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Overview of Pain

By

James C. Watson

, MD, Mayo Clinic College of Medicine and Science

Last full review/revision Jun 2022
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Pain is an unpleasant sensation signaling actual or possible injury.

Pain is the most common reason people seek medical care.

Pain may be sharp or dull, intermittent or constant, or throbbing or steady. Sometimes pain is very difficult to describe. Pain may be felt at a single site or over a large area. The intensity of pain can vary from mild to intolerable.

People differ remarkably in their ability to tolerate pain. One person has difficulty tolerating the pain of a small cut or bruise, but another person can tolerate pain caused by a major accident or knife wound. The ability to withstand pain varies according to mood, personality, and circumstance. In a moment of excitement during an athletic match, an athlete may not notice a severe bruise but is likely to be very aware of the pain after the match, particularly if the team lost.

Spotlight on Aging: Pain

Conditions that cause pain are common among older people. However, as people age, they complain less of pain. The reason may be a decrease in the body’s sensitivity to pain or a more stoical attitude toward pain. Some older people mistakenly think that pain is an unavoidable part of aging and thus minimize it or do not report it.

The most common cause of pain is a musculoskeletal disorder. However, many older people have chronic pain, which may have many causes.

Effects of pain may be more serious for older people:

  • Chronic pain can make them less able to function and more dependent on other people.

  • They may lose sleep and become exhausted.

  • They may lose their appetite, resulting in undernutrition.

  • Pain may prevent people from interacting with others and from going out. As a result, they can become isolated and depressed.

  • Pain can make people less active. Lack of activity can lead to loss of muscle strength and flexibility, making activity even more difficult and increasing the risk of falls.

Older People and Pain Relievers

Older people are more likely than younger people to have side effects from pain relievers (analgesics), and some side effects are more likely to be severe. Analgesics may stay in the body longer, and older people may be more sensitive to them. Many older people take several drugs, increasing the chances that a drug will interact with the analgesic. Such interactions may reduce the effectiveness of one of the drugs or increase the risk of side effects.

Older people are more likely to have health problems that increase the risk of side effects from analgesics.

Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, can have side effects. Risk of several of side effects is higher in older people, particularly if they have several other disorders or are taking NSAIDs in high doses. For example, older people are more likely to have a heart or blood vessel (cardiovascular) disorder or risk factors for cardiovascular disorders. For people with these disorders or risk factors for them, taking NSAIDs increases their risk of having a heart attack or stroke and of developing blood clots in the legs or heart failure.

Older people are more likely to develop ulcers or bleeding in the digestive tract when they take NSAIDs. Doctors may prescribe a drug that helps protect the digestive tract from such damage. These drugs include proton pump inhibitors Proton pump inhibitors Stomach acid plays a role in a number of disorders of the stomach, including peptic ulcer, gastritis, and gastroesophageal reflux disease (GERD). Although the amount of acid present in the stomach... read more (such as omeprazole) and misoprostol.

When older people take NSAIDs, they should tell their doctor, who then evaluates them periodically for side effects. Doctors also recommend the following for older people if possible:

  • Taking low doses of NSAIDs

  • Taking them for only a short time

  • Taking breaks from using NSAIDs

Opioids Opioid Pain Relievers Pain relievers (analgesics) are the main drugs used to treat pain. Doctors choose a pain reliever based on the type and duration of pain and on the drug's likely benefits and risks. Most pain... read more are more likely to cause problems in older people, who appear to be more sensitive to these drugs than younger people. When some older people take an opioid for a short time, it reduces pain and enables them to function better physically, but it may impair mental functioning, sometimes causing confusion.

Opioids also increase the risk of falls, and taking opioids for a long time can increase the risk of osteoporosis and fractures. Opioids cause constipation and urinary retention, which tend to cause more problems in older people.

Older people are more likely to have conditions or take drugs that can make them more likely to have side effects from opioids, such as the following:

  • Impaired mental function (dementia): Opioids can make already impaired mental function worse.

  • Respiratory disorders (such as chronic obstructive pulmonary disease or obstructive sleep apnea): Opioids can cause people to breathe more slowly (called respiratory depression) or even stop breathing (called respiratory arrest). Respiratory arrest is often the cause of death in overdoses. Having a respiratory disorder increases the risk of respiratory depression, respiratory arrest, and death due to opioids.

  • Liver or kidney disorders: In people with a liver or kidney disorder, the body cannot process and eliminate opioids normally. As a result, the drugs may accumulate, increasing the risk of an overdose.

  • Use of other sedatives: Sedatives, including benzodiazepines (such as diazepam, lorazepam, and clonazepam), can interact with opioids and make people extremely drowsy and dizzy. Both opioids and sedatives slow breathing, and taking both slows breathing even more.

Opioids may also cause dependence and addiction.

