatments and outcomes for chronic pain patients.

Implications for understanding migraine disease and/or its comorbidities, or how the research holds promise as a new avenue of future migraine study.

TN and migraine disease share some overlapping aspects, particularly in their impact on neurological features and individual daily activities and a higher prevalence in females than in males. Several studies reported a mechanistic link between migraine and patients with TN. For instance, migraine episodes often result from an activation of the trigeminal nerve and treating the irritation of the trigeminal nerve can also calm the migraine episode. Moreover, migraine is not only frequently reported in patients with TN, but also found to be one of the risks of disease progression. This pinpointed the crucial query of the past history of migraine in the study of TN. Given that TN is highly amenable to surgery, along with the prolonged pain relief after surgical treatment in ~75% of patients, TN is an excellent model to study the impact of pain processing and pain modulation on brain structure and function in chronic pain populations. The identification of changes in the hippocampus and fornix in TN patients contributes valuable insights into the structural alterations associated with chronic pain conditions, including migraine disease. The observed changes in hippocampus volume and its connection, the fornix integrity, shed light on the impact of chronic pain on the brain’s structure. Understanding both the commonalities and differences between TN and migraine is essential for accurate diagnosis and effective management. In particular, this study will deepen our understanding of the relationship between chronic pain and the dynamic changes in brain structure, and will lead to improved diagnosis, treatment, and outcomes in chronic pain disorders including migraine disease.