Brain Gray Matter Decrease in Chronic Pain Is the Consequence and Not the Cause of Pain

In a recent publication by Rodriguez-Raecke and colleagues it was reported that regional grey matter losses associated with osteoarthritic pain are reversed following hip replacement and subsequent pain relief. The authors suggest that grey matter changes are a consequence, not the cause of chronic nociceptive pain. Although this is possible, the data presented precludes this interpretation, since the grey matter changes were directly associated with the presence of pain i.e. if pain was perceived, then regional grey matter volumes were reduced. Indeed the most parsimonious explanation is that grey matter changes underlie the perception of pain as when pain was relieved, regional grey matter returned towards control levels in a sub-group of patients. More importantly, the data presented suggests that the changes in regional brain structure associated with chronic nociceptive pain can be reversed if the source of increased afferent drive is stopped. This is an important finding and suggests that future treatment regimes which aim to reverse the anatomical changes associated with other types of chronic pain, such as neuropathic pain, may also be effective at relieving pain.