Advances in brain imaging of neuropathic pain

To review the literature on the use of brain imaging, including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), magnetic resonance spectroscopy (MRS) and voxel-based morphometry (VBM) in investigation of the activity in diverse brain regions that creates and modulates chronic neuropathic pain.

English literatures from January 1, 2000 to July 31, 2007 that examined human brain activity in chronic neuropathic pain were accessed through MEDLINE/CD ROM, using PET, fMRI, VBM, MRS and receptor binding.

Published articles about the application of fMRI, PET, VBM, MRS and chronic neuropathic pain were selected.

Data were mainly extracted from 40 representative articles as the research basis.

The PET studies suggested that spontaneous neuropathic pain is associated with changes in thalamic activity. Both PET and fMRI have been used to investigate the substrate of allodynia. The VBM demonstrated that brain structural changes are involved in chronic neuropathic pain, which is not seen in a matched control group. However, the results obtained had a large variety, which may be due to different pain etiology, pain distribution, lesion tomography, symptoms and stimulation procedures.

Application of the techniques of brain imaging plays a very important role in the study of structural and functional reorganization in patients with neuropathic pain. However, a unique "pain matrix" has not been defined. Future studies should be conducted using a prospective longitudinal research design, which would guarantee the control for many confounding factors.