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.
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 ). 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.
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.
Acute versus chronic pain
Pain may be acute or chronic. Acute pain means pain that begins suddenly and does not last long (days or weeks). 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 lasts for many months or years.
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.
Neuropathic pain Neuropathic Pain Neuropathic pain is caused by damage to or dysfunction of the nerves, spinal cord, or brain. (See also Overview of Pain.) Neuropathic pain may result from Compression of a nerve—for example... read more results from damage to or dysfunction of the brain or spinal cord (central nervous system) or the nerves outside the brain and spinal cord ( peripheral nervous system Overview of the Peripheral Nervous System The peripheral nervous system refers to the parts of the nervous system that are outside the central nervous system, that is, those outside the brain and spinal cord. Thus, the peripheral nervous... read more ). It may occur when
Pressure is put on a specific nerve—for example, by a tumor or a ruptured disk Herniated Disk A herniated disk occurs when the tough covering of a disk in the spine tears or ruptures. The soft, jelly-like interior of the disk may then bulge out (herniate) through the covering. Aging... read more in the spine, causing low back pain Low Back Pain Low back pain and neck pain are among the most common reasons for health care visits. The pain usually results from problems with the musculoskeletal system—most notably the spine, including... read more and/or pain radiating down the leg. Pressure on a nerve in the wrist can cause carpal tunnel syndrome Carpal Tunnel Syndrome Carpal tunnel syndrome is a painful compression (pinching) of the median nerve as it passes through the carpal tunnel in the wrist. The cause of most cases of carpal tunnel syndrome is unknown... read more .
Nerves are damaged, as occurs in diabetes mellitus Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more or postherpetic neuralgia Postherpetic Neuralgia Postherpetic neuralgia is chronic pain in areas of skin supplied by nerves infected with herpes zoster ( shingles). Shingles is a painful rash of fluid-filled blisters that is caused by reactivation... read more (pain after shingles) Shingles Shingles is a painful skin rash caused by a viral infection that results from reactivation of the varicella-zoster virus, the virus that causes chickenpox. What causes the virus to reactive... read more .
The brain and spinal cord do not process pain signals normally or something disrupts this processing, as occurs in phantom limb pain Neuropathic Pain Neuropathic pain is caused by damage to or dysfunction of the nerves, spinal cord, or brain. (See also Overview of Pain.) Neuropathic pain may result from Compression of a nerve—for example... read more and complex regional pain syndrome Complex Regional Pain Syndrome Complex regional pain syndrome is chronic neuropathic pain characterized by persistent burning or aching pain plus certain abnormalities that occur in the same area as the pain. Abnormalities... read more .
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.
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 , 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 , 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 , 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 , 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 , 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 , 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 ).
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.