Pain
| Pain | |
|---|---|
| Specialty | Neurology, primary care, anesthesiology, emergency medicine, palliative care  |
Pain (from Ancient Greek ποινή - poine) is the unpleasant sensory and emotional experience an individual has when they perceive actual or potential tissue damage to their body.[1] Pain is highly subjective to the individual experiencing it, but medical diagnosis is based on characterising it in various ways such as the duration, severity, type (dull, burning or stabbing), and location in body. It can also be diagnosed by cause; for example, neuropathic pain is caused by damage to nerve fibres.
Pain is a major symptom in many medical conditions, significantly interfering with a person's quality of life and general functioning. In many cases, pain is self-limiting (stops without treatment) or responds to simple measures such as resting or taking a painkiller (analgesic). The study of pain has in recent years diverged into many different fields from pharmacology to psychology and neurobiology. It is also a separate sub-discipline in some terminal illnesses specializations.
Pain is part of the body's defense system, triggering a reflex reaction to retract from the painful stimuli, and helps adjust behaviour to increase avoidance of that particular harmful situation in the future.
Concept
Subjectivity
Pain is defined by medical researchers as a subjective conscious experience. The presence or absence of pain even in another human is only verifiable by their report; "Pain is whatever the experiencing person says it is, and exists whenever he says it does.[2] Currently, it is not scientifically possible to prove whether an animal is in pain or not, however it can be inferred through physical and behavioral reactions.
In veterinary science all uncertainty is overcome by assuming that if something would be painful for a human then it would be painful for an animal.[3] Where possible, analgesics are used preemptively if there is any likelihood of pain being caused to an animal.
Suffering
Suffering is usually considered a broader term than pain, and includes any unpleasant feeling or sensation. Suffering can be used in the specific sense of a painful physical sensation, but also encompasses purely emotional feelings or mental states, such as unpleasant memories. It is an individual's basic affective, or emotional, experience of unpleasantness and aversion associated with harm or threat of harm. The opinions people have about their own or someone else's suffering varies according to many factors, including its severity, the ability to avoid it, its perceived utility or related benefits, and a sense of deservedness.
All sentient beings suffer during their lives, in diverse manners, and often dramatically. No field of human activity deals with the whole subject of suffering, but many are concerned with its nature and processes, its origin and causes, its meaning and significance, its related personal, social, and cultural behaviors, its remedies, management, and uses.
The terms pain and suffering are often used in different senses which can become confusing, for example:
- being used as synonyms;
- being used in contradistinction to one another: e.g. "pain is inevitable, suffering is optional", or "pain is physical, suffering is mental";
- being used to define each other: e.g. "pain is physical suffering", or "suffering is severe physical or mental pain".
Philosophy
The concept of pain has played an important part in the study of philosophy, particularly in the philosophy of mind. The question of what pain actually consists in is still open since any evaluation is dependent upon what subject one approaches the question from. Identity theorists assert that the mental state of pain is completely identical with some physical state caused by various physiological causes. Functionalists consider pain to be defined completely by its causal role (ie in the role it has in bringing about various effects) and nothing else. Some theologians and other spiritual traditions have much to say about the nature of pain and its various spiritual consequences, especially its role in growth, understanding, compassion, and in providing an aspect of life to be overcome.
Survival benefit
Pain is an important part of the survival of humans and other animals, it encourages an organism to disengage from the noxious stimulus associated with the pain. Preliminary pain can serve to indicate that an injury is imminent, such as the ache from a soon-to-be-broken bone. Pain may also promote the healing process, since most organisms will protect an injured region in order to avoid further pain. People born with congenital insensitivity to pain usually have short life spans, and suffer numerous ailments such as broken bones, bed sores, and chronic infection.
The brain itself is devoid of nociceptive tissue, and hence cannot trigger pain. Thus, a headache is not due to stimulation of pain fibers in the brain itself. Rather, the membrane surrounding the brain and spinal cord, called the dura mater, is innervated with pain receptors, and stimulation of these dural nociceptors (pain receptors) is thought to be involved to some extent in producing headache pain, vasoconstriction of peripheral vessels being another common cause. Some evolutionary biologists have speculated that this lack of nociceptive tissue in the brain might be because any injury of sufficient magnitude to cause pain in the brain has a sufficiently high probability of being fatal that development of nociceptive tissue therein would have little to no survival benefit.
