Structural brain imaging: a window into chronic pain.

Structural imaging is turning our attention regarding the effects of chronic pain on the brain as a possible source of chronicity. Several independent studies have suggested a decrease in gray matter in pain-transmitting areas in patients with constant pain. Most of these data are discussed as representing damage or loss of brain gray matter, reinforcing the idea of chronic pain as a progressive disease. However, any data of an increase or decrease in gray matter in pain syndromes need to be considered in light of all observations gathered in the past 10 years and probably do not justify a discussion of brain damage or consideration of whether the disease is progressive. It is likely that these changes are the consequence and not the cause of the respective pain syndromes as they may reverse once the pain is adequately treated. Moreover, structural changes of the brain may not be specific to a particular pain syndrome and for the moment only mirror the magnitude or duration of pain suffered. The topographical distributions of gray matter changes may well be the consequence of cortical regions having varying susceptibilities. We need to better understand the behavioral consequences and cellular mechanisms underlying these neuroanatomic changes.