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| {{Infobox_Disease |
| | __NOTOC__ |
| Name = Pain |
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| ICD10 = R52 |
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| ICD9 = {{ICD9|338}}|
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| ICDO = |
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| Image = |
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| Caption = |
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| OMIM = |
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| MedlinePlus = 002164|
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| eMedicineSubj = |
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| eMedicineTopic = |
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| DiseasesDB = 9503 |
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| MeshID = D010146 |
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| }}
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| {{Pain symptom}} | | {{Pain symptom}} |
| {{CMG}} | | {{CMG}}; '''Associate Editor(s)-in-Chief:''' [[User:Aditya Govindavarjhulla|Aditya Govindavarjhulla, M.B.B.S.]] [mailto:agovi@wikidoc.org], [[User:Raviteja Reddy Guddeti|Raviteja Guddeti, M.B.B.S.]] [mailto:ravitheja.g@gmail.com] |
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| ==[[Pain overview|Overview]]== | | ==[[Pain overview|Overview]]== |
| ==[[Pain historical perspective|History of Pain]]==
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| ==[[Pain pathophysiology|Mechanism]]==
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| ==[[Pain epidemiology and demographic|Epidemiology and Demographics]]==
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| ==[[Pain diagnosis|Diagnosis]]==
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| ==[[Pain treatment|Management]]==
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| ==Overview of the Nervous Systems==
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| The central nervous system (CNS) refers to the brain and spinal cord together. The peripheral nervous system refers to the cervical, thoracic, lumbar, and sacral nerve trunks leading away from the spine to the limbs. Messages related to function (such as movement) or dysfunction (such as pain) travel from the brain to the spinal cord and from there to other regions in the body and back to the brain again. The autonomic nervous system controls involuntary functions in the body, like perspiration, blood pressure, heart rate, or heart beat. It is divided into the sympathetic and parasympathetic nervous systems. The sympathetic and parasympathetic nervous systems have links to important organs and systems in the body; for example, the sympathetic nervous system controls the heart, blood vessels, and respiratory system, while the parasympathetic nervous system controls our ability to sleep, eat, and digest food.
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| The peripheral nervous system also includes 12 pairs of cranial nerves located on the underside of the brain. Most relay messages of a sensory nature. They include the olfactory (I), optic (II), oculomotor (III), trochlear (IV), trigeminal (V), abducens (VI), facial (VII), vestibulocochlear (VIII), glossopharyngeal (IX), vagus (X), accessory (XI), and hypoglossal (XII) nerves. Neuralgia, as in trigeminal neuralgia, is a term that refers to pain that arises from abnormal activity of a nerve trunk or its branches. The type and severity of pain associated with neuralgia vary widely.
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| ==A Pain Primer: What Do We Know About Pain?==
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| We may experience pain as a prick, tingle, sting, burn, or ache. Receptors on the skin trigger a series of events, beginning with an electrical impulse that travels from the skin to the spinal cord. The spinal cord acts as a sort of relay center where the pain signal can be blocked, enhanced, or otherwise modified before it is relayed to the brain. One area of the spinal cord in particular, called the dorsal horn (see section on Spine Basics in the Appendix), is important in the reception of pain signals.
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| The most common destination in the brain for pain signals is the thalamus and from there to the cortex, the headquarters for complex thoughts. The thalamus also serves as the brain's storage area for images of the body and plays a key role in relaying messages between the brain and various parts of the body. In people who undergo an amputation, the representation of the amputated limb is stored in the thalamus. (For a discussion of the thalamus and its role in this phenomenon, called phantom pain, see section on Phantom Pain)
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| Pain is a complicated process that involves an intricate interplay between a number of important chemicals found naturally in the brain and spinal cord. In general, these chemicals, called neurotransmitters, transmit nerve impulses from one cell to another.
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| There are many different neurotransmitters in the human body; some play a role in human disease and, in the case of pain, act in various combinations to produce painful sensations in the body. Some chemicals govern mild pain sensations; others control intense or severe pain.
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| The body's chemicals act in the transmission of pain messages by stimulating neurotransmitter receptors found on the surface of cells; each receptor has a corresponding neurotransmitter. Receptors function much like gates or ports and enable pain messages to pass through and on to neighboring cells. One brain chemical of special interest to neuroscientists is glutamate. During experiments, mice with blocked glutamate receptors show a reduction in their responses to pain. Other important receptors in pain transmission are opiate-like receptors. Morphine and other opioid drugs work by locking on to these opioid receptors, switching on pain-inhibiting pathways or circuits, and thereby blocking pain.
