Chronic pain is an extremely complex and debilitating problem that presents itself in many ways in modern-day society. While there is clearly a biological substrate to chronic pain, there are also societal, psychosocial, financial, political, and public health components that bring far-reaching implications to research, diagnosis, and treatment of chronic pain disorders.
Remarkable advances in understanding pain and providing improved treatments have come through scientific discoveries, improved training and access to specialized clinics, organizations, national agendas, and industry and advocacy groups. However, our clinical armamentarium is relatively limited in providing relief in chronic pain conditions. In the past, the basic therapy has included, for the most part, (1) drugs, mostly belonging to three classes—opioids, nonsteroidal anti-inflammatory drugs, and local anesthetics; (2) interventional treatments; (3) psychological biobehavioral therapy; and (4) some adjuvant medications, as well as complementary and alternative therapies. For all of these efforts, the number of outcome studies of nonpharmacological trials is limited, and most pharmacological studies show poor efficacy of treatment in chronic pain.1 Pain researchers, pharmaceutical companies, and clinicians have struggled to break the barriers of finding treatments for pain that are both specific and efficient and have limited side effects.
Part of the problem we have faced is a new realization that chronic pain is a disease of the brain. Until recently, there has been a lack of ability to measure changes in the brain that are a consequence of chronic pain. Anatomic, functional, and chemical neuroimaging have opened the door to new vistas and new opportunities for a better understanding of chronic pain, better diagnostic possibilities, and, perhaps, better drug treatments to be developed. Although genetic and other molecular approaches in the pain field have shown tremendous advances, only in recent years has brain imaging contributed to the revolution in understanding pain, greatly changing the field of pain research.
The major insight that emerged from neuroimaging studies is that chronic pain is a disease of the brain, and, thus, all therapeutic modalities will need to take this into consideration. The ability to explore the human brain in human volunteers or patients has dramatically changed our understanding of pain. Imaging has the ability to define theoretical constructs of numerous thinkers in the field of brain processing in chronic pain in the human condition. Imaging has allowed unprecedented interrogation of brain systems in terms of brain circuitry, the effects of analgesics on neural networks, transition of acute into chronic pain, definition of brain regions that heretofore may not have been considered important (e.g., nucleus accumbens, striatal regions), brain plasticity including functional and morphological changes, networks that are involved in the placebo response, and alterations in neurochemistry in chronic pain (Fig. 12-1).
Placebo response and alterations in neurochemistry in chronic pain. (From Sava et al., The pain imaging revolution: advancing pain into the 21st century. Neuroscientist. 2010;16:171-185.)