Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 78. Pain

Topics: Introduction | Evaluation of Pain | Types of Pain | Treatment of Pain

Types of Pain

There are several types of pain, including nociceptive pain (such as pain after surgery and pain due to cancer), neuropathic pain (such as sciatica (see Section 6, Chapter 94)), and psychogenic pain.

Nociceptive Pain

Nociceptive pain is caused by an injury to body tissues.

The injury may be a cut, bruise, bone fracture, crush injury, burn, or anything that damages tissues. This type of pain is typically aching, sharp, or throbbing. Most pain is nociceptive pain. Pain receptors for tissue injury (nociceptors) are located mostly in the skin or in the internal organs.

The pain almost universally experienced after surgery is nociceptive pain. The pain may be constant or intermittent, often worsening when a person moves, coughs, laughs, or breathes deeply or when the dressings over the surgical wound are changed.

Most of the pain due to cancer is nociceptive. When a tumor invades bones and organs, it may cause mild discomfort or severe, unrelenting pain. Some cancer treatments, such as surgery and radiation therapy, can also cause nociceptive pain.

Neuropathic Pain

Neuropathic pain is caused by abnormalities in the nerves, spinal cord, or brain.

Neuropathic pain may be felt as a burning or tingling sensation or as hypersensitivity to touch or cold. Neuropathic pain includes such syndromes as phantom limb pain, postherpetic neuralgia, reflex sympathetic dystrophy, and causalgia.

Phantom limb pain is seemingly felt in an amputated part of the body, usually a limb. It differs from phantom limb sensation--the feeling that the amputated part is still there--which is much more common. Phantom limb pain cannot be caused by a problem in the limb; rather, it must be caused by a change in the nervous system above the site where the limb was amputated. The brain misinterprets the nerve signals as coming from the amputated limb. Usually, the pain is felt in the toes, ankle, and foot of an amputated leg or the fingers and hand of an amputated arm. The pain may resemble squeezing, burning, or crushing sensations, but it often differs from any sensation previously experienced. For some people, phantom limb pain occurs less frequently as time passes, but for others, it persists. Massage can sometimes help, but drug therapy is sometimes necessary.

Postherpetic neuralgia results from herpes zoster (shingles), which causes inflammation of nerve tissue. The pain is felt as a constant deep aching or burning, as a sharp and intermittent pain, or as hypersensitivity to touch or cold. The pain may be debilitating.

Reflex sympathetic dystrophy (complex regional pain syndrome, type 1) and causalgia (complex regional pain syndrome, type 2) are chronic pain syndromes. They are defined as persistent burning pain accompanied by certain abnormalities that occur in the same area as the pain. Abnormalities include increased or decreased sweating, swelling, changes in skin color, and damage to the skin, hair, nails, muscle, and bone (including muscle wasting and bone loss). Both syndromes typically occur after an injury. Reflex sympathetic dystrophy results from injury to tissues other than nerve tissue (as in the shoulder-hand syndrome). Causalgia results from injury to nerve tissue.

Some types of reflex sympathetic dystrophy and causalgia are made worse by activity of the sympathetic nervous system, which normally prepares the body for stressful or emergency situations--for fight or flight. For this reason, doctors suggest treatment with a sympathetic nerve block (see Section 6, Chapter 78).

Psychogenic Pain

Psychogenic pain is entirely or mostly related to a psychologic disorder.

When people have persistent pain with evidence of psychologic disturbances and without evidence of a disorder that could cause the pain, the pain may be described as psychogenic. Pain that is purely psychogenic is rare. More commonly, the pain has a physical cause, but the doctor's assessment indicates that the degree of pain and the disability experienced are out of proportion to what most people with a similar disorder experience. Sometimes this type of pain is described as a chronic pain syndrome. Psychologic factors often contribute to disability and to an exaggeration of pain complaints. Any kind of pain can be complicated by psychologic factors. Even when pain is suspected to be psychogenic, doctors still investigate whether a physical disorder is contributing to the pain.

The fact that the pain is caused or worsened by psychologic factors does not mean that it is not real. Most people who report pain are really experiencing it, even if a physical cause cannot be identified. Pain complicated by psychologic factors still requires treatment, often by a team that includes a psychologist or psychiatrist. As with other kinds of treatment for chronic pain, the treatment for this type of pain varies from person to person, and doctors try to match the treatment with the person's needs. For most people who have chronic psychogenic pain, the goals of treatment are to improve comfort and physical and psychologic function. Doctors may make specific recommendations for gradually increasing physical and social activities. Drugs and nondrug treatments--such as biofeedback, relaxation training, distraction techniques, hypnosis, transcutaneous electrical nerve stimulation (TENS), and physical therapy--may be used. Psychologic counseling is often needed.