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| Another type of receptor that responds to painful stimuli is called a nociceptor. Nociceptors are thin nerve fibers in the skin, muscle, and other body tissues, that, when stimulated, carry pain signals to the spinal cord and brain. Normally, nociceptors only respond to strong stimuli such as a pinch. However, when tissues become injured or inflamed, as with a sunburn or infection, they release chemicals that make nociceptors much more sensitive and cause them to transmit pain signals in response to even gentle stimuli such as breeze or a caress. This condition is called allodynia -a state in which pain is produced by innocuous stimuli.
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| The body's natural painkillers may yet prove to be the most promising pain relievers, pointing to one of the most important new avenues in drug development. The brain may signal the release of painkillers found in the spinal cord, including serotonin, norepinephrine, and opioid-like chemicals. Many pharmaceutical companies are working to synthesize these substances in laboratories as future medications.
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| Endorphins and enkephalins are other natural painkillers. Endorphins may be responsible for the "feel good" effects experienced by many people after rigorous exercise; they are also implicated in the pleasurable effects of smoking.
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| Similarly, peptides, compounds that make up proteins in the body, play a role in pain responses. Mice bred experimentally to lack a gene for two peptides called tachykinins-neurokinin A and substance P-have a reduced response to severe pain. When exposed to mild pain, these mice react in the same way as mice that carry the missing gene. But when exposed to more severe pain, the mice exhibit a reduced pain response. This suggests that the two peptides are involved in the production of pain sensations, especially moderate-to-severe pain. Continued research on tachykinins, conducted with support from the NINDS, may pave the way for drugs tailored to treat different severities of pain.
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| Scientists are working to develop potent pain-killing drugs that act on receptors for the chemical acetylcholine. For example, a type of frog native to Ecuador has been found to have a chemical in its skin called epibatidine, derived from the frog's scientific name, Epipedobates tricolor. Although highly toxic, epibatidine is a potent analgesic and, surprisingly, resembles the chemical nicotine found in cigarettes. Also under development are other less toxic compounds that act on acetylcholine receptors and may prove to be more potent than morphine but without its addictive properties.
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| The idea of using receptors as gateways for pain drugs is a novel idea, supported by experiments involving substance P. Investigators have been able to isolate a tiny population of neurons, located in the spinal cord, that together form a major portion of the pathway responsible for carrying persistent pain signals to the brain. When animals were given injections of a lethal cocktail containing substance P linked to the chemical saporin, this group of cells, whose sole function is to communicate pain, were killed. Receptors for substance P served as a portal or point of entry for the compound. Within days of the injections, the targeted neurons, located in the outer layer of the spinal cord along its entire length, absorbed the compound and were neutralized. The animals' behavior was completely normal; they no longer exhibited signs of pain following injury or had an exaggerated pain response. Importantly, the animals still responded to acute, that is, normal, pain. This is a critical finding as it is important to retain the body's ability to detect potentially injurious stimuli. The protective, early warning signal that pain provides is essential for normal functioning. If this work can be translated clinically, humans might be able to benefit from similar compounds introduced, for example, through lumbar (spinal) puncture.
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| Another promising area of research using the body's natural pain-killing abilities is the transplantation of chromaffin cells into the spinal cords of animals bred experimentally to develop arthritis. Chromaffin cells produce several of the body's pain-killing substances and are part of the adrenal medulla, which sits on top of the kidney. Within a week or so, rats receiving these transplants cease to exhibit telltale signs of pain. Scientists, working with support from the NINDS, believe the transplants help the animals recover from pain-related cellular damage. Extensive animal studies will be required to learn if this technique might be of value to humans with severe pain.
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| One way to control pain outside of the brain, that is, peripherally, is by inhibiting hormones called prostaglandins. Prostaglandins stimulate nerves at the site of injury and cause inflammation and fever. Certain drugs, including NSAIDs, act against such hormones by blocking the enzyme that is required for their synthesis.
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| Blood vessel walls stretch or dilate during a migraine attack and it is thought that serotonin plays a complicated role in this process. For example, before a migraine headache, serotonin levels fall. Drugs for migraine include the triptans: sumatriptan (Imitrix®), naratriptan (Amerge®), and zolmitriptan (Zomig®). They are called serotonin agonists because they mimic the action of endogenous (natural) serotonin and bind to specific subtypes of serotonin receptors.
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| Ongoing pain research, much of it supported by the NINDS, continues to reveal at an unprecedented pace fascinating insights into how genetics, the immune system, and the skin contribute to pain responses.
