Neuropathic pain is usually caused by damage to or dysfunction of the nerves, spinal cord, or brain.
Neuropathic pain may be felt as burning or tingling or as hypersensitivity to touch or cold. Causes include compression of a nerve (for example, by a tumor,
by a ruptured intervertebral disk, or as occurs in carpal tunnel syndrome), nerve damage (for example, as occurs in a metabolic disorder such as diabetes
mellitus), and abnormal or disrupted processing of pain signals by the brain and spinal cord. Processing of pain is abnormal in phantom limb pain,
postherpetic neuralgia, and complex regional pain syndrome.
Phantom Limb Pain:
Pain seems to be 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. But the brain misinterprets the nerve signals as coming from the
amputated limb. Usually, the pain seems to be in the toes, ankle, and foot of an amputated leg or in 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.
This disorder results from herpes zoster (shingles, which causes inflammation of nerve tissue), but occurs
only after shingles resolves. What causes postherpetic neuralgia is unknown. 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.
Complex Regional Pain Syndrome:
This chronic pain syndrome is 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, damage to the skin, hair loss,
cracked or thickened nails, muscle wasting and weakness, and bone loss. This syndrome typically occurs after an injury. There are two types:
Type 1, which used to be called reflex sympathetic dystrophy, results from injury to tissues other than nerve tissue, as when bone is crushed
in an accident or when heart tissue is damaged in a heart attack.
Type 2, which used to be called causalgia, results from injury to nerve tissue.
Sometimes complex regional pain syndrome is made worse by activity of the sympathetic nervous system, which normally prepares the body for stressful or
emergency situations—for fight or flight.
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 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.
Psychogenic pain is pain that is mostly related to psychologic factors.
When people have persistent pain with evidence of psychologic disturbances and without evidence of a disorder that could account for the pain or its severity,
the pain may be described as psychogenic. However, psychophysiologic pain is a more accurate term because the pain results from interaction of physical and
psychologic factors. Psychogenic pain is far less common than nociceptive or neuropathic pain.
Psychologic factors often contribute to chronic pain and may contribute to pain-related disability. In such cases,
the pain, disability, or both usually have a physical cause, but psychologic factors exaggerate or enhance the pain, making it worse than what most people
with a similar physical disorder experience. For example, people with chronic pain know it will recur and may become fearful and anxious as they anticipate
the pain. These emotions make them more sensitive to pain. Sometimes doctors describe chronic pain that is worsened by psychologic factors as a chronic pain
Chronic Psychogenic Pain
The fact that 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. 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.