Chronic pain, in which the pain becomes pathological rather than beneficial, may be an exception to the idea that pain is helpful to survival, although some specialists believe that psychogenic chronic pain exists as a protective distraction to keep dangerous repressed emotions such as anger or rage subconscious.[4] It is not clear what the survival benefit of some extreme forms of pain (e.g. toothache) might be; and the intensity of some forms of pain (for example as a result of injury to fingernails or toenails) seem to be out of all proportion to any survival benefits.
Causes of Pain
Although rarely pain can be caused by brain damage or mental disorder, most pain is caused by our biological pain sensing system (nociception).
Nociception
This process is initiated with the stimulation of a nociceptor, due to chemical, thermal, or mechanical environment changes above it's stimulation threshold. Nociception is then carried along the nerve to the brain via the spinal cord, where it indicates possible damage of body tissues.
Nociception is the detection of a stimulus by a pain receptor (nociceptor), and transmission of the information to the brain along nerves. The anatomy of the nociceptive system can be grossly divided into the peripheral and central nervous system. The peripheral nervous system consists of small myelinated and unmyelinated nerve fibers. These nerve fibers converge into a region of the spinal cord referred to as the dorsal horn. The dorsal horn is the first relay station in pain signal transmission. The next element of pain transmission includes nerve fibers that then travel to the thalamus. From the thalamus the next order of neurons ascend to the limbic system and sensory cortex. This accounts for the affective elements and discriminative of pain respectively.[5][6]
Pain sensitivity
Genetic influences
Pain may be experienced differently depending on genotype; as an example individuals with red hair may be more susceptible to pain caused by heat[7] but redheads with a non-functional melanocortin 1 receptor (MC1R) gene are less sensitive to pain from electric shock.[8] Although the identification of human genes influencing pain has just begun, more than 230 genes are known to affect pain or analgesic sensitivity in mice.[citation needed]
Gene Nav1.7 has been identified as a major factor in the development of the pain-perception systems within the body. A rare genetic mutation in this area causes non-functional development of certain sodium channels in the nervous system, which prevents the brain from receiving messages of physical damage, resulting in congenital insensitivity to pain.[9] The same gene also appears to mediate a form of pain hyper-sensitivity, while other mutations may be the root of paroxysmal extreme pain disorder.[9] Various other sensitivities of the Somatosensory system are unaffected.[10]
Disorders
Brain damage
- Damage in the brain, in an area involved in nociception can cause central pain.
Nerve damage
Actual damage to a pain nerve, rather than it's nociceptor, due to disease or trauma can cause a false signal being sent to the thalamus, regardless of stimulus this causes the brain to perceive painful stimuli even though there is no obvious or known physiologic cause for the pain. When the trauma is caused by the loss of a limb, or from which a person no longer receives physical signals it is known as phantom pain, this is experienced by most amputees and quadriplegics. Neuropathic pain is sometime called the disease of pain and meets the criteria to be classed as pain.
Increased sensitivity
Under persistent activation nociceptive transmission to the dorsal horn may induce a wind up phenomenon. This induces pathological changes that lower the threshold for pain signals to be transmitted. In addition it may generate nonnociceptive nerve fibers to respond to pain signals. Nonnociceptive nerve fibers may also be able to generate and transmit pain signals.[11]
Insensitivity to pain
The ability to experience pain is essential for protection from injury, and recognition of the presence of injury. Insensitivity to pain is most often acquired, such as from spinal cord injury, diabetes mellitus, or more rarely Hansen's Disease[12]. Rarely, people can also suffer with congenital insensitivity to pain, or congenital analgesia. All of these individuals are at constant risk from the consequences of unrecognized injury. CIP presents in early childhood, with children frequently getting injuries such as broken bones and bruises because they fail to develop the normal avoidance of pain, thus taking risks others would not.
Misperception
Mental disorder
- Rarely a mental disorder can cause psychogenic pain, which is indistinct from the sufferer to actual physical pain.