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| The explosion of knowledge about human genetics is helping scientists who work in the field of drug development. We know, for example, that the pain-killing properties of codeine rely heavily on a liver enzyme, CYP2D6, which helps convert codeine into morphine. A small number of people genetically lack the enzyme CYP2D6; when given codeine, these individuals do not get pain relief. CYP2D6 also helps break down certain other drugs. People who genetically lack CYP2D6 may not be able to cleanse their systems of these drugs and may be vulnerable to drug toxicity. CYP2D6 is currently under investigation for its role in pain.
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| In his research, the late John C. Liebeskind, a renowned pain expert and a professor of psychology at UCLA, found that pain can kill by delaying healing and causing cancer to spread. In his pioneering research on the immune system and pain, Dr. Liebeskind studied the effects of stress-such as surgery-on the immune system and in particular on cells called natural killer or NK cells. These cells are thought to help protect the body against tumors. In one study conducted with rats, Dr. Liebeskind found that, following experimental surgery, NK cell activity was suppressed, causing the cancer to spread more rapidly. When the animals were treated with morphine, however, they were able to avoid this reaction to stress.
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| The link between the nervous and immune systems is an important one. Cytokines, a type of protein found in the nervous system, are also part of the body's immune system, the body's shield for fighting off disease. Cytokines can trigger pain by promoting inflammation, even in the absence of injury or damage. Certain types of cytokines have been linked to nervous system injury. After trauma, cytokine levels rise in the brain and spinal cord and at the site in the peripheral nervous system where the injury occurred. Improvements in our understanding of the precise role of cytokines in producing pain, especially pain resulting from injury, may lead to new classes of drugs that can block the action of these substances.
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| ==The Two Faces of Pain: Acute and Chronic==
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| What is pain? The International Association for the Study of Pain defines it as: An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.
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| It is useful to distinguish between two basic types of pain, acute and chronic, and they differ greatly.
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| * Acute pain, for the most part, results from disease, inflammation, or injury to tissues. This type of pain generally comes on suddenly, for example, after trauma or surgery, and may be accompanied by anxiety or emotional distress. The cause of acute pain can usually be diagnosed and treated, and the pain is self-limiting, that is, it is confined to a given period of time and severity. In some rare instances, it can become chronic.
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| * Chronic pain is widely believed to represent disease itself. It can be made much worse by environmental and psychological factors. Chronic pain persists over a longer period of time than acute pain and is resistant to most medical treatments. It can—and often does—cause severe problems for patients.
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| ==Clarification on the use of certain pain-related terms==
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| The word ''pain'' used without a modifier usually refers to physical pain, but it may also refer to pain in the broad sense, i.e. [[suffering]]. The latter includes physical pain and mental pain, or any unpleasant feeling, sensation, and emotion. It may be described as a private feeling of unpleasantness and aversion associated with harm or threat of harm in an individual. Care should be taken to make the appropriate distinction when required between the two meanings. For instance, [[Pain (philosophy)|philosophy of pain]] is essentially about physical pain, while a philosophical outlook on pain is rather about pain in the broad sense. Or, as another quite different instance, [[nausea]] or [[itch]] are not 'physical pains', but they are unpleasant sensory or bodily experience, and a person 'suffering' from severe or prolonged nausea or itch may be said 'in pain'.
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| [[Nociception]], the unconscious activity induced by a harmful stimulus in sense receptors, peripheral nerves, spinal column and brain, should not be confused with physical pain, which is a conscious experience. Nociception or noxious stimuli usually cause pain, but not always, and sometimes pain occurs without them.<ref name="nociIASP">"Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause." Source: [http://www.iasp-pain.org/AM/Template.cfm?Section=General_Resource_Links&Template=/CM/HTMLDisplay.cfm&ContentID=3058 IASP Pain Terminology].</ref>
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| Qualifiers, such as ''mental'', ''emotional'', ''psychological'', and ''spiritual'', are often used for referring to more specific types of pain or suffering. In particular, 'mental pain' may be used in relationship with 'physical pain' for distinguishing between two wide categories of pain. A first caveat concerning such a distinction is that it uses 'physical pain' in a sense that normally includes not only the 'typical sensory experience' of 'physical pain' but also other unpleasant bodily experience such as itch or nausea. A second caveat is that the terms ''physical'' or ''mental'' should not be taken too literally: physical pain, as a matter of fact, happens through conscious minds and involves emotional aspects, while mental pain happens through physical brains and, being an emotion, it involves important bodily physiological aspects.