Doctors usually treat pain with analgesics less likely to have side effects in older people. For example, acetaminophen Acetaminophen Pain relievers (analgesics) are the main drugs used to treat pain. Doctors choose a pain reliever based on the type and duration of pain and on the drug's likely benefits and risks. Most pain... read more is usually preferred to NSAIDs for treating chronic mild to moderate pain without inflammation. Certain NSAIDs (indomethacin and ketorolac) and certain opioids (such as pentazocine) are usually not given to older people because of the risk of side effects. If opioids are necessary, doctors give older people a low dose at first. The dose is increased slowly as needed, and its effects are monitored. Buprenorphine may be a good choice, especially for older people with a kidney disorder, because it may have a lower risk of side effects than other opioids.

Nondrug treatments and support from caregivers and family members can sometimes help older people manage pain and reduce the need for analgesics.

Pain pathways

Pain due to injury begins at special pain receptors scattered throughout the body. These pain receptors transmit signals as electrical impulses along nerves to the spinal cord and then upward to the brain. Sometimes the signal evokes a reflex response (see figure Reflex Arc: A No-Brainer Reflex Arc: A No-Brainer Reflex Arc: A No-Brainer ). When the signal reaches the spinal cord, a signal is immediately sent back along motor nerves to the original site of the pain, triggering the muscles to contract without involving the brain. For example, when people inadvertently touch something very hot, they immediately pull away. This reflex reaction helps prevent permanent damage. The pain signal is also sent to the brain. Only when the brain processes the signal and interprets it as pain do people become aware of the pain.

Pain receptors and their nerve pathways differ in different parts of the body. For this reason, pain sensation varies with the type and location of injury. For example, pain receptors in the skin are plentiful and capable of transmitting precise information, including where an injury is located and whether the source was sharp, such as a knife wound, or dull, such as pressure, heat, cold, or itching. In contrast, pain receptors in internal organs, such as the intestine are limited and imprecise. The intestine can be pinched, cut, or burned without generating a pain signal. However, stretching and pressure can cause severe intestinal pain, even from something as relatively harmless as a trapped gas bubble. The brain cannot identify the precise source of intestinal pain, which is difficult to locate and is likely to be felt over a large area.

Reflex Arc: A No-Brainer

A reflex arc is the pathway that a nerve reflex, such as the knee jerk reflex, follows.

  • 1. A tap on the knee stimulates sensory receptors, generating a nerve signal. The signal travels along a nerve to the spinal cord.

  • 2. In the spinal cord, the signal is transmitted from the sensory nerve to a motor nerve.

  • 3. The motor nerve sends the signal back to a muscle in the thigh.

  • 4. The muscle contracts, causing the lower leg to jerk upward.

  • 5. The entire reflex occurs without involving the brain.

Reflex Arc: A No-Brainer

Sometimes pain felt in one area of the body does not accurately represent where the problem is because the pain is referred there from another area. Pain can be referred because signals from several areas of the body often travel through the same nerve pathways in the spinal cord and brain. For example, pain from a heart attack may be felt in the neck, jaws, arms, or abdomen. Pain from a gallbladder attack may be felt in the back of the shoulder.

What Is Referred Pain?

Pain felt in one area of the body does not always represent where the problem is because the pain may be referred there from another area. For example, pain produced by a heart attack may feel as if it is coming from the arm because sensory information from the heart and the arm converge on the same nerve pathways in the spinal cord.

What Is Referred Pain?

Acute versus chronic pain

When severe, acute pain may cause anxiety, a rapid heart rate, an increased breathing rate, elevated blood pressure, sweating, and dilated pupils. Usually, chronic pain does not have these effects, but it may result in other problems, such as depression, disturbed sleep, decreased energy, a poor appetite, weight loss, decreased sex drive, and loss of interest in activities.

Causes of Pain

Different types of pain have different causes.

Nociceptive pain results from stimulation of pain receptors. It is caused by an injury to body tissues. Most pain, particularly acute pain, is nociceptive pain.

In diabetes, nerves outside the brain and spinal cord (peripheral nerves) are damaged. Symptoms include numbness, tingling, and pain in the toes, feet, and sometimes hands.

In postherpetic neuralgia, the area where the rash first occurred becomes painful and tender to the touch.

Nociceptive or neuropathic pain or both may be involved in acute or chronic pain. For example, chronic low back pain and most cancer pain Pain At first, cancer, as a tiny mass of cells, causes no symptoms whatsoever (see also Overview of Cancer). As a cancer grows, its physical presence can affect nearby tissues (see also Warning Signs... read more are caused mainly by ongoing stimulation of pain receptors (nociceptive pain). But in these disorders, pain can also result from nerve damage (neuropathic pain).

Psychologic factors, such as depression Depression A short discussion of prolonged grief disorder. Depression is a feeling of sadness and/or a decreased interest or pleasure in activities that becomes a disorder when it is intense enough to... read more , can also contribute to pain. Psychologic factors often affect how people feel pain and how intense it seems, but these factors are rarely the only cause of pain.

Evaluation of Pain

To evaluate a person with pain, doctors ask the person about the history and characteristics of the pain and its effect on how well the person can function. The person’s answers help them identify the cause and develop a treatment strategy. Questions can include the following:

  • Where is the pain?

