Unilateral decrease in thalamic activity observed with positron emission tomography in patients with chronic neuropathic pain.

The oxygen-15 water bolus positron emission tomography (PET) method was used to image regional brain activity in 4 patients with chronic post-traumatic neuropathic pain confined to one lower limb and in 1 patient with post-herpetic neuralgia. In comparison to 13 normal subjects, scans of the patients disclosed a statistically significant decrease in thalamic activity contralateral to the symptomatic side. Examination of the right/left ratio for all the subjects showed that the values for the patients fell at the extremes of the normal range, according to the side of the affected body part. These initial observations suggest that functional alterations in thalamic pain processing circuits may be an important component of chronic neuropathic pain.