Variations in brain volume and regional morphology associated with chronic pain

Various peripheral and spinal mechanisms have been hypothesized to contribute to pain amplification and chronicity. However, the role of the brain in chronic pain states remains to be fully elucidated. Functional brain imaging techniques, such as positron emission tomography and functional magnetic resonance imaging, have frequently been used to investigate brain activity during acute/experimental pain perception, which has helped to establish the notion of the human pain network. In the context of chronic pain, the assessment of brain chemistry (by way of spectroscopy) and brain morphology is of growing interest, and there is a quickly expanding body of evidence that persons with chronic pain conditions, including chronic low back pain, chronic tension-type headache, and fibromyalgia, display changes in global and regional brain morphology. It has been suggested that prolonged nociceptive input to the brain might induce functional and morphologic maladaptive processes that in turn further exacerbate the experience of chronic pain. Alternatively, morphologic changes might predispose toward vulnerability to develop a chronic pain state. The purpose of this review is to examine current literature regarding altered brain morphology in patients with various chronic pain states, summarize these findings, and evaluate their implications for our understanding of the pathophysiology of chronic pain.