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| The term ''unpleasant'' or ''unpleasantness'' commonly means painful or painfulness in a broad sense. It is also used in (physical) pain science for referring to the affective dimension of pain, usually in contrast with the sensory dimension. For instance: “Pain-unpleasantness is often, though not always, closely linked to both the intensity and unique qualities of the painful sensation.”<ref>Donald D. Price, [http://molinterv.aspetjournals.org/cgi/content/full/2/6/392 Central Neural Mechanisms that Interrelate Sensory and Affective Dimensions of Pain], ‘’Molecular Interventions’’ 2:392-403 (2002)</ref> Pain science acknowledges, in a puzzling challenge to IASP definition, that pain may be experienced as a sensation devoid of any unpleasantness: see below [[#Pain asymbolia|pain asymbolia]].<ref name="asymbolia"/>
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| [[Suffering]] is sometimes used in the specific narrow sense of physical pain, but more often it refers to mental pain, or more often yet to pain in the broad sense. Suffering is described as an individual's basic [[affective]] experience of unpleasantness and aversion associated with harm or threat of harm.
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| The terms ''pain'' and ''suffering'' are often used together in different senses which can become confusing, for example:
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| *being used as synonyms;
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| *being used in ''contradistinction'' to one another: e.g. "pain is inevitable, suffering is optional", or "pain is physical, suffering is mental";
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| *being used to define each other: e.g. "pain is physical suffering", or "suffering is severe physical or mental pain".
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| To avoid confusion: this article is about physical pain in the narrow sense of a typical sensory experience associated with actual or potential tissue damage. This excludes pain in the broad sense of any unpleasant experience, which is covered in detail by the article [[Suffering]].
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| ==The A to Z of Pain==
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| Hundreds of pain syndromes or disorders make up the spectrum of pain. There are the most benign, fleeting sensations of pain, such as a pin prick. There is the pain of childbirth, the pain of a heart attack, and the pain that sometimes follows amputation of a limb. There is also pain accompanying cancer and the pain that follows severe trauma, such as that associated with head and spinal cord injuries. A sampling of common pain syndromes follows, listed alphabetically.
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| '''Arachnoiditis''' is a condition in which one of the three membranes covering the brain and spinal cord, called the arachnoid membrane, becomes inflamed. A number of causes, including infection or trauma, can result in inflammation of this membrane. Arachnoiditis can produce disabling, progressive, and even permanent pain.
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| '''Arthritis'''. Millions of Americans suffer from arthritic conditions such as osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, and gout. These disorders are characterized by joint pain in the extremities. Many other inflammatory diseases affect the body's soft tissues, including tendonitis and bursitis.
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| '''Back pain''' has become the high price paid by our modern lifestyle and is a startlingly common cause of disability for many Americans, including both active and inactive people. Back pain that spreads to the leg is called sciatica and is a very common condition (see below). Another common type of back pain is associated with the discs of the spine, the soft, spongy padding between the vertebrae (bones) that form the spine. Discs protect the spine by absorbing shock, but they tend to degenerate over time and may sometimes rupture. Spondylolisthesis is a back condition that occurs when one vertebra extends over another, causing pressure on nerves and therefore pain. Also, damage to nerve roots (see Spine Basics in the Appendix) is a serious condition, called radiculopathy, that can be extremely painful. Treatment for a damaged disc includes drugs such as painkillers, muscle relaxants, and steroids; exercise or rest, depending on the patient's condition; adequate support, such as a brace or better mattress and physical therapy. In some cases, surgery may be required to remove the damaged portion of the disc and return it to its previous condition, especially when it is pressing a nerve root. Surgical procedures include discectomy, laminectomy, or spinal fusion (see section on surgery in How is Pain Treated? for more information on these treatments).
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| '''Burn pain''' can be profound and poses an extreme challenge to the medical community. First-degree burns are the least severe; with third-degree burns, the skin is lost. Depending on the injury, pain accompanying burns can be excruciating, and even after the wound has healed patients may have chronic pain at the burn site.
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| '''Central pain syndrome'''-see "Trauma" below.
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| '''Cancer pain''' can accompany the growth of a tumor, the treatment of cancer, or chronic problems related to cancer's permanent effects on the body. Fortunately, most cancer pain can be treated to help minimize discomfort and stress to the patient.
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| '''Headaches''' affect millions of Americans. The three most common types of chronic headache are migraines, cluster headaches, and tension headaches. Each comes with its own telltale brand of pain.
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| * '''Migraines''' are characterized by throbbing pain and sometimes by other symptoms, such as nausea and visual disturbances. Migraines are more frequent in women than men. Stress can trigger a migraine headache, and migraines can also put the sufferer at risk for stroke.
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| * '''Cluster headaches''' are characterized by excruciating, piercing pain on one side of the head; they occur more frequently in men than women.
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| * '''Tension headaches''' are often described as a tight band around the head.