Diagnosis
To establish an understanding of an individual's pain, health-care practitioners will typically try to establish certain characteristics of the pain, and by using the gestalt of these, the source or cause of the pain can often be established. The following characteristics are used:
Quality
The quality of the pain remains a key characteristic, and is often the first question a practitioner will ask. Typical descriptions of pain quality include sharp, stabbing, tearing, squeezing, cramping, burning, lancinating (electric-shock like), or heaviness. It may be experienced as throbbing, dull, nauseating, shooting or a combination of these. Indeed, individuals who are clearly in extreme distress such as from a myocardial infarction may not describe the sensation as pain, but instead as an extreme heaviness on the chest. Another individual with pain in the same region and with the same intensity may describe the pain as tearing which would lead the practitioner to consider aortic dissection. Inflammatory pain is commonly associated with some degree of itch sensation, leading to a chronic urge to rub or otherwise stimulate the affected area. The difference between these diagnoses and many others rests on the quality of the pain.
Intensity
Pain may range in intensity from slight through severe to agonizing and can appear as constant or intermittent. The threshold of pain varies widely between individuals. Many attempts have been made to create a Pain scale that can be used to quantify pain. The purpose of these scales is to monitor an individual's pain over time, allowing care-givers to monitor response to therapy for example. Accurate quantification can also allow researchers to compare results between groups of patients. Pain may be quantified on a pain numeric rating scale (NRS) that ranges from 1-10 points; the accuracy of such as scale (using a cut point of 4 or more) for predicting pain that interferes with functioning is:[13]
- sensitivity 64%
- specificity 83%
Localization
Localization is the term used to decribe the subjective experience of pain being in a specific area or region of the body. Localization is not always accurate in defining the problematic area, although the region will often help narrow the diagnostic possibilities. Some pain sensations may be diffuse or referred. Referred pain usually happens when sensory fibres from the viscera enter the same segment of the spinal cord as somatic nerves i.e. those from superficial tissues. The sensory nerve from the viscera stimulates the nearby somatic nerve so that the pain localization in the brain is confused. A well-known example is when heart damage is perceived as pain the left shoulder or arm.[14] Localization results in specific pain being named as as neck pain, cutaneous pain, kidney pain, or the painful uterine contractions occurring during childbirth etc. This common usage is not consistent with the scientists' model of pain being a subjective experience. The types of pain that can be classified by localisation are:
Cutaneous pain
Caused by injury to the skin or superficial tissues. Cutaneous nociceptors terminate just below the skin, and due to the high concentration of nerve endings, produce a well-defined, localized pain of short duration. Examples of injuries that produce cutaneous pain include paper cuts, minor cuts, minor (first degree) burns and lacerations.
Somatic pain
Originates from the neuromusculoskeletal system including muscles, ligaments, tendons, bones, blood vessels, and even nerves themselves. It is detected with somatic nociceptors. The scarcity of pain receptors in these areas produces a dull, poorly-localized pain of longer duration than cutaneous pain; examples include sprains and broken bones. Myofascial pain usually is caused by trigger points in muscles, tendons and fascia, and may be local or referred.
Visceral pain
Originates from body's viscera, or organs. Visceral nociceptors are located within body organs and internal cavities. The even greater scarcity of nociceptors in these areas produces pain that is usually more aching and of a longer duration than somatic pain. Visceral pain is extremely difficult to localize, and several injuries to visceral tissue exhibit "referred" pain, where the sensation is localized to an area completely unrelated to the site of injury. Myocardial ischaemia (the loss of blood flow to a part of the heart muscle tissue) is possibly the best known example of referred pain; the sensation can occur in the upper chest as a restricted feeling, or as an ache in the left shoulder, arm or even hand. The popularized term "brain freeze" is another example of referred pain, in which the vagus nerve is cooled by cold inside the throat. Referred pain can be explained by the findings that pain receptors in the viscera also excite spinal cord neurons that are excited by cutaneous tissue. Since the brain normally associates firing of these spinal cord neurons with stimulation of somatic tissues in skin or muscle, pain signals arising from the viscera are interpreted by the brain as originating from the skin. The theory that visceral and somatic pain receptors converge and form synapses on the same spinal cord pain-transmitting neurons is called "Ruch's Hypothesis".
Referred pain
Visceral pain sensation is often referred by the CNS to a dermatome, sclerotome or myotome region which may be far away from the originating source. This is explained, in part, due to a common embryological origin known as a somite in developing embryo. Examples of this include the heart which originates in the neck, thus producing the classical pain and arm pain experienced during acute cardiac pain.
