Chronic pain is a widespread, debilitating condition shared by millions worldwide. In 2015, more than 25 million Americans reported suffering from consistent daily pain.1 The Center for Disease Control (CDC) reported 15.6% of American adults experience consistent headaches or migraines, 29% have consistent low back pain, and 14.9% suffer consistent neck pain. With pain conditions accounting for approximately 80% of doctor visits, effective pain management and prevention methods are essential to use in order to effectively deal with issues such as emotional distress, loss of workproductivity, and quality of life in these patients.2 The US spends roughly $625 billion annually for medical treatment and lost productivity related to the pain conditions.2,3
The prevalence of chronic pain stimulated the US Congress to designate that the 2000s would be the decade of pain control and research,3 by passing “The 2010 Patient Protections and Affordable Care Act.” Moreover, the National Institutes of Health (NIH) supported the Department of Health and Human Services (HHS), in collaboration with the Institute of Medicine (IOM), highlighted the importance to examine pain as a public health issue.2 The IOM’s role was to assess the state of science regarding education, care, and research of pain, to make recommendations about how to proceed forward in the best interest of the public. The IOM presented their findings and recommendations in the US in a publication entitled “Relieving Pain in America: A Blueprint for Transforming Prevention, Care, Education, and Research”.4 The IOM recommendations were: to shift the view of pain from a patient perspective to one of a major public health issue; increase awareness of the problem of pain; focus on the prevention of pain; improve pain assessment techniques; address disparities among sufferers; and foster both treatment centers and cohesive research among scientists and healthcare providers. Interdisciplinary research is essential to better understanding complex, multifaceted issues of pain in order to address these recommendations.5
Individuals experience pain in a multitude of ways, often seeming subjective to the individual based on their perceptions and descriptions of their condition. The variations in how patients perceive and relay this information can influence physician interpretation and treatment strategies. Unfortunately, difficulties in assessing and treating pain have led to an enormous proportion of sufferers to be treated with opioid medications, which manage pain but do not resolve the condition. Opioids tend to be highly addictive, and are often misused. In 2014, The National Institute on Drug Abuse (NIDA) estimated 26–36 million people would abuse opioids globally in the next year.6 Opioid medications cause changes in brain chemistry that can lead to mood and behavioral issues and disrupt physiological functions.7 Treatment models focusing on prevention and early intervention may help decrease the number of patients who require long-term use of opioids. Of course, it is often difficult to establish effective generic pain management programs because every individual displays a unique combination of biopsychosocial factors.3 This is the major reason why the biopsychosocial model, out of which grew interdisciplinary pain management, has been so successful. Additionally, programs that emphasize early intervention and functional rehabilitation components have been shown to be highly effective and financially sensible.3 Reliable conceptual models to gauge individual differences, and then treat them accordingly, are vital to successful pain management.
Conceptualizing chronic pain — an overview
Chronic pain is characterized by persistent symptoms, often unrelenting and debilitating in nature. The definition of pain encompasses unpleasant experiences, both physical and emotional, with actual or potential tissue damage and the chronicity is implied that the pain persists over time.8,9 Where some conditions are acute, and the pain dissipates once the problem is addressed, chronic conditions require ongoing monitoring, treatment, and often require a variety of strategies to manage them. Pain management techniques have been evolving over the course of history; a few notable practices based on such techniques include the Ancient Greeks’ humoral theory, the religious and spiritual ideations of the Middle Ages, and scientific advancements occurring during the Renaissance.10 The resulting theories relied heavily on biological explanations of pain, and incorporated illness, disease, and eventually the individual circumstances and states of the patient.
The biomedical model
The biomedical model explains illness based on somatic processes within the body. This view often assumes that psychological and social processes are largely irrelevant to biological illnesses and focuses instead on mainly biochemical imbalances and neurophysiological abnormalities. However, over the years, even with the ever-increasing number of sophisticated diagnostic and therapeutic procedures (e.g., medical imaging, and interventional/surgical techniques), there has been no solid, objective validation of their effectiveness concerning chronic low back pain.11 Moreover, this promoted unrealistic “high expectations” on the part of patients that this new medical technology would “cure” their pain. Unfortunately, this is not always the case as many chronic conditions require lifelong maintenance (as explained by Gatchel 200512).