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| '''Head and facial pain''' can be agonizing, whether it results from dental problems or from disorders such as cranial neuralgia, in which one of the nerves in the face, head, or neck is inflamed. Another condition, trigeminal neuralgia (also called tic douloureux), affects the largest of the cranial nerves and is characterized by a stabbing, shooting pain.
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| '''Muscle pain''' can range from an aching muscle, spasm, or strain, to the severe spasticity that accompanies paralysis. Another disabling syndrome is fibromyalgia, a disorder characterized by fatigue, stiffness, joint tenderness, and widespread muscle pain. Polymyositis, dermatomyositis, and inclusion body myositis are painful disorders characterized by muscle inflammation. They may be caused by infection or autoimmune dysfunction and are sometimes associated with connective tissue disorders, such as lupus and rheumatoid arthritis.
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| '''Myofascial pain syndromes''' affect sensitive areas known as trigger points, located within the body's muscles. Myofascial pain syndromes are sometimes misdiagnosed and can be debilitating. Fibromyalgia is a type of myofascial pain syndrome.
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| '''Neuropathic pain''' is a type of pain that can result from injury to nerves, either in the peripheral or central nervous system (see The Nervous Systems in the Appendix). Neuropathic pain can occur in any part of the body and is frequently described as a hot, burning sensation, which can be devastating to the affected individual. It can result from diseases that affect nerves (such as diabetes) or from trauma, or, because chemotherapy drugs can affect nerves, it can be a consequence of cancer treatment. Among the many neuropathic pain conditions are diabetic neuropathy (which results from nerve damage secondary to vascular problems that occur with diabetes); reflex sympathetic dystrophy syndrome (see below), which can follow injury; phantom limb and post-amputation pain (see Phantom Pain in the Appendix), which can result from the surgical removal of a limb; postherpetic neuralgia, which can occur after an outbreak of shingles; and central pain syndrome, which can result from trauma to the brain or spinal cord.
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| '''Reflex sympathetic dystrophy syndrome''', or RSDS, is accompanied by burning pain and hypersensitivity to temperature. Often triggered by trauma or nerve damage, RSDS causes the skin of the affected area to become characteristically shiny. In recent years, RSDS has come to be called complex regional pain syndrome (CRPS); in the past it was often called causalgia.
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| '''Repetitive stress injuries''' are muscular conditions that result from repeated motions performed in the course of normal work or other daily activities. They include:
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| * writer's cramp, which affects musicians and writers and others,
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| * compression or entrapment neuropathies, including carpal tunnel syndrome, caused by chronic overextension of the wrist and
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| * tendonitis or tenosynovitis, affecting one or more tendons.
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| '''Sciatica''' is a painful condition caused by pressure on the sciatic nerve, the main nerve that branches off the spinal cord and continues down into the thighs, legs, ankles, and feet. Sciatica is characterized by pain in the buttocks and can be caused by a number of factors. Exertion, obesity, and poor posture can all cause pressure on the sciatic nerve. One common cause of sciatica is a herniated disc (see Spine Basics in the Appendix).
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| '''Shingles''' and other painful disorders affect the skin. Pain is a common symptom of many skin disorders, even the most common rashes. One of the most vexing neurological disorders is shingles or herpes zoster, an infection that often causes agonizing pain resistant to treatment. Prompt treatment with antiviral agents is important to arrest the infection, which if prolonged can result in an associated condition known as postherpetic neuralgia. Other painful disorders affecting the skin include:
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| * vasculitis, or inflammation of blood vessels;
| | ==[[Pain historical perspective|Historical Perspective]]== |
| * other infections, including herpes simplex;
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| * skin tumors and cysts, and
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| * tumors associated with neurofibromatosis, a neurogenetic disorder.
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| '''Sports injuries''' are common. Sprains, strains, bruises, dislocations, and fractures are all well-known words in the language of sports. Pain is another. In extreme cases, sports injuries can take the form of costly and painful spinal cord and head injuries, which cause severe suffering and disability.
| | ==[[Pain anatomy|Anatomy]]== |
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| Spinal stenosis refers to a narrowing of the canal surrounding the spinal cord. The condition occurs naturally with aging. Spinal stenosis causes weakness in the legs and leg pain usually felt while the person is standing up and often relieved by sitting down.
| | ==[[Pain classification|Classification]]== |
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| '''Surgical pain''' may require regional or general anesthesia during the procedure and medications to control discomfort following the operation. Control of pain associated with surgery includes presurgical preparation and careful monitoring of the patient during and after the procedure.