Radiation
Radiation of pain occurs when stimulus of a nerve at one site is perceived as pain in the sensory distribution of that nerve. Sciatica is the symptom of pain running down the back of the buttock, leg and bottom of foot that results from compression of a nerve root in the lumbar spine.
Frequency and duration
Onset and offset
Exacerbating factors
Ameliorating factors
Treatment and management
Pain Management divides symptoms into acute or chronic. The distinction between these definitions is based on the nature of the pain rather than the duration of sensation.
Acute pain
General physicians are experienced with treating acute pain, which usually is caused by soft tissue damage, infection and/or inflammation among other causes. It is usually treated simultaneously with pharmaceuticals or appropriate techniques for removing the cause and pharmaceuticals or appropriate techniques for controlling the pain sensation, commonly analgesics. Acute pain serves to alert after an injury or malfunction of the body. Failure to treat acute pain properly may lead to chronic pain.[15]
Chronic pain
Specialists are usually needed for chronic pain management.
Chronic pain may have no apparent cause or may be caused by a developing illness or imbalance. This disorder can trigger multiple psychological problems that are confounding, leading to various differential diagnoses. Sometimes chronic pain can have a psychosomatic or psychogenic cause.[4] Chronic pain is sometimes referred to as the "disease of pain"
Other
Hypnosis as well as diverse perceptional techniques provoking altered states of consciousness have proven to be of important help in the management of all types of pain.[16] Some kinds of physical manipulation or exercise are showing interesting results as well.[17]
Alternative medicine
A survey of American adults found pain was the most common reason that people use alternative medicine. Among American adults who used complementary and alternative medicine (CAM) in 2002, 16.8% used CAM to treat back pain; 6.6% for neck pain; 4.9% for arthritis; 4.9% for joint pain; 3.1% for headache; and 2.4% used CAM to treat recurring pain, with some using CAM to treat more than one condition.[18]
Traditional Chinese medicine views pain as a 'blocked' qi, akin to electrical resistance, with treatments such as acupuncture claimed as more effective for nontraumatic pain than traumatic pain. Although the mechanism is not fully understood, acupuncture may stimulate the release of large quantities of endogenous opioids.[19] A 2004 NCCAM-funded study showed that acupuncture provides pain relief and improved function in patients with osteoarthritis of the knee, causing some managed care organizations to support acupuncture as adjunctive therapy for this purpose.[20] The National Institutes of Health's 1997 Consensus Statement on Acupunture notes that research has been mixed, partly due to difficulties with designing clinical studies with the proper controls.[21]
CAM may also involve the use of nutritional supplements in pain treatment. Options include curcumin, a polyphenol found in turmeric and a natural COX-2 inhibitor,[22] glucosamine, chondroitin, bromelain and omega-3 fatty acids. Glucosamine and chondroitin were found to be effective only in a minority of pain patients, those suffering from moderate to severe pain, but was otherwise equivalent to a placebo.[23]
See also
References
- ^ IASP Pain Terminology International Association for the Study of Pain definition of pain
- ^ cite sourced from McCaffery M. Nursing management of the patient in pain. Philadelphia, Pa: JB Lippincott 1972.
- ^ American College of Veterinary Anesthesiologists' position paper on the treatment of pain in animals retrieved 2007-01-06
- ^ a b Sarno, John E., MD, et al., The Divided Mind: The Epidemic of Mindbody Disorders 2006 (ISBN 0-06-085178-3)
- ^ Romanelli P, Esposito V (2004). "The functional anatomy of neuropathic pain". Neurosurg. Clin. N. Am. 15 (3): 257–68. PMID 15246335.
- ^ Vanderah TW (2007). "Pathophysiology of pain". Med. Clin. North Am. 91 (1): 1–12. PMID 17164100.
- ^ Liem EB, Joiner TV, Tsueda K, Sessler DI (2005). "Increased sensitivity to thermal pain and reduced subcutaneous lidocaine efficacy in redheads". Anesthesiology. 102 (3): 509–14. PMID 15731586.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Mogil JS, Ritchie J, Smith SB; et al. (2005). "Melanocortin-1 receptor gene variants affect pain and mu-opioid analgesia in mice and humans". J. Med. Genet. 42 (7): 583–7. doi:10.1136/jmg.2004.027698. PMID 15994880.
