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Explore the definition, history, and theories of pain, its impact on health, and factors influencing perception. Learn about nociception, pain thresholds, and the body's response to injuries. Discover how pain affects life quality and its implications.
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PAIN Liliana Tarţău, MD, PhD
Definition of pain (IASP) An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Pain is subjective. Each individual learns the meaning of the word "pain" through experiences related to injury in early life. Biologists recognize that those stimuli or illnesses that cause pain are likely to damage tissue.
History The ancient Greek believed that pain was associated with pleasure because the relief of pain was both pleasurable and emotional. The Romans, coming closer to contemporary thought, viewed pain as something that accompanied inflammation. - 2nd century, Galen offered the Romans his works on the concepts of the nervous system. - 4th century, successors of Aristotle discovered anatomic proof that the brain was connected to nervous system. - Aristotle’s belief prevailed until the 19th century, when German scientist provided irrefutable evidence that the brain is involved with sensory and motor function.
History Modern concepts of pain theory continue to advance from the ideas of Aristotle. However, controversy still exists as to which theories are correct. The theories accepted at the turn of the century were the specificity theory and the pattern theory, two completely different and seemingly contradictory views. The specificity theory suggests that there is a direct pathway from peripheral pain receptors to the brain. Proposed by Ronald Melzack and Patrick Wall during the early 1960s, gate control theory suggests that the spinal cord contains a neurological "gate" that either blocks pain signals or allows them to continue on to the brain. Unlike an actual gate, which opens and closes to allow things to pass through, the "gate" in the spinal cord operates by differentiating between the types of fibers carrying pain signals.
General data • Pain is a conscious experience that results from brain activity in response to a noxious stimulus and engages the sensory, emotional and cognitive processes of the brain. In general terms we can distinguish two dimensions or components of pain: • sensory - discriminative • affective - emotional. • Nociception is the process by which information about a noxious stimulus is conveyed to the brain. It is the total sum of neural activity that occurs prior to the cognitive processes that enable humans to identify a sensation as pain. Nociception is necessary but not sufficient for the experience of pain.
General data • pain threshold – level of noxious stimulus required to alert an individual of a potential threat to tissue. • pain tolerance – amount of pain a person is willing or able to tolerate.
General data Pain is a major health issue. • The number one cause of adult disability in the US; • Prevalence of chronic pain in the general population is estimated at 116 million people. • Pain costs an estimated $560 to $635 billion annually in lost workdays, medical expenses, and other benefit costs.
General data Pain diminishes the quality of life for many people, although it may also be a vital teacher or a warning message to be heeded. How humans process pain is a complicated, individualized process affected by genetics, personality, life experiences and straightforward physiological processes. When an injury disrupts homeostasis, and depending upon the extent and severity of the injury, genetically predetermined neural, hormonal, and behavioral programs kick into action.
General data The body’s response is as follows: The injury triggers a process by which sensory information is relayed rapidly to the brain, which initiates the complex sequence of events to reinstate homeostasis. The body releases cortisol, a hormone produced by the adrenal glands, in an effort to re-establish homeostasis. Cortisol produces and maintains high levels of glucose for quick response following an injury, threat, or other form of emergency (such as the fight or flight response).
General data Negative consequences of pain • decreased socialization • withdrawal from daily life • fatigue • sleep disturbance • irritability • physical deconditioning • stress • depression.
Congenital analgesia A well-known case of congenital insensitivity to pain is a girl referred to as 'miss C' who was a student at McGill university in Montreal in the 1950s. She was normal in every way, except that she could not feel pain. When she was a child she had bitten off the tip of her tongue and had suffered third-degree burns by kneeling on a radiator, When she was examined by a psychologist she did not feel any pain when she was given strong electric shocks or when exposed to very hot and very cold water. When these stimuli were presented to her she showed no change in heart rate, blood pressure or respiration.
Implications for clinical practice • There is no physiological, imaging, or laboratory test that can identify or measure pain. Pain is what the patient says it is. The clinician must accept the patient's report of pain. • The goal of pain therapies is to relieve pain whenever possible: from nociception to the conscious experience as well as to decrease the emotional response to the unpleasant experience. Nociception should be treated even in unconscious patients who appear to be clinically unresponsive to pain to help prevent sensitization of pain pathways which can lead to chronic pain.
General data Pain has a biologically important protective function. The sensation of pain is a normal response to injury or disease and is a result of normal physiological processes within the nociceptive system, with its complex of stages previously described. There may also be other manifestations of pain related to tissue injury including hyperalgesia, an exaggerated response to a noxious stimulus, and allodynia, the perception of pain from normally innocuous stimuli. Hyperalgesia and allodynia are the result of changes in either the peripheral or central nervous systems, referred to as peripheral or central sensitization, respectively.
General data Pain is a multidimensional phenomenon which is an attention grabbing sensation that can produce strong emotional reactions that adversely affect a patient's function, quality of life, emotional state, social and vocational status, and general well-being. Therefore, pain assessment should also be multidimensional. It is important to evaluate these various elements during the interview and examination, and include them in the diagnostic formulation.
General data A thorough history and physical exam are essential for the medical and pain diagnosis and treatment planning. A pain history should include location, quality, intensity, temporal characteristics, aggravating and alleviating factors, impact of pain on function and quality of life, past treatment and response, patient expectations and goals. Careful attention to the patient's reported symptoms will help direct the physical examination and narrow the pain differential diagnosis.
Classification of pain - based on pain physiology, intensity, temporal characteristics, type of tissue affected, and syndrome: • pain physiology (nociceptive, neuropathic, inflammatory) • intensity (mild-moderate-severe; 0-10 numeric pain rating scale) • time course (acute, chronic) • type of tissue involved (skin, muscles, viscera, joints, tendons, bones) • syndromes (cancer, fibromyalgia, migraine, others) • special considerations (psychological state, age, gender, culture).
