Pain is a distressing bodily feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage." Pain motivates animals to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Most pain resolves once the noxious stimulus is removed and the body has healed, but it may persist despite removal of the stimulus and apparent healing of the body. Sometimes pain arises in the absence of any detectable stimulus, damage or disease. Pain is the most common reason for physician consultation in most developed countries. It is a major symptom in many medical conditions, and can interfere with a person's quality of life and general functioning. People in pain experience impaired concentration, working memory, mental flexibility, problem-solving and information processing speed, and are more likely to experience irritability, depression, and anxiety. Simple over-the-counter pain medications are useful in 20% to 70% of cases of common acute pain, such as post-tooth extraction pain. Psychological factors such as social support, cognitive behavioral therapy, excitement, or distraction can affect pain's intensity or unpleasantness.
Etymology First attested in English in 1297, the word peyn comes from the Old French peine, in turn from Latin poena, meaning "punishment, penalty" (also meaning "torment, hardship, suffering" in Late Latin) and that from Greek ποινή (poine), generally meaning "price paid, penalty, punishment".
Classification In many cases, pain fits into one or a combination of three categories:
Nociceptive pain (caused by inflamed or damaged tissue that activates pain sensors called nociceptors). Nociceptive pain is divided into "superficial" and "deep" pain. Deep pains are divided into two parts: "deep physical" and "deep visceral" pain. Neuropathic pain (caused by damage or malfunction of the nervous system). Neuropathic pain is divided into "peripheral" (the source being the peripheral nervous system) and "central" (being from brain and spinal cord). Peripheral neuropathy is often described as "burning", "tingling", "electrical", "stabbing", or "pins and needles". Nociplastic pain is pain that arises despite no clear evidence of tissue or somatosensory system damage causing the pain.
In 1994, the International Association for the Study of Pain recommended using specific features to describe a patient's pain:
Region of the body involved (e.g., abdomen or lower limbs) System whose dysfunction may be causing the pain (e.g., nervous or gastrointestinal systems) Duration and pattern of occurrence Intensity Cause
Chronic versus acute
Pain is usually transitory, lasting only until the noxious stimulus is removed or the underlying damage or pathology has healed. But some painful conditions, such as rheumatoid arthritis, peripheral neuropathy, cancer, and idiopathic pain, may persist for years. Pain that lasts a long time is called "chronic" or "persistent", and pain that resolves quickly is called "acute". The International Association for the Study of Pain defines "chronic pain" as "pain that persists or recurs for longer than 3 months."
Allodynia Allodynia is pain experienced in response to an ordinarily painless stimulus. It has no biological function and is classified by characteristics of the stimuli as cold, heat, touch, pressure or a pinprick.
Phantom
Phantom pain is pain felt in a part of the body that has been amputated or from which the brain no longer receives signals. It is a type of neuropathic pain. The prevalence of phantom pain in upper limb amputees is nearly 82%, and in lower limb amputees is 54%. One study found that eight days after amputation, 72% of patients had phantom limb pain, and six months later, 67% reported it. Some amputees experience continuous pain that varies in intensity or quality; others experience several bouts of pain per day, or it may reoccur less often. It is often described as shooting, crushing, burning, or cramping. If the pain is continuous for an extended period, parts of the intact body may become sensitized, so touching them evokes pain in the phantom limb. Phantom limb pain may accompany urination or defecation. Local anesthetic injections into the nerves or sensitive areas of the stump may relieve pain for days, weeks, or sometimes permanently, despite the drug wearing off in a matter of hours, and small injections of hypertonic saline into the soft tissue between vertebrae produces local pain that radiates into the phantom limb for ten minutes or so and may be followed by hours, weeks, or even longer of partial or total relief from phantom pain. Vigorous vibration or electrical stimulation of the stump, or current from electrodes surgically implanted onto the spinal cord, all produce relief in some patients. Mirror box therapy produces the illusion of movement and touch in a phantom limb, which in turn may cause a reduction in pain. Paraplegia, the loss of sensation and voluntary motor control after serious spinal cord damage, may be accompanied by girdle pain at the level of the spinal cord damage, visceral pain evoked by a filling bladder or bowel, or, in five to ten percent of people with paraplegia, phantom body pain in areas of complete sensory loss. This phantom body pain is initially described as burning or tingling but may evolve into severe crushing or pinching pain or the sensation of fire running down the legs or of a knife twisting in the flesh. Onset may or may not occur immediately, and can happen years after the disabling injury. Surgical treatment rarely provides lasting relief.
Breakthrough Breakthrough pain is transitory pain that comes on suddenly and is not alleviated by the patient's regular pain management. It is common in cancer patients who often have background pain that is generally well-controlled by medications but who also sometimes experience bouts of severe pain that, from time to time, "breaks through" the medication. The characteristics of breakthrough cancer pain vary from person to person and according to the cause. Management of breakthrough pain can entail intensive use of opioids, including fentanyl.
Asymbolia and insensitivity
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