| | ==[[Pain pathophysiology|Pathophysiology]]== |
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| '''Temporomandibular disorders''' are conditions in which the temporomandibular joint (the jaw) is damaged and/or the muscles used for chewing and talking become stressed, causing pain. The condition may be the result of a number of factors, such as an injury to the jaw or joint misalignment, and may give rise to a variety of symptoms, most commonly pain in the jaw, face, and/or neck muscles. Physicians reach a diagnosis by listening to the patient's description of the symptoms and by performing a simple examination of the facial muscles and the temporomandibular joint.
| | ==[[Pain causes|Causes]]== |
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| '''Trauma''' can occur after injuries in the home, at the workplace, during sports activities, or on the road. Any of these injuries can result in severe disability and pain. Some patients who have had an injury to the spinal cord experience intense pain ranging from tingling to burning and, commonly, both. Such patients are sensitive to hot and cold temperatures and touch. For these individuals, a touch can be perceived as intense burning, indicating abnormal signals relayed to and from the brain. This condition is called central pain syndrome or, if the damage is in the thalamus (the brain's center for processing bodily sensations), thalamic pain syndrome. It affects as many as 100,000 Americans with multiple sclerosis, Parkinson's disease, amputated limbs, spinal cord injuries, and stroke. Their pain is severe and is extremely difficult to treat effectively. A variety of medications, including analgesics, antidepressants, anticonvulsants, and electrical stimulation, are options available to central pain patients.
| | ==[[Pain differential diagnosis|Differentiating Pain from other Diseases]]== |
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| '''Vascular disease''' or injury-such as vasculitis or inflammation of blood vessels, coronary artery disease, and circulatory problems-all have the potential to cause pain. Vascular pain affects millions of Americans and occurs when communication between blood vessels and nerves is interrupted. Ruptures, spasms, constriction, or obstruction of blood vessels, as well as a condition called ischemia in which blood supply to organs, tissues, or limbs is cut off, can also result in pain.
| | ==[[Pain epidemiology and demographics|Epidemiology and Demographics]]== |
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| | ==[[Pain risk factors|Risk Factors]]== |
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| | ==[[Pain natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
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| ==Special cases== | | ==Diagnosis== |
| ===Phantom pain===
| | [[Pain history and symptoms|History and Symptoms]] | [[Pain physical examination|Physical Examination]] | [[Pain laboratory findings|Laboratory Findings]] | [[Pain electrocardiogram|Electrocardiogram]] | [[Pain x ray|X Ray]] | [[Pain CT|CT]] | [[Pain MRI|MRI]] | [[Pain echocardiography or ultrasound|Echocardiography or Ultrasound]] | [[Pain other imaging findings|Other Imaging Findings]] |[[Pain other diagnostic studies|Other Diagnostic Studies]] |
| {{main|Phantom pain}}
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| [[Phantom pain]] is the sensation of pain from a limb or organ that has been lost or from which a person no longer receives physical signals. [[Phantom limb pain]] is an experience almost universally reported by [[amputee]]s and [[quadriplegia|quadriplegic]]s. Phantom pain is a neuropathic pain. | | ==Treatment== |
| | [[Pain medical therapy|Medical Therapy]] | [[Pain psychotherapy|Psychotherapy]] |[[Pain surgery|Surgery]] | [[Pain primary prevention|Primary Prevention]] | [[Pain secondary prevention|Secondary Prevention]] | [[Pain cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Pain future or investigational therapies|Future or Investigational Therapies]] |
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| Sometimes, when a limb is removed during an amputation, an individual will continue to have an internal sense of the lost limb. This phenomenon is known as phantom limb and accounts describing it date back to the 1800s. Similarly, many amputees are frequently aware of severe pain in the absent limb. Their pain is real and is often accompanied by other health problems, such as depression.
| | == Case Studies == |
| | [[Pain case study one|Case #1]] |
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| What causes this phenomenon? Scientists believe that following amputation, nerve cells "rewire" themselves and continue to receive messages, resulting in a remapping of the brain's circuitry. The brain's ability to restructure itself, to change and adapt following injury, is called plasticity (see section on Plasticity).
| | ==Related Chapters== |
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| Our understanding of phantom pain has improved tremendously in recent years. Investigators previously believed that brain cells affected by amputation simply died off. They attributed sensations of pain at the site of the amputation to irritation of nerves located near the limb stump. Now, using imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI), scientists can actually visualize increased activity in the brain's cortex when an individual feels phantom pain. When study participants move the stump of an amputated limb, neurons in the brain remain dynamic and excitable. Surprisingly, the brain's cells can be stimulated by other body parts, often those located closest to the missing limb.
