Thermal Perception as a Key Factor for Assessing Effects of Trigeminal Nerve Injury.

AIMS: To conduct a functional examination using multimodal exploration of a sample of patients with iatrogenic trigeminal nerve injury to understand the underlying mechanisms of neuropathic pain following trigeminal nerve injury.

METHODS: Subjective and objective symptoms and responses to thermal and electrical quantitative sensory testing (QST) were evaluated in 85 patients with unilateral trigeminal nerve injury. Objective symptoms were measured by seven clinical sensory tests. Thermal QST included cold detection threshold (CDT), warm detection threshold (WDT), and heat pain threshold (HPT). Electrical current perception threshold was performed with electrical stimuli of 2,000, 250, and 5 Hz. The time since injury was included as a possible independent variable. The data were analyzed using chi-square test, independent t test, Mann Whitney U test, one-way analysis of variance (ANOVA), and Kruskal-Wallis test. Further analyses with Pearson correlation analysis, Spearman rank correlation analysis, and cluster analysis were applied.

RESULTS: Unlike objective symptoms, thermal and electrical QST values and subjective symptoms did not improve in patients with an old injury. Thermal QST, particularly WDT, showed the highest positive correlation with subjective symptoms in all tests. Cluster analysis of the thermal QST values identified three subgroups: cluster 1, which was characterized by prominent cold and warm hypoesthesia; cluster 2, which presented elevated WDT; and cluster 3, which showed the smallest thermal differences for all thermal variables but had the highest proportion of neuropathic pain.

CONCLUSION: These findings have demonstrated that thermal QST is a suitable tool for evaluating and characterizing the sensory effects of trigeminal nerve injury. Three subgroups with different thermosensory profiles showed that the less the damage, the more neuropathic pain occurs. The loss of warm perception in particular might play a pivotal role in the chronicity and severity of subjective sensory symptoms.