Relief of Trigeminal Neuralgia after Percutaneous Retrogasserian Glycerol Rhizolysis Is Dependent on Normalization of Abnormal Temporal Summation of Pain, without General Impairment of Sensory Perception

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Abstract
This study was undertaken to examine the pathophysiological mechanisms of trigeminal neuralgia and the mechanisms underlying pain relief after percutaneous retrogasserian glycerol rhizolysis (PRGR). Quantitative examination of sensory and pain perception was performed in the trigger area and the contralateral nonpainful facial skin area for 39 patients with trigeminal neuralgia who had been previously treated with PRGR and for 14 non-surgically treated patients. In a prospective study, 9 of the 14 patients were examined before and 4 to 6 weeks after PRGR. In the trigger area of patients who had been previously treated with PRGR for trigeminal neuralgia, we demonstrated increased temperature and tactile thresholds in pain-free patients and in patients with paroxysmal or continuous pain. Abnormal temporal summation of pain (characterized by progressive increases in pain intensity, with radiation of pain and aftersensation) was present in patients with paroxysmal or continuous pain but not in pain-free patients. In the trigger area of non-surgically treated patients with trigeminal neuralgia, we demonstrated significantly increased temperature and tactile thresholds and the presence of abnormal temporal summation of pain. The prospective study showed that pain relief after PRGR was associated with normalization of abnormal temporal summation of pain, without increased sensory loss. Partial deafferentation, with impairment of thin (C/Afi) and thick (A/3) fiber-mediated sensations and abnormal temporal summation of pain, is present in the trigger area of patients with trigeminal neuralgia. Relief of pain after PRGR depends on the normalization of abnormal temporal summation of pain, which is independent of general impairment of sensory perception. Assessment of the temporal summation of pain may serve as an important tool to record central neuronal hyperexcitability, which may play a key role in the pathophysiological changes in trigeminal neuralgia.