Classification of pain • Acute pain: pain of less than 3 to 6 months duration. • Chronic pain: pain lasting for more than 3-6 months, or persisting beyond the course of an acute disease, or after tissue healing is complete.
Classification of pain There are several ways to categorize pain. One is to separate it into acute pain and chronic pain. • Acute pain typically comes on suddenly and has a limited duration. It's frequently caused by damage to tissue such as bone, muscle, or organs, and the onset is often accompanied by anxiety or emotional distress. • Chronic pain lasts longer than acute pain and is generally somewhat resistant to medical treatment. This type of pain can be the result of damaged tissue, but very often is attributable to nerve damage. It's usually associated with a long-term illness.
Classification of pain Both acute and chronic pain can be debilitating, and both can affect and be affected by a person's state of mind. But the nature of chronic pain - the fact that it's ongoing and in some cases seems almost constant - makes the person who has it more susceptible to psychological consequences such as depression and anxiety. Chronic pain is further subdivided in to two classes: chronic malignant pain and chronic non-malignant pain. At the same time, psychological distress can amplify the pain.
Pain About 70% of people with chronic pain treated with pain medication experience episodes of what's called breakthrough pain. Breakthrough pain refers to flares of pain that occur even when pain medication is being used regularly. Sometimes it can be spontaneous or set off by a seemingly insignificant event such as rolling over in bed. And sometimes it may be the result of pain medication wearing off before it's time for the next dose.
Pathophysiological Classification of Pain Under this category, pain is divided into two types: • nociceptive pain • neuropathic pain. • Nociceptive Pain includes somatic and visceral pain (directly caused by the stimulation of pain nerve endings due to tissue injury or tumor infiltration). Its represents the normal response to noxious insult or injury of tissues such as skin, muscles, visceral organs, joints, tendons, or bones.
Pathophysiological Classification of Pain Somatic: musculoskeletal (joint pain, myofascial pain), cutaneous; often well localized. • Somatic pain is often described by patients as dull or aching pain. Patients are also able to point directly to the pain as the location is well defined. Pain is often worse with movement. Common causes of somatic pain include cancer metastasis to the bones or muscles due to chemotherapy drugs.
Pathophysiological Classification of Pain Visceral: hollow organs and smooth muscle; usually referred. Visceral pain is difficult to locate and the site may be actually distant from the source of the pain. It may be determined by distention of ducts leading to major organs, smooth muscle spasm, muscle ischemia, obstruction.
Pathophysiological Classification of Pain Neuropathic: pain initiated or caused by a primary lesion or disease in the somatosensory nervous system. Patients describe this type of pain as sharp, numbing, burning, or shooting in quality. This type of pain may be seen in patients: • with poorly controlled diabetes, • after viral infection (herpes zoster, chicken pox). • with cancer (metastasis to the spinal cord). • with spinal cord injury pain, phantom limb pain, and post-stroke central pain.
Pathophysiological Classification of Pain Inflammatory: a result of activation and sensitization of the nociceptive pain pathway by a variety of mediators released at a site of tissue inflammation. The mediators that have been implicated as key players are proinflammatory cytokines such IL-1-alpha, IL-1-beta, IL-6 and TNF-alpha, chemokines, reactive oxygen species, vasoactive amines, lipids, ATP, acid, and other factors released by infiltrating leukocytes, vascular endothelial cells, or tissue resident mast cells Examples include: appendicitis, rheumatoid arthritis, inflammatory bowel disease, and herpes zoster.
Pain Intensity Can be broadly categorized as: mild, moderate and severe (numeric analogue scale): • 0 = no pain • mild: <4/10 • moderate: 5/10 to 6/10 • severe: >7/10 • 10 is the worst pain imaginable.
Diagnosis of pain • Medical diagnoses related to the pain: underlying diagnoses causing pain. • Pain type (acute, neuropathic, visceral), intensity, impact on quality of life and function. • Medical comorbidities contributing to pain and/or affecting treatment: cardiovascular, cerebro-vascular or neuromuscular diseases. • Medications that may interfere with the usual choices of drug or nondrug treatments.
Diagnosis of pain Psychosocial issues and patient's ability to cope with pain. Factors that impact treatment planning and may affect response to treatment include: • depression, • anxiety, • negative emotions, • past experiences, • illness perception, • alcohol dependence, • substance abuse and • current social situations.
Treatment of pain Treatment planning establishes goals, expectations, methods and time course for treatment. The goals of pain treatment differ depending upon the type of pain and the nature of the individual case. Patient and family goals must be informated with what is possible and reasonable given the situation.
Treatment of pain Acute pain The major goals are pain control and relief while efforts are made to identify and treat the underlying disease and to enhance healing and recovery. Adequate management of acute pain may also prevent the development of chronic pain. Analgesics are the mainstay of acute pain treatment, but nondrug methods (patient education, heat/cold, massage, distraction/relaxation, others) are essential too. In some situations regional analgesia and anesthesia are also indicated.
Treatment of pain Chronic pain In most cases of chronic pain, multiple mechanisms are at play and the cause of the pain may be difficult to identify and cannot be completely eliminated. Pain relief is still primary but the goals of improvement in function and quality of life gain even greater importance. In addition to rational multidrug therapy, physical medicine and rehabilitation modalities to treat deconditioning and disability, and behavioral/psychological treatment to enhance coping and improve mood are all important. Aim for maintained or improved daily activity, family life, and return to work if possible.
