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.