Neuroimaging Chronic Pain: What Have We Learned and Where Are We Going?

Katherine T Martucci; Pamela Ng; Sean Mackey

Disclosures

Future Neurology. 2014;9(6):615-626. 

In This Article

Abstract and Introduction

Abstract

Advances in neuroimaging have helped illuminate our understanding of how the brain works in the presence of chronic pain, which often persists with unknown etiology or after the painful stimulus has been removed and any wounds have healed. Neuroimaging has enabled us to make great progress in identifying many of the neural mechanisms that contribute to chronic pain, and to pinpoint the specific regions of the brain that are activated in the presence of chronic pain. It has provided us with a new perception of the nature of chronic pain in general, leading researchers to move toward a whole-brain approach to the study and treatment of chronic pain, and to develop novel technologies and analysis techniques, with real potential for developing new diagnostics and more effective therapies. We review the use of neuroimaging in the study of chronic pain, with particular emphasis on magnetic resonance imaging.

Introduction

Chronic pain is a widespread and growing problem in the USA, affecting more than 100 million adults at some point in their lives, and accounting for about US$600 billion annually in medical costs and lost productivity.[1]

Chronic pain is complex, and the neural mechanisms that underlie chronic pain have been poorly understood. However, the evolution of various neuroimaging techniques has opened new windows into the brain and spurred new avenues of pain research that hold real promise for developing new, more effective treatments. Neuroimaging has shown us that chronic pain is different from acute pain, and that it can become a separate disease entity that may occur, in part, following changes in the entire CNS that cause chronicity and the development of comorbid symptoms. However, it is imperative to remember that despite the involvement of brain changes in chronic pain, the nervous system is not solely responsible for the initiation and/or maintenance of chronic pain, as addressed in a series of recent commentaries.[2,3]

Nonetheless, neuroimaging has become an increasingly important and popular means of studying how the brain perceives and processes chronic pain. Various neuroimaging modalities have been used, including PET, EEG,[4] magnetoencephalography (MEG), single-photon-emission computed tomography (SPECT/CT)[5] and MRI. These techniques have been used to study several chronic pain states, including, most commonly, chronic low back pain (cLBP),[6] fibromyalgia (FM),[7] osteoarthritis,[8] complex regional pain syndrome (CRPS),[9,10] phantom-limb pain, chronic migraine,[11] chronic pelvic pain (CPP)[12,13] and peripheral neuropathy,[14] among others.[15] Experiments have evaluated acute pain processing mechanisms in healthy volunteers[16–18] and in animals[19] and in animal models of chronic pain.[20] Neuroimaging has helped elucidate many of the neural correlates regarding factors well known to modulate the experience of pain, including attention,[21] anticipation,[22] empathy,[23,24] placebo,[25] meditation,[26] fear/anxiety[18] and reward.[15] Each factor impacts how we perceive pain, and an increasing number of functional neuroimaging studies are investigating how these factors affect pain perception and activity in the brain. Current pain research also uses various neuroimaging techniques to investigate a broad range of translational science that can eventually be tested in clinical trials.

The present review focuses specifically on the use of neuroimaging, and especially MRI, to study CNS changes in patients with a variety of chronic pain states.

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