Quantitative Sensory Testing Identifies Altered Thermal and Pain Processing in Trigeminal Neuralgia

Introduction: This cross-sectional study aims to assess somatosensory function in patients with trigeminal neuralgia (TN) using quantitative sensory testing (QST) and QST-based sensory phenotyping, and to investigate their relationship with clinical findings, including etiology (classical and idiopathic TN), type of pain (paroxysmal pain only and concomitant continuous pain), and response to pharmacological treatment. Methods: Sixty-five patients with classical or idiopathic TN underwent QST. Sensory alterations were quantified using z-scores derived from normative data, and sensory profiles were identified using a validated algorithm. Clinical characteristics, presence of concomitant continuous pain, and response to first-line sodium channel blockers were systematically recorded through a structured questionnaire. Results: QST showed bilateral thermal hypoesthesia and pain hyperesthesia in the whole patient population. Cold detection threshold (CDT) was significantly reduced on the affected side compared to the unaffected side in patients with Classical TN. Idiopathic TN was associated with bilaterally elevated wind-up ratio. Patients with purely paroxysmal pain showed a bilateral gain of function in heat pain thresholds. Sensory phenotyping identified mechanical hyperalgesia (49%) and thermal hyperalgesia (35%) as predominant phenotypes. A sensory loss phenotype was significantly associated with poor response to sodium-channel blockers. Discussion: TN is characterized by subtle and complex bilateral sensory alterations, potentially suggesting central modification of sensory processing. The finding of asymmetrical CDT reduction may indicate peripheral Aδ-fiber dysfunction. Sensory profiling may identify subgroups with distinctive treatment responses, with sodium channel blockers being less effective in sensory loss phenotype.