Evaluation of the pathophysiology of classical trigeminal neuralgia by blink reflex study and current perception threshold testing

We recruited 49 patients with classical trigeminal neuralgia (TN) according to the latest guidelines of the International Classification of Headache Disorders, and divided them into an acute (≤30 days onset; 13 patients) and a chronic (>30 days onset; 36 patients) group. We used blink reflex study and current perception threshold (CPT) testing to evaluate the painful facial areas and contralateral non-painful areas of patients with classical TN. CPT 5 Hz examinations, which correlate with unmyelinated fiber function, showed significantly decreased CPTs in the acute stage (11.62 ± 6.99 vs. 18.69 ± 9.66, P = 0.025), but significantly increased CPTs in the chronic stage (26.67 ± 18.65 vs. 19.69 ± 13.70, P = 0.010) on the painful side when compared with the contralateral non-painful side. However, CPTs at 250 Hz (Aδ) and 2000 Hz (Aβ) examinations did not show significant differences between the painful and non-painful sides. In contrast, only three (3/49) patients showed an abnormal trigeminal nerve stimulation on the ipsilateral painful side by blink reflex study. The findings suggest that classical TN is not a simple large-myelinated nerve fiber dysfunction but a more complex process with a main dysfunction of unmyelinated nerve fibers.