Cerebrospinal Fluid in Classical Trigeminal Neuralgia: An Exploratory Study on Candidate Biomarkers

Pathophysiology and Management of Refractory Trigeminal Neuralgia

PURPOSE OF REVIEW

Discuss the current understanding of the pathophysiology and management of refractory trigeminal neuralgia (TN). This includes a discussion on why TN can recur after microvascular decompression and a discussion on "outside of the box" options when both first- and second-line management strategies have been exhausted.

RECENT FINDINGS

This review discusses second- and third-line oral medication options, botulinum toxin A, repeat microvascular decompression, repeat ablative procedures, internal neurolysis, trigeminal branch blockade, and neuromodulation using TMS or peripheral stimulation. Additional management for chronic neuropathic facial pain such as deep brain stimulation, motor cortex stimulation, and focused ultrasound thalamotomy are also discussed, though evidence in trigeminal neuralgia is limited. Treatment of recurrent TN despite multiple surgeries can be challenging, and multiple minimally invasive and more invasive management options have been reported in small studies and case reports. Further studies are needed to determine an optimal stepwise approach.

Genomic Validation in the UK Biobank Cohort Suggests a Role of C8B and MFG-E8 in the Pathogenesis of Trigeminal Neuralgia

Trigeminal neuralgia (TN) is a severe facial pain disease of uncertain pathophysiology and unclear genetic background. Although recent research has reported a more important role of genetic factors in TN pathogenesis, few candidate genes have been proposed to date. The present study aimed to identify independent genetic variants in the protein-coding genes associated with TN. We focused on genes previously linked to TN based on the results of four proteomic studies conducted by our research team. The goal was to validate these findings on the genetic level to enhance our understanding of the role of genetics in TN. The study is based on the participants from UK Biobank cohort. Following quality control, 175 independent single nucleotide polymorphisms (SNPs) in 17 genes were selected. The study sample comprised of diagnosed TN cases (N = 555) and randomly matched controls (N = 6245) based on specific criteria. Two SNPs corresponding to C8B rs706484 [odds ratio (OR) (95% confidence interval (CI)): 1.357 (1.158-1.590); p: 0.00016] and MFG-E8 rs2015495 [OR (95% CI): 1.313 (1.134-1.521); p: 0.00028] showed significant positive association with TN, indicating a positive effect of the SNP alleles on gene expression and disease risk. Interestingly, both SNPs are Expression Quantitative Trait Loci (eQTLs), and are associated with changes in the expression activity of their corresponding gene. Our findings suggest novel genetic associations between C8B, a key component of the complement system, and MFG-E8, which plays a role in regulating neuroinflammation, in relation to TN. The identified genetic variations may help explain why some individuals develop TN while others do not, indicating a potential genetic predisposition to the condition.

Trigeminal neuralgia

Trigeminal neuralgia (TN) is a facial pain disorder characterized by intense and paroxysmal pain that profoundly affects quality of life and presents complex challenges in diagnosis and treatment. TN can be categorized as classical, secondary and idiopathic. Epidemiological studies show variable incidence rates and an increased prevalence in women and in the elderly, with familial cases suggesting genetic factors. The pathophysiology of TN is multifactorial and involves genetic predisposition, anatomical changes, and neurophysiological factors, leading to hyperexcitable neuronal states, central sensitization and widespread neural plasticity changes. Neurovascular compression of the trigeminal root, which undergoes major morphological changes, and focal demyelination of primary trigeminal afferents are key aetiological factors in TN. Structural and functional brain imaging studies in patients with TN demonstrated abnormalities in brain regions responsible for pain modulation and emotional processing of pain. Treatment of TN involves a multifaceted approach that considers patient-specific factors, including the type of TN, with initial pharmacotherapy followed by surgical options if necessary. First-line pharmacological treatments include carbamazepine and oxcarbazepine. Surgical interventions, including microvascular decompression and percutaneous neuroablative procedures, can be considered at an early stage if pharmacotherapy is not sufficient for pain control or has intolerable adverse effects or contraindications.

Heightened presence of inflammatory mediators in the cerebrospinal fluid of patients with trigeminal neuralgia

Introduction

Trigeminal neuralgia (TN) is a chronic, debilitating facial pain disease causing stabbing pain attacks in the sensory distribution of the trigeminal nerve. The underlying pathophysiology of TN is incompletely understood, although microstructural abnormalities consistent with focal demyelination of the trigeminal nerve root have been shown in patients with TN. Studies of the cerebrospinal fluid (CSF) in patients with TN suggest an increased prevalence of inflammatory mediators, potentially implicating neuroinflammation in the pathophysiology of TN, as it has been implicated in other chronic pain conditions.

Objectives

This study aimed to further assess the inflammatory profile of CSF in TN.

Methods

Cerebrospinal fluid was collected from 8 medically refractory patients with TN undergoing microvascular decompression surgery and 4 pain-free controls (2 with hemifacial spasm; 2 with normal pressure hydrocephalus). Cerebrospinal fluid was collected from the cerebellopontine angle cistern intraoperatively in the patients with TN. Inflammatory profiles of CSF samples were analyzed using a 71-plex cytokine and chemokine multiplex assay.

Results

Ten inflammatory markers were found to be significantly higher in TN CSF, and no analytes were significantly lower. Elevated factors can be classified into pro-inflammatory cytokines (IL-9, IL-18, and IL-33), chemokines (RANTES and ENA-78), the tumor necrosis factor superfamily (TRAIL and sCD40L), and growth factors (EGF, PDGF-AB/BB, and FGF-2).

Conclusion

This study further supports the notion that neuroinflammation is present in TN, and that multiple molecular pathways are implicated.

CSF neuron-specific enolase as a biomarker of neurovascular conflict severity in drug-resistant trigeminal neuralgia: a prospective study in patients submitted to microvascular decompression

BACKGROUND

Although neurovascular conflict (NVC) is the most widely accepted cause of trigeminal neuralgia (TN), few articles have analyzed molecular and biochemical mechanisms underlying TN. In the present study, we dosed neuron-specific enolase (NSE) on serum and CSF samples of 20 patients submitted to microvascular decompression (MVD) and correlated these findings with the type of NVC.

METHODS

Blood samples were obtained preoperatively and 48 h after MVD. CSF from trigeminal cistern was intraoperatively obtained. NSE levels were measured using the Diasorin kit (LIAISON®NSE). NVC was classified as "contact" or "trigeminal nerve distortion/indentation" or "trigeminal root atrophy" based on MRI and intraoperative findings. Clinical outcome was measured by acute pain relief (APR) and Barrow Neurological Institute (BNI) scale at last available follow-up (FU; 6.40 ± 5.38 months).

RESULTS

APR was obtained in all patients. A statistically significant BNI reduction was obtained at latest FU (p < 0.0001). Serum NSE levels significantly decreased following MVD (from 12.15 ± 3.02 ng/mL to 8.95 ± 2.83 ng/mL, p = 0.001). The mean CSF NSE value was 48.94 ng/mL, and the mean CSF/serum NSE rate was 4.18 with a strong correlation between these two variables (p = 0.0008). CSF NSE level in "trigeminal root atrophy" group was significantly higher compared to "contact" (p = 0.0045) and "distortion/indentation" (p = 0.010) groups.

CONCLUSION

NSE levels seem to be related to the etiopathology and severity of NVC. A significant reduction of serum NSE levels could be related to the resolution of the NVC and clinical TN improvement.