The rise of psychosomatic medicine somewhat curbed this strictly biological view and uncovered the important connections between biological and psychosocial factors. Landmark studies started to appear in the scientific literature, such as: Selye 1950,13 who examined the link between homeostasis breakdown and stress; Rosenman and colleagues,14 who examined the link between Type-A behavior and coronary heart disease; and Birk,15 who applied biofeedback techniques to conditions such as headaches. Such studies were crucial in amassing support to move from a strictly biomedical model. Psychodynamically oriented professionals also began to emphasize the role of psychological factors such as personality, attitude, and resilience in illness.16 However, this psychodynamic model remained limited in scope, due to the unstructured, subjective nature of it. The aforementioned shortcomings of methodology and limited range and scope of explanation, coupled with significant advances in neuroscience, and increased attention to eastern medicine practices, “opened the door” for a shift to a better model.
The biopsychosocial model
The biopsychosocial model evaluates the integrated “whole person,” with both the mind and the body together as interconnected entities, recognizing biological, psychological, and social components of pain and illness. Prior to the major research of the biopsychosocial model in the 70s and 80s, pain was generally viewed as an organic process. If pain was not organic, patients were referred for psychiatric care to treat the pain, which was deemed “psychogenic” in nature. The biopsychosocial model also emphasizes illness and how you live with, or respond to, symptoms or a disease, in contrast to the biomedical disease model, which primarily focuses on disruption of bodily systems by underlying physiological, anatomical, or pathological processes. Basically, the biopsychosocial model takes into account the dynamic interactions among bio, psycho and social factors in the pain-experience process.5,8 However, in order to continue to provide effective pain management approaches, the model must adapt as our knowledge and technology advances. Some criticize the biopsychosocial model pointing out that we now expect behavior to be rooted in biological and psychological components, realizing a systemic approach as opposed to the interactions made among these three factors the model historically suggests.17 Expanding the basis for a holistic approach to pain management is necessary, particularly when discussing the need for interdisciplinary assessment and treatment of chronic conditions. There are also often individual differences in the nature of these interactions, which account for the unique symptom patterns presented by specific patients. This creates the need to tailor interdisciplinary pain management programs for each specific patient during the assessment-treatment process.
George Engel’s conceptual model of illness suggested a progression of pain stemming from a physical problem, to distress, then illness behavior, and finally adoption of a sick role (Figure 1) thus incorporating bio, psycho, and social components.18 Engel studied patients with medical disorders, finding that biological measures alone did not provide a comprehensive view of the patients’ pain and treatment, and needed to consider psychological, social, and cultural factors to accurately assess and manage illness conditions.3 Engel felt previous pain theory had overlooked the critical interaction of multiple factors and sought to develop his own to address the gaps not addressed by biomedical models.18 Loeser proposed a direct model of pain in which a physiological component (nociceptors), as the beginning of the pain progression, as seen in Figure 1.19 According to Loeser’s theory, nociceptors are sensory nerve cells that respond to damage within the body through a process called nociception. The stimulation of the nociceptors leads to a sensory component (i.e., experiencing physical pain). This process results in affective components, suffering, and exhibition of pain behaviors. Pain behaviors are acts used to communicate feelings associated with the pain experience. Suffering refers mainly to the emotional distress caused by pain. These emotions typically manifest internally, and are often highly unpleasant. Though central components of Loeser’s model are no longer accepted, his model is often discussed as an important historical concept that helped develop our current understanding of pain conditions.
Melzack and Wall’s Gate Control Theory of Pain was the initial basis for our current modern understanding of pain physiology.20 This theory aimed at a more comprehensive explanation of pain by melding
specificity theories with affective views and pattern-response theories.5 The Gate Control Theory, presented in a series of stages, proposed the dorsal horn of the spinal cord acted as a gate that modulated sensory transmissions controlled by pain and touch fibers before reaching higherlevel brain areas for perception.16 Building from the Gate Control Theory, the Neuromatrix Theory of Pain (originally proposed by Melzack and Casey21), describes a network involving motivational-affective, cognitiveevaluative, and sensory-discriminative functions. The combinations of these components gauge bodily responses to stress. This neural network, called the body-self neuromatrix, suggests that processing of pain is widely distributed throughout the neuromatrix, and the experience of pain results from such output.22