Functional neuroimaging suggests that similar brain regions are involved in the processing of pain in healthy subjects and in patients with chronic neuropathic central pain. We present a patient with chronic neuropathic central pain due to a unique lesion to the trigeminal and spinothalamic pathway who had persistent pain relief after repeated IV lidocaine infusions. Positron emission tomography scan results showed a relative hypoactivity of the left posterolateral thalamus before treatment which disappeared after therapy. This case may suggest a stereo-selective analgesic effect of lidocaine accompanied by regional cerebral blood flow changes in the thalamus, indicating that sodium channels could, in fact, be highly expressed or modified in the thalamus after thalamic deafferentation.
Implications: We present a case of persistent central pain after encephalitis in a patient who had long-term pain relief after a series of IV lidocaine infusions. A positron emission tomography scan study, done before and after treatment, suggested that lidocaine for the diagnosis of chronic neuropathic pain may have a specific site of action in the brain.