partially contributed to the establishment of the International Association for the Study of Pain (IASP) (Petrucci et al., 2022). In this regard, the first proposals of the association there were, indeed, centered on the definition of pain and the classification of chronic pain syndromes. These first efforts have contributed to stimulating a worldwide debate on pain terms and classification, which continues today. These first proposals, however, were not without a few controversies. Although there seems to be a general agreement nowadays on the definition of pain, the recognition of pain as a disease remains debated. Based on their duration, different types of pain are currently classified as chronic pain, whose commonly accepted definition is “that pain which persists past the normal time of healing.” However, although this definition has historically been helpful to distinguish between pain as a symptom of an underlying disease and more complex long-lasting pain states, this definition does not identify this condition as a distinct disease state. The roots of the conception of pain as a disease have to be retraced in the work of the pioneers of pain medicine, the medical branch established in the USA in the 1960s to create a specific discipline for the study and management of pain. The leader of this movement, John J. Bonica, distinguishes between normal and abnormal pain based on time and physiology: Pain becomes pathologic when, if persisting, it loses its biological damage signaling function and, with its devastating psychophysiological consequences, becomes a destructive force hard to manage with traditional therapeutic means. Thus, in his perspective, this so-called intractable pain has to be considered a pathologic entity requiring a specific therapeutic approach. Further progresses toward the acknowledgment of the specific nature of persistent pain was made in the 1980s, although this recognition was still based only on the difference in terms of behavioral manifestations between this condition and acute pain in patients and animal test models. In two different studies published in 1980, Pilowski and Sternbach submitted that: “Chronic pain, that is, the pain persisting after the healing of the injury, is different from acute pain because of its pathologic psychobehavioral manifestations.” Another researcher, Doley’s, submission on chronic pain also received wide publicity at this time. Doley described chronic pains as “a set of behaviors or responses to some type of insult or injury that exceeded expectations and extended beyond the normal healing time.” Chronic pain, in Doley’s submission, was that which was “left over after the ‘real’ disease had resolved” (Raffaelli et al., 2021). In the 1990s, a crucial step forward in the definition of pain as a disease was attained. During this period, chronic pain was described as an autonomous entity, not only in opposition to acute pain. In the 1990 edition of The Management of Pain , Bonica devotes an entire chapter to chronic pain and defines it as the pain “which persists a month beyond the usual course of an acute disease or reasonable time for an injury to heal, or pain that recurs at intervals for months or years.” The acknowledgment of the specificity of chronic pain supported an earlier submission published in the 1986 edition of the classification of chronic pain syndromes by the IASP Subcommittee on Taxonomy. The new concept of pain as an autonomous entity gained huge acceptance and developed into a central subject of widespread international debate (Pan et al., 2022). Theories of pain in medical science Beyond merely adopting an acceptable definition for pain, different independent researchers and government-funded projects have developed theoretical frameworks describing the physiology of pain in humans and animal models. In this vein, different theoretical frameworks have been proposed to explain the physiological basis of pain, although none yet completely accounts for all aspects of pain perception. Here, this course provides a historical overview of the major contributions, ideas,
At the Second Congress of the Italian Society of Pain Clinicians held in 1992, Raffaeli proposed an idea that there could not be a system so complex as the endogenous pain system, consisting of several receptors involved, at the neurophysiological level, in the integrative pain modulation without a pathologic counterpart. Raffaelli’s view failed to explain the underlying mechanism of the pathologic counterpart. However, this view recognized pain as an autonomous pathology, that is, a “chronic pain status” characterized by the sole and imperative presence of the pain requiring a therapeutic response (Koesling & Bozzarro, 2022). In 1995, Raffaeli reinforced this view by organizing the ISAL (Istituto di Scienze Algologiche) School—a symposium entitled “Pain as a disease.” The change in the view of chronic pain that occurred in the 1990s was so dramatic that in 1999, Michael Cousins stated that: “chronic pain will be regarded as the disease of the 21st century.” In a 2004 work, Siddall and Cousins further strengthened this view by claiming that chronic pain is a disease with its pathology, symptoms, and signs, based on the pathophysiological changes brought about by pain itself (Butera et al., 2021). In the 21st century, the identification of pain as a disease in its own right is supported by further reflections by pain medicine experts. In a 2004 lecture, John D. Loeser recalls Encyclopedia Britannica’s definition of disease as “an impairment of the normal state of an organism that interrupts or modifies its vital functions” and concludes that since chronic pain certainly does modify functioning, in many different ways, it has to be recognized as a disease in its own right. The efforts in providing a specific biologic characterization of pain as a disease continues in the 21st century when crucial studies revealed the pathologic features associated with persistent pain, especially at the nervous system level. In his 2004 lecture at the Congress of the World Institute of Pain, Ronald Melzack described chronic pain syndromes to be caused as a result of “neural mechanisms gone awry.” In the last decade, significant progress in this field has been made, also thanks to the noteworthy contribution of neuroimaging studies. Compelling evidence of functional, structural, and chemical changes occurring in the brain in association with chronic pain was reported in a 2009 review by Tracey and Bushnell. These submissions support the idea that chronic pain should be classified as a disease state—a condition characterized by a disordered nervous system (Arévalo-Martínez et al., 2022). That same year, the American Academy of Pain Medicine put forward a position paper recommending distinguishing between two categories of pain and proposing a new terminology for pain—eudyinia and maldynia, literally good pain and bad pain. Eudyinia is the pain described as: “a symptom of an underlying pathological disorder, either an illness or an injury.” On the other hand, Maldynia describes pathological pain. This refers to pain as a neuropathological disorder or disease process that occurs due to changes at the cellular and molecular levels (Mayoral Rojals et al., 2022). Today, it is generally regarded that persistent pain entails a pathologic reorganization of the neural system. This process can be due to several factors, such as a genetic predisposition, central sensitization mechanisms, and many other factors, which are at the core of the study of the etiology of pathologic pain conditions (Marchand et al., 2021). and competing theories of pain from ancient civilizations to Melzack and Wall’s gate control theory of pain. This course will explore the different pain theories postulated since the 17th century with a concluding overview of the current thinking on this subject. Arguably, the four most influential theories of pain perception include the specificity (or labeled line), intensity, pattern, and gate control theories of pain (Figure 1).
Book Code: PYFL4024
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