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| Treatments for phantom pain may include analgesics, anticonvulsants, and other types of drugs; nerve blocks; electrical stimulation; psychological counseling, biofeedback, hypnosis, and acupuncture; and, in rare instances, surgery.
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| ===Pain asymbolia=== | |
| Pain science acknowledges, in a puzzling challenge to IASP definition,<ref name="IASPterms">See [http://www.iasp-pain.org/AM/Template.cfm?Section=General_Resource_Links&Template=/CM/HTMLDisplay.cfm&ContentID=3058 IASP Pain Terminology]. The whole entry on the term pain itself reads like this:
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| <blockquote>
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| Pain. An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Note: The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life. Biologists recognize that those stimuli which cause pain are liable to damage tissue. Accordingly, pain is that experience we associate with actual or potential tissue damage. It is unquestionably a sensation in a part or parts of the body, but it is also always unpleasant and therefore also an emotional experience. Experiences which resemble pain but are not unpleasant, e.g., pricking, should not be called pain. Unpleasant abnormal experiences (dysesthesias) may also be pain but are not necessarily so because, subjectively, they may not have the usual sensory qualities of pain. Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. If they regard their experience as pain and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain. This definition avoids tying pain to the stimulus. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause.
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| </blockquote>
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| </ref> that pain may be experienced as a sensation devoid of any unpleasantness: this happens in a syndrome called [[pain asymbolia]] or pain dissociation, caused by conditions like lobotomy, cingulotomy or morphine analgesia. Typically, such patients report that they have pain but are not bothered by it, they recognize the sensation of pain but are mostly or completely immune to suffering from it.<ref name="asymbolia"> Nikola Grahek, [http://docserver.bis.uni-oldenburg.de/publikationen/bisverlag/2001/grafee01/grafee01.html Feeling pain and being in pain], Oldenburg, 2001. ISBN 3-8142-0780-7.</ref>
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| ===Insensitivity to pain===
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| The ability to experience pain is essential for protection from injury, and recognition of the presence of injury. Insensitivity to pain may occur in special circumstances, such as for an athlete in the heat of the action, or for an injured soldier happy to leave the battleground. This phenomenon is now explained by the [[gate control theory]]. However, insensitivity to pain may also be an acquired impairment following conditions such as spinal cord injury, diabetes mellitus, or more rarely Hansen's Disease ([[leprosy]]).<ref name=Brand_1997>{{cite book | last = Brand | first = Paul | authorlink = Paul Wilson Brand | coauthors = Philip Yancey | title = The gift of pain : why we hurt & what we can do about it | publisher = Zondervan Publ. | date = c1997 | isbn = 0-310-22144-7}}</ref> A few people can also suffer from [[congenital insensitivity to pain]], or congenital analgesia, a rare genetic defect that puts these individuals at constant risk from the consequences of unrecognized injury or illness. Children with this condition suffer carelessly repeated damages to their tongue, eyes, bones, skin, muscles. They may attain adulthood, but they have a shortened life expectancy.
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| ===Psychogenic pain===
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| Psychogenic pain, also called ''psychalgia'' or ''somatoform pain'', is physical pain that is caused, increased, or prolonged by mental, emotional, or behavioral factors.<ref name="cleveland">[http://my.clevelandclinic.org/services/Pain_Management/hic_Psychogenic_Pain.aspx Cleveland Clinic, Health information]</ref><ref>{{cite web|url=http://www.biology-online.org/dictionary/Psychogenic_pain |title=Psychogenic pain - definition from Biology-Online.org |publisher=Biology-online.org |date= |accessdate=2008-11-05}}</ref> Headache, back pain, or stomach pain are some of the most common types of psychogenic pain.<ref name="cleveland"/> Sufferers are often stigmatized, because both medical professionals and the general public tend to think that pain from a psychological source is not "real". However, specialists consider that it is no less actual or hurtful than pain from other sources.
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| ==What is the Future of Pain Research?==
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| In the forefront of pain research are scientists supported by the National Institutes of Health (NIH), including the NINDS. Other institutes at NIH that support pain research include the National Institute of Dental and Craniofacial Research, the National Cancer Institute, the National Institute of Nursing Research, the National Institute on Drug Abuse, and the National Institute of Mental Health. Developing better pain treatments is the primary goal of all pain research being conducted by these institutes.
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| Some pain medications dull the patient's perception of pain. Morphine is one such drug. It works through the body's natural pain-killing machinery, preventing pain messages from reaching the brain. Scientists are working toward the development of a morphine-like drug that will have the pain-deadening qualities of morphine but without the drug's negative side effects, such as sedation and the potential for addiction. Patients receiving morphine also face the problem of morphine tolerance, meaning that over time they require higher doses of the drug to achieve the same pain relief. Studies have identified factors that contribute to the development of tolerance; continued progress in this line of research should eventually allow patients to take lower doses of morphine.
