Chronic Pain : Pathophysiological Mechanisms and Categorization

Abstract

Pain is a common experience that everyone has felt ; however, it can be largely distressing when it persists even after an illness or injury has healed. The International Association for the Study of Pain (IASP) defines chronic pain as pain that lasts for 3-6 months and in cases where pain persists for longer periods, psychological and social factors often play a role in the continuation of pain, in addition to organic factors. Therefore, the WHO and IASP established a classification for chronic pain in ICD-11, with chronic secondary pain syndromes being categorized as those resulting directly from bone and joint or nervous system problems, and chronic primary pain being classified as those that are difficult to explain by organic factors alone, even if organic factors are present. Mechanisms underlying chronic secondary pain syndromes have been elucidated using animal models of neuropathic and nociceptive pain. The clinical categories of chronic primary pain include fibromyalgia, chronic low back pain, irritable bowel syndrome, and glossodynia, which are influenced by diverse nurturing experiences and environmental factors and often involve organic factors to some extent, resulting in the pathophysiology of nociceptive pain. Currently, the mechanisms underlying nociceptive pain disorders are being increasingly elucidated, and exploring the direction of comprehensive treatment is necessary.