This article is a historical introduction and overview of the pathophysiology and management of pain. Some of the current concepts of the pathomechanism of pain are described as a basis for the development of new approaches for management. This review will be a useful guide for the practicing physician when sorting out and categorizing various pain problems for further investigation and management. Commonly used drugs as well as nonpharmacological approaches, including surgical procedures for the management of intractable pain, are listed.
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• Pain is an important symptom of neurologic disorders.
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• Management of chronic pain, particularly neuropathic pain, is a challenge.
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• An understanding of the pathomechanisms of various types of pain is helpful in developing a management strategy.
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• Treatment of chronic pain is multidisciplinary and requires a choice as well as a combination of various methods for a personalized approach.
Historical note and terminology
Definitions. Pain is generally defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. Pain can be acute or chronic. Acute nociceptive pain due to inflammation can also become chronic inflammatory pain. Further definitions are used for special types of pain. Terminology is covered further in other MedLink Neurology articles on pain: chronic pain, central neuropathic pain, phantom limb pain, and cancer pain.
Pain in antiquity. In ancient societies, pain was thought to be a result of external magical forces. Ayurvedic medicine in India included the use of herbals as analgesics, and acupuncture was used for relieving pain in ancient China. Aristotle (384 BC to 322 BC) theorized that pain was the opposite of "pleasure" and apart from the traditional "5 senses." The use of natural electricity for pain was documented in the first century. Intractable headache was treated with the discharge of the organ of electric fishes.
Understanding of the basic mechanisms of pain. In the 18th century, Erasmus Darwin started an analysis of "unpleasantness" and attributed pain to overstimulation of 1 of the 5 senses (03). The relation of pain to peripheral injury had already been recognized some years earlier. The difference between touch and pain as sensations of the skin and other organs was pointed out by Weber in the 19th century (39). In the last decade of the 19th century, Henry Head established the referral of pain to the skin from a deep lying structure (ie, the occurrence of arm pain following stimulation of the pericardium) (11). Head’s studies of herpes zoster led to the discovery of segmental distribution of sensory nerves.
Pain in the 20th century. Several scientific studies of the anatomy and physiology of pain in the first half of the 20th century have been summarized in a book by Hardy and colleagues (10). Palliative neurosurgery for relief of pain started during this period. Until the 1960s, pain was regarded as an inevitable sensory response to tissue damage. Tremendous advances took place concerning the understanding and management of pain in the last few decades of the 20th century. In 1964, the Melzack-Wall gate theory emphasized the mechanisms in the central nervous system that control the perception of a noxious stimulus and, thus, integrate afferent impulses with downstream modulation from the brain (24). Discoveries in molecular biology and electrophysiology of pain continue, and the opioid receptors were identified in 1973. A cure for pain, however, has not yet been discovered.
Role of the neurologist in the management of pain. The neurologist is increasingly involved in the multidisciplinary treatment of patients with chronic pain, and neurologic pain management is now recognized as a subspecialty of neurology by the American Board of Psychiatry and Neurology. The American Academy of Neurology recognizes the undertreatment of patients with chronic nonmalignant pain and provides clear recommendations to help neurologists in the ethical and effective treatment of patients with pain.