Physiological and Psychological Bases of Pain
Dennis C. Turk
University of Washington
Pain has existed since time in memoriam. Perhaps the first documented mention of pain was in the Ebers papyrus dating back to the fourth century B.C. that indicated the use of opium for the treatment of headaches. Since that time, pain has been the focus of philosophical speculation and scientific attention, yet it continues to remain a challenging problem for the sufferer, health care providers, and society.
Pain has been classified in a number of different ways, including the use of a single temporal dimension ranging from acute (momentary pain or pain extending from several hours, days, and weeks) to chronic (persisting over periods of months) to single categorical systems, such as presumed etiology (e.g., neuropathic, somatic, psychogenic), to more multiaxial diagnoses in which multiple factors are included in the classification (e.g., location, system involved, temporal characteristics and pattern of occurrence, intensity, and etiology; Merskey, 1986). For s implicity this chapter uses a categorical approach referring to four c ategories of pain: acute, acute recurrent (e.g., migraine headache), chronic nuncancer pain (e.g., low back pain), and pain associated with a malignant disease process (i.e., cancer).
Pain is essential for survival because of its alarm function. In acute pain states, nociception (activation of sensory transduction in nerve fibers that convey information about tissue damage) has a definite purpose, it acts as a warning signal that requires immediate attention, reflexive withdrawal, and other actions in order to prevent further damage and to facilitate the healing process. In chronic pain states, this adaptive function plays a significantly smaller role and can often no longer be discerned. In the case of recurrent acute pain diagnoses, such as migraine headaches, the role of pain is even less clear because there is no protective action that can be taken or any tissue damage that can be prevented. Pain associated with neoplastic disease has some features in common with acute pain in that it may be a warning signal; whereas in others it is more like chronic pain because the pain may serve no purpose.
Pain is a common symptom in people who seek medical assistance accounting for over 70 million office visits to physicians each year (National Center for IIealth Statistics, 1986). Each of the four pain categories are extremely prevalent. Consider a sample of some available statistics. Over 23 million surgical procedures were performed in the United States in 1989 (Peebles & Schneidman, 1991) and most of these involved acute pain. Acute recurrent and chronic pain affect over 70 million Americans, with over 10% reporting the presence of pain over 100 days/year (Osterweis, Kleinman, & Mechanic, 1987). Estimates suggest that over 11 million Americans suffer from recurring episodes of migraine headaches (Stewart, Lipton, Celentano, & Reed, 1991), over 30 million experience chronic or recurrent back pain (IIolbrook, Grazier, Kelsey, & Staufer, 1984), and 37 million have pain associated with arthritis (Lawrence et al., 1989). Approximately 3.5 million people in the United States have cancer (Raj, 1990). Bonica (1979) estimated that moderate to severe pain is reported by from 40% to 45% of patients initially following the diagnosis, from 35% to 45% at the intermediate states of the disease, and from 60% to 85% in advanced states of the cancer.
Given the. lengthy history of pain and the statistics on its prevalence, it might be assumed that pain is well understood and readily treated. Despite advances in the understanding of anatomy and physiological processes and innovative and technically sophisticated pharmacological, medical, and surgical treatments, pain continues to be a perplexing puzzle for health care providers and a source of significant distress for