Tracking the microstructural changes of Trigeminal Ganglion in Chronic Ocular Surface Pain Patients: A Diffusion MRI Study

Abstract

Purpose : Chronic ocular pain (OP) persists for 3+ months and can occur without detectable ocular surface pathology. Noxious stimuli are transduced by corneal afferent nociceptors, which are extensions of the sensory axons of trigeminal ganglion (TG) neurons. Our objective was to demonstrate the feasibility of using diffusion tractography to differentiate individuals with and without chronic OP based on TG microstructure.

Methods : The study included 40 cases (26M:14F, 56±11 y.o.) with chronic OP and 17 controls without OP (12M:5F, 55±9 y.o) seen at the Miami Veterans Affair Eye Clinic. Patients were classified as having OP if they had eye pain ≥3 months and an average ocular pain rating over 1 week recall ≥1 (Numeric Rating Scale 0-10). MRI was performed using a 3T Siemens MAGNETOM Vida scanner (Erlangen, Germany). Tractography pathways were reconstructed using DSI-Studio with generalized Q-sampling imaging method. Regions of interests were manually placed to detect TGs. Diffusion metrics such as fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), and normalized quantitative anisotropy (NQA) were recorded.

Results : The OP cohort (n=31) reported NRS pain scores of 4.5±2.8 out of 10 (Range:1-10), while controls (n=14) reported no pain. TGs in 45 subjects were successfully reconstructed (Fig.1). 12 subjects (9 OP, 3 controls) were excluded due to the inability to visualize TG (n=11) and algorithm inability to complete tractography reconstruction (n=1). Diffusion metrics for the right TG were similar between OP and controls. However, OP cohort had significantly decreased MD (p= 0.010), AD (p=0.015), RD (p= 0.008), and NQA (p=0.017) vs. controls (Fig.2). Decreased NQA and AD are mostly interpreted as reduced diffusion bias in tissue suggestive of axonal loss, while decreased MD is suggestive of restricted diffusion due to dense cellular/axonal packing or cytotoxic edema. Reduced RD could be interpreted as a microstructural disruption of white matter.

Conclusions : Microstructural alterations were detected in the left TG of subjects with chronic OP vs. controls without OP. More studies are needed to understand the clinical implications of these findings.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Figure 1: TG tractography (green), T1 underlay with axial and sagittal views. Control (F, 61 y.o) A: anterior, P: posterior. x,y,z showing image orientation

 

Figure 2: Box plot of left TG