{{cite journal}}: Explicit use of et al. in:|author=(help)CS1 maint: multiple names: authors list (link) - ^ a b Fertleman CR, Baker MD, Parker KA; et al. (2006). "SCN9A mutations in paroxysmal extreme pain disorder: allelic variants underlie distinct channel defects and phenotypes". Neuron. 52 (5): 767–74. doi:10.1016/j.neuron.2006.10.006. PMID 17145499.
{{cite journal}}: Explicit use of et al. in:|author=(help)CS1 maint: multiple names: authors list (link) - ^ Hopkin, M (2006-12-13). "The mutation that takes away pain". Nature News. doi:10.1038/news061211-11. Retrieved 2008-03-29.
- ^ Vadivelu N, Sinatra R (2005). "Recent advances in elucidating pain mechanisms". Current opinion in anaesthesiology. 18 (5): 540–7. PMID 16534290.
- ^ Brand, Paul (c1997). The gift of pain : why we hurt & what we can do about it. Zondervan Publ. ISBN 0-310-22144-7.
{{cite book}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Krebs, Carey, and Weinberger, “Accuracy of the Pain Numeric Rating Scale as a Screening Test in Primary Care,” Journal of General Internal Medicine 22, no. 10 (October 21, 2007): 1453-1458, doi:10.1007/s11606-007-0321-2 (accessed September 28, 2007).
- ^ Ann Waugh, Allison Grant (001). Anatomy and Physiology in Health and Illness. Edinburgh: Churchill Livingstone. pp. pp 174-175. ISBN 0443-06468 7.
{{cite book}}:|pages=has extra text (help); Check date values in:|date=(help) - ^ Dahl JB, Moiniche S (2004). "Pre-emptive analgesia". Br Med Bull. 71: 13–27. PMID 15596866.
- ^ Robert Ornstein PhD, David Sobel MD (1988). The Healing Brain. New York: Simon & Schuster Inc. pp. pp 98-99. ISBN -671-66236-8.
{{cite book}}:|pages=has extra text (help); Check|isbn=value: length (help) - ^ Douglas E DeGood, Donald C Manning MD, Susan J Middaugh (1997). The headache & Neck Pain Workbook. Oakland, California: New Harbinger Publications. ISBN 1-57224-086-5.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ Barnes, P (2004-05-27), CDC Advance Data Report #343. Complementary and Alternative Medicine Use Among Adults: United States, 2002, U.S. National Center for Complementary and Alternative Medicine
{{citation}}: Unknown parameter|coauthors=ignored (|author=suggested) (help); news release. - ^ Sapolsky, Robert M. (1998). Why zebras don't get ulcers: An updated guide to stress, stress-related diseases, and coping. New York: W.H. Freeman and CO. ISBN 0-585-36037-5.
- ^ Berman BM, Lao L, Langenberg P, Lee WL, Gilpin AM, Hochberg MC (2004). "Effectiveness of acupuncture as adjunctive therapy in osteoarthritis of the knee: a randomized, controlled trial". Ann. Intern. Med. 141 (12): 901–10. PMID 15611487.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Ramsay (1997-11-5). "The National Institutes of Health (NIH) Consensus Development Program: Acupuncture". Retrieved 2008-03-29.
{{cite web}}: Check date values in:|date=(help); Text "first DJ" ignored (help) - ^ Sharma S, Kulkarni SK, Agrewala JN, Chopra K (2006). "Curcumin attenuates thermal hyperalgesia in a diabetic mouse model of neuropathic pain". Eur. J. Pharmacol. 536 (3): 256–61. doi:10.1016/j.ejphar.2006.03.006. PMID 16584726.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Clegg DO, Reda DJ, Harris CL; et al. (2006). "Glucosamine, chondroitin sulfate, and the two in combination for painful knee osteoarthritis". N. Engl. J. Med. 354 (8): 795–808. doi:10.1056/NEJMoa052771. PMID 16495392.
{{cite journal}}: Explicit use of et al. in:|author=(help)CS1 maint: multiple names: authors list (link)
External links
- Template:DMOZ
- Acute Pain Medicine: Scientific Evidence (2nd ed) (2007 updated version)
- relief of pain and suffering: exhibit prepared with Symposium: "Pain and Suffering in History–Narratives of Science, Medicine and Culture,"