as multiple sclerosis [MS], trigeminal neuralgia, Parkinson’s disease, complex regional pain syndrome [CRPS], por- phyria, systemic lupus erythematosus, lumbar radicular pain, migraines, and cluster headaches). 1 • Nociceptive pain is the normal response to any type of stimulus that results in tissue damage and includes visceral and somatic pain. 14 Examples of nociceptive or inflammatory pain include postoperative pain, osteoarthritis, mechanical low back pain, sickle cell crises, and pain from traumatic injuries. ° Somatic pain, whether superficial or deep, is nociceptive pain that results from issues within the body’s bone, joints, muscles, skin, or connective tissue; it may be localized and stabbing, aching, and/or throbbing. 14 Examples include mechanical low back pain, osteoarthritis, and muscle sprain or strain. • Neuropathic pain results from damage to or Visceral pain is nociceptive pain that arises from the body’s organs and may be cramping, throbbing, and/or vague. 14 Examples are pain related to myocardial infarction, pancreatitis, or cholecystitis. ° abnormal processing of the CNS or peripheral nervous system and may be sharp, stabbing, burning, tingling, and/or numb. 14 Certain neuropathic pain conditions may be diagnosed as chronic pain before the three-month mark. 23 Examples include diabetic neuropathy, regional pain syndrome, or trigeminal neuralgia.
Pain Definitions
Pain Classifications
The International Association for the Study of Pain (IASP) revised its pain definition in 2020 to better convey pain’s nuances and complexities and to improve its assessment and management. The IASP defines pain as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.” 21 The IASP further describes pain as follows: 21 • As a personal experience that is influenced to varying degrees by biological, psychological, and social factors • As a separate phenomenon from nociception that cannot be inferred solely from activity in sensory neurons • As a concept learned through the life experiences of individuals • As an experience that should be respected • As serving an adaptive role that may, nonetheless, have adverse effects on function and social and psychological well-being • As existing independently of the ability to express its presence verbally, i.e., verbal description is only one of several behaviors to express pain, and inability to communicate does not negate the possibility that a human or a nonhuman animal experiences pain There are no precise clinical markers for pain, which is experienced by the individual as a constellation of biological, psychological, and social factors that include race and ethnicity (Figure 2). 1 This biopsychosocial model is now preferred to an earlier era’s biomedical model of pain care, which primarily aimed medical, procedural, and surgical treatments at a presumed biological pain generator in an attempt to fix or numb pain. 20 Given pain’s complexity, it is important to perform a thorough patient evaluation so that the presumed or differential diagnosis is accurate in order to select the best therapeutic option. 1 Pain is protective and essential for survival when understood as a warning signal that something has gone wrong in the body. However, when pain persists indefinitely the central nervous system (CNS) begins to sense, transmit, modulate, and interpret the pain experience differently. 14 When the nociceptors, or sensory receptors, become sensitized, they discharge more frequently. In peripheral sensitization, this state of heightened neuron excitability occurs at the site where the pain impulse originated in the body; in central sensitization, it occurs in the spinal neurons, which begin to fire spontaneously, resulting in pain that intensifies and lasts far longer than the stimulus applied. 14 Sensitization can result in hyperalgesia, where response to pain-causing stimuli is intensified, and allodynia, a pain response to stimuli that normally are not painful. 14 Therefore, the resulting pain comes not just from an injury site but from neural impulses. The pathologies created by central sensitization can persist and continue to generate pain impulses indefinitely, far outlasting pain’s usefulness as a warning signal.
Pain can be categorized in several ways, including by type, duration, etiology, and pathophysiology. • Acute pain is a physiologic response to noxious stimuli with a sudden onset and expected short duration. 1 It commonly occurs as a result of burn, trauma, musculoskeletal and neural injury, and after surgery or other procedures in the perioperative period. 1,20 Acute pain flares may also occur periodically in the course of chronic pain and medical conditions. 1 Anxiety and distress may exacerbate the acute pain experience. 22 • Chronic pain lasts longer than normal healing and is generally diagnosed after persisting or recurring for longer than three-to-six months. 14 °
Chronic pain’s many possible causes include injuries, malignancies, chronic diseases, medical treatments or surgeries, or inflammation that appears as a result of injury or chronic disease. Chronic pain may occur in the absence of a defined injury or cause. Anxiety, depression, and stress are known to complicate the chronic pain experience. 1 Chronic relapsing pain conditions have periods of remission and frequent re- lapses (e.g., various degenerative, in- flammatory, immune-mediated, rheuma- tologic, and neurologic conditions such
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Figure 2. The Biopsychosocial Model of Pain 1
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