The Biopsychosocial Approach
Given that pain affects approximately 50 million Americans, and the costs associated with both the treatment of pain and lost productivity range from $70 to $100 billion annually,1,2 the pursuit for understanding the underlying mechanisms of pain and identifying the best possible treatment options has prevailed because of these staggering costs. Indeed, in a study released by the Centers for Disease Control and Prevention’s (CDC) National Center for Health Statistics,3 one in four U.S. adults reported a pain experience that lasted a full day during the previous month, and 1 in 10 reported an experience of pain lasting a year or more. The study also revealed that one-fifth of adults over the age of 65 reported pain that lasted more than 24 hours, with three-fifths of these older adults reporting that their pain had lasted for more than one year.
Although pain research has traditionally focused on the sensory modalities and the neurological transmissions identified solely on a biological level, more recent theories (integrating the body, mind, and society) have been developed. The most heuristic perspective is known as the biopsychosocial model, with pain viewed as a dynamic interaction among and within the biological, psychological, and social factors unique to each individual. Indeed, as reported by Gatchel,4 Figure 1 presents a conceptual model of these interactive processes involved in health and illness. Pain is not purely a perceptual phenomenon in that the initial injury that has caused the pain also disrupts the body’s homeostatic systems which, in turn, produce stress and the initiation of complex programs to restore homeostasis (to be discussed later in this article). In this paper, we will also examine the following: the evolution of the biopsychosocial perspective from earlier pain theories; the fundamental attributes associated with chronic pain conditions; and the biopsychosocial approach to the assessment and management of pain.
Evolution of the Biopsychosocial Model of Pain
The earliest theories of pain had focused primarily on the understanding of the biological or pathophysiological component of pain. Cartesian Dualism, or separation of the mind and the body, dates back to the 17th century when Rene Descartes conceptualized pain as an exclusive process within the sensory nervous system.5 At that time, diseases and illnesses were described purely as mechanistic biological processes. Even without empirical evidence, it was conceived that the experience of pain was conveyed directly to the brain from the skin, without any psychosocial interplay. Termed biomedical reductionism, this point of view remained constant through the late 19th century. During the late 1800s, two additional theories arose, providing a clearer conceptualization of the biological view of pain. The specificity theory of pain, put forth by Maximilian von Frey in 1894, proposed that there were subcutaneous receptors unique to the different types of sensory input.6 The distinctions between these receptors varied with respect to their functionality, such that they were designed explicitly to allow for the interpretation of sensations such as touch, temperature, pressure, or pain.
The pattern theory of pain, presented by Goldschneider in 1894, differed from von Frey’s theory by stating that, not only were all subcutaneous receptors alike, but the unique patterns of stimulation at the nerve endings were what distinguished the variability in the interpretations of the sensory signals.6 It was assumed that the central nervous system was responsible for coding these nerve impulse patterns that resulted in the pain experience. Although this theory helped to explain incidences of phantom limb pain, which is described as experiencing pain after the termination of the input, the pattern theory of pain disregards receptor and fiber evidence which has come to fruition in recent developments.
Today, there is much more known about the different types and functions of receptors, such that mechanoreceptors respond to touch and pressure, while thermoreceptors activate in response to changes in temperature. Nociceptors are associated with pain perception and, depending on the specific fiber (A, d or C) of the nociceptor type (mechanical, thermo-mechanical, or polymodal) that is stimulated, the perception of pain can range from sharp and prickly, to burning or freezing.7
Although the specificity and pattern theories of pain were fundamental in the development of the understanding of biological modalities, the detachment from this dualistic view corresponded with the lack of integration of mind-body phenomena. The lack of adequate explanations for pain and suffering spurred the next advance in our understanding of nociception and the individual experience of pain. In the 1960s, Melzack and Wall8 postulated a more integrative model—The Gate Control Theory of Pain. Although the underlying mechanisms of this proposed theory are often debated, the implications that there is an interaction between the psychosocial and physiological processes have been widely accepted.5
The gate control theory of pain emphasized the significant role that psychosocial factors potentially play in the perception of pain. The term ‘gate control’ refers to the proposed mechanism of the substantia gelatinosa located in the dorsal horn of the spinal cord. Melzack and Wall8 claimed that this gate-like function modulated the amount of afferent impulses from the periphery to the transmission cells (T-cells) of the dorsal horn through inhibitory processes at the neuronal level, and thereby controlling the quantity and intensity of the signals to the central nervous system. Furthermore, it was posited that higher cortical functions contribute to this gating mechanism. This allows for psychological phenomena to directly affect the subjective experience of pain.
From a clinical perspective, Gatchel5 suggests that the psychosocial component in the gate control theory contributes a great deal in treating patients with pain. Negative states of mind—such as helplessness, hopelessness and anger—tend to amplify the intensity of the sensory input, while strategies focusing on coping and stress reduction help to “close” the gate. Also, behaviors found to facilitate keeping this gate “open” include poor eating habits, smoking, inadequate sleep, and lack of exercise. By promoting positive health behaviors, proactive choices can be factors in lessening the perception of pain.