  • What is the pain like (for example, is it sharp, dull, crampy)?

  • When did the pain start? Was there any injury?

  • How did the pain start? Did it begin suddenly or gradually?

  • Is the pain always present, or does it come and go?

  • Does it occur predictably after certain activities (such as meals or physical exertion) or in certain body positions? What else makes the pain worse?

  • What, if anything, helps relieve the pain?

  • Does pain affect the ability to do daily activities or to interact with other people? Does it affect sleep, appetite, and bowel and bladder function? If so, how?

  • Does pain affect mood and sense of well-being? Is the pain accompanied by feelings of depression or anxiety?

To evaluate the severity of pain, doctors sometimes use a scale of 0 (none) to 10 (severe) or ask the person to describe the pain as mild, moderate, severe, or excruciating. For children or for people who have difficulty communicating (for example, because of a stroke), drawings of faces in a series—from smiling to frowning and crying—can be used to determine the severity of pain.

Pain Scales: How Bad Is the Pain?

Because severity of pain is difficult to communicate, doctors often use a pain scale to help people indicate how severe the pain is.

Pain Scales: How Bad Is the Pain?

Doctors always try to determine whether a physical disorder is causing the pain. Many chronic disorders (such as cancer Overview of Cancer A cancer is an abnormal growth of cells (usually derived from a single abnormal cell). The cells have lost normal control mechanisms and thus are able to multiply continuously, invade nearby... read more , arthritis Osteoarthritis (OA) Osteoarthritis is a chronic disorder that causes damage to the cartilage and surrounding tissues and is characterized by pain, stiffness, and loss of function. Arthritis due to damage of joint... read more Osteoarthritis (OA) , sickle cell anemia Sickle Cell Disease Sickle cell disease is an inherited genetic abnormality of hemoglobin (the oxygen-carrying protein found in red blood cells) characterized by sickle (crescent)-shaped red blood cells and chronic... read more Sickle Cell Disease , and inflammatory bowel disease Overview of Inflammatory Bowel Disease (IBD) In inflammatory bowel diseases, the intestine (bowel) becomes inflamed, often causing recurring abdominal pain and diarrhea. The two primary types of inflammatory bowel disease (IBD) are Crohn... read more ) cause pain, as do acute disorders (such as wounds, burns Burns Burns are injuries to tissue that result from heat, electricity, radiation, or chemicals. Burns cause varying degrees of pain, blisters, swelling, and skin loss. Small, shallow burns may need... read more Burns , torn muscles, broken bones Overview of Fractures A fracture is a crack or break in a bone. Most fractures result from force applied to a bone. Fractures usually result from injuries or overuse. The injured part hurts (especially when it is... read more Overview of Fractures , sprained ligaments Overview of Sprains and Other Soft-Tissue Injuries Sprains are tears in ligaments (tissues that connect one bone to another). Other soft-tissue injuries include tears in muscles (strains) and tears (ruptures) in tendons (tissues that connect... read more Overview of Sprains and Other Soft-Tissue Injuries , appendicitis Appendicitis Appendicitis is inflammation and infection of the appendix. Often a blockage inside the appendix causes the appendix to become inflamed and infected. Abdominal pain, nausea, and fever are common... read more , kidney stones Stones in the Urinary Tract Stones (calculi) are hard masses that form in the urinary tract and may cause pain, bleeding, or an infection or block of the flow of urine. Tiny stones may cause no symptoms, but larger stones... read more Stones in the Urinary Tract , and a heart attack Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or a heart attack (myocardial infarction), depending on the location and amount... read more Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) ).

Doctors use specific techniques to check for sources of pain. Doctors move the person’s arms and legs through their normal range of motion to see if these motions cause pain. Injury, repetitive stress, chronic pain Chronic Pain Chronic pain is pain that lasts or recurs for months or years. Usually, pain is considered chronic if it does one of the following: Lasts for more than 3 months Lasts for more than 1 month after... read more , and other disorders can make certain areas of the body (called trigger points) become hypersensitive. Doctors touch various spots to see whether they are trigger points for pain. Different objects (such as a blunt key and a sharp pin) may be touched to the skin to check for loss of sensation or abnormal perceptions.

Doctors also consider emotional or mental health causes. Mental health conditions (such as depression and anxiety) can worsen pain. Because depression and anxiety may result from chronic pain, distinguishing cause and effect may be difficult. Sometimes in people with pain, there is evidence of psychologic disturbances but no evidence of a disorder that could account for the pain or its severity. Such pain is called psychogenic or psychophysiologic pain.

Doctors ask about which drugs (including over-the-counter drugs) and other treatments the person has used to treat the pain and whether they are effective. If misuse of opioids Problems with use of opioids Pain relievers (analgesics) are the main drugs used to treat pain. Doctors choose a pain reliever based on the type and duration of pain and on the drug's likely benefits and risks. Most pain... read more or other substances is suspected, further evaluation is required.

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