Trigeminal root dislocation subtends focal demyelination of primary trigeminal afferents in patients with trigeminal neuralgia

Objective: Trigeminal neuralgia (TN) is a neuropathic pain condition associated with focal demyelination of primary trigeminal afferents. Although MRI is routinely used in TN, the specific anatomical abnormality of the trigeminal root that reflects focal demyelination remains unclear. In this combined clinical, neurophysiological and neuroimaging study, we aimed to identify whether specific clinical features and trigeminal root abnormalities predict trigeminal reflex asymmetry, which may reflect unilateral focal demyelination of primary trigeminal afferents. Methods: We retrospectively analysed clinical, neurophysiological and neuroimaging data from 78 patients with primary TN (67 classical, 11 idiopathic). Logistic regression was used to assess whether trigeminal root abnormalities and clinical features predicted trigeminal reflex asymmetry. Reflex asymmetry was defined as latency differences exceeding 0.1 ms between affected and unaffected sides in the early component of the blink or masseter inhibitory reflex, selected according to the trigeminal division involved. Trigeminal root volumes and dislocation were independently assessed by blinded neuroradiologists. Results: Severe trigeminal root dislocation predicted trigeminal reflex asymmetry (p < 0.05). Conversely, trigeminal root atrophy was not associated with asymmetry. Conclusions: This retrospective, clinical, neurophysiological, and neuroimaging study in patients with TN showed that a severe trigeminal root dislocation predicted trigeminal reflex asymmetry. Significance: This suggests that root dislocation may underlie focal demyelination in TN.