Trigeminal nerve microstructure in chronic temporomandibular joint pain: A diffusion tensor imaging study

Objective To evaluate whether chronic temporomandibular joint (TMJ) pain secondary to internal joint disorders is associated with microstructural alterations of the trigeminal nerve (TN), assessed by diffusion tensor imaging (DTI) and fractional anisotropy (FA). Methods Forty individuals were included: 20 patients with chronic TMJ pain and 20 pain-free controls. All participants underwent magnetic resonance imaging with DTI focused on the cisternal segment of the TN. FA values were measured bilaterally. Between-group comparisons were performed using Mann-Whitney tests, and associations between FA and clinical variables were assessed using Spearman rank correlations. Results No significant side-to-side FA difference was observed in controls (P = 0.20), and no significant FA difference was detected between painful TMJs and control sides (P = 0.75). FA was not associated with pain duration (P = 0.50) or pain intensity during mandibular function (P = 0.64). In contrast, among TMJs with pain at rest, greater resting pain intensity was significantly associated with lower ipsilateral TN FA (21 TMJs from 15 patients; Spearman ρ = −0.51, P = 0.019). Conclusion Chronic TMJ pain secondary to internal joint disorders was not associated with a detectable global reduction in cisternal TN FA. However, the inverse association between resting pain intensity and ipsilateral FA suggests subtle pain-related microstructural variation in a clinically relevant subgroup. These findings support further investigation of trigeminal neuroplasticity in persistent TMJ pain while avoiding interpretation of FA as a direct marker of structural nerve damage.