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| One objective of investigators working to develop the future generation of pain medications is to take full advantage of the body's pain "switching center" by formulating compounds that will prevent pain signals from being amplified or stop them altogether. Blocking or interrupting pain signals, especially when there is no injury or trauma to tissue, is an important goal in the development of pain medications. An increased understanding of the basic mechanisms of pain will have profound implications for the development of future medicines. The following areas of research are bringing us closer to an ideal pain drug.
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| ===Systems and Imaging:===
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| The idea of mapping cognitive functions to precise areas of the brain dates back to phrenology, the now archaic practice of studying bumps on the head. Positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and other imaging technologies offer a vivid picture of what is happening in the brain as it processes pain. Using imaging, investigators can now see that pain activates at least three or four key areas of the brain's cortex-the layer of tissue that covers the brain. Interestingly, when patients undergo hypnosis so that the unpleasantness of a painful stimulus is not experienced, activity in some, but not all, brain areas is reduced. This emphasizes that the experience of pain involves a strong emotional component as well as the sensory experience, namely the intensity of the stimulus.
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| ===Channels:===
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| The frontier in the search for new drug targets is represented by channels. Channels are gate-like passages found along the membranes of cells that allow electrically charged chemical particles called ions to pass into the cells. Ion channels are important for transmitting signals through the nerve's membrane. The possibility now exists for developing new classes of drugs, including pain cocktails that would act at the site of channel activity.
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| ===Trophic Factors:===
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| A class of "rescuer" or "restorer" drugs may emerge from our growing knowledge of trophic factors, natural chemical substances found in the human body that affect the survival and function of cells. Trophic factors also promote cell death, but little is known about how something beneficial can become harmful. Investigators have observed that an over-accumulation of certain trophic factors in the nerve cells of animals results in heightened pain sensitivity, and that some receptors found on cells respond to trophic factors and interact with each other. These receptors may provide targets for new pain therapies.
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| ===Molecular Genetics:===
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| Certain genetic mutations can change pain sensitivity and behavioral responses to pain. People born genetically insensate to pain-that is, individuals who cannot feel pain-have a mutation in part of a gene that plays a role in cell survival. Using "knockout" animal models-animals genetically engineered to lack a certain gene-scientists are able to visualize how mutations in genes cause animals to become anxious, make noise, rear, freeze, or become hypervigilant. These genetic mutations cause a disruption or alteration in the processing of pain information as it leaves the spinal cord and travels to the brain. Knockout animals can be used to complement efforts aimed at developing new drugs.
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| ===Plasticity:===
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| Following injury, the nervous system undergoes a tremendous reorganization. This phenomenon is known as plasticity. For example, the spinal cord is "rewired" following trauma as nerve cell axons make new contacts, a phenomenon known as "sprouting." This in turn disrupts the cells' supply of trophic factors. Scientists can now identify and study the changes that occur during the processing of pain. For example, using a technique called polymerase chain reaction, abbreviated PCR, scientists can study the genes that are induced by injury and persistent pain. There is evidence that the proteins that are ultimately synthesized by these genes may be targets for new therapies. The dramatic changes that occur with injury and persistent pain underscore that chronic pain should be considered a disease of the nervous system, not just prolonged acute pain or a symptom of an injury. Thus, scientists hope that therapies directed at preventing the long-term changes that occur in the nervous system will prevent the development of chronic pain conditions.
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| ===Neurotransmitters:===
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| Just as mutations in genes may affect behavior, they may also affect a number of neurotransmitters involved in the control of pain. Using sophisticated imaging technologies, investigators can now visualize what is happening chemically in the spinal cord. From this work, new therapies may emerge, therapies that can help reduce or obliterate severe or chronic pain.
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| ==Hope for the Future==
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| Thousands of years ago, ancient peoples attributed pain to spirits and treated it with mysticism and incantations. Over the centuries, science has provided us with a remarkable ability to understand and control pain with medications, surgery, and other treatments. Today, scientists understand a great deal about the causes and mechanisms of pain, and research has produced dramatic improvements in the diagnosis and treatment of a number of painful disorders. For people who fight every day against the limitations imposed by pain, the work of NINDS-supported scientists holds the promise of an even greater understanding of pain in the coming years. Their research offers a powerful weapon in the battle to prolong and improve the lives of people with pain: hope.
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| == References ==
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| {{Reflist|2}}
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| ==See Also==
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