(See also Overview of Pain.)
Complex regional pain syndrome causes neuropathic pain. In this disorder, pain signals are processed abnormally by the brain and spinal cord. It typically occurs after an injury.
There are two types of complex regional pain syndrome:
Type 1, which used to be called reflex sympathetic dystrophy, results from injury to tissues other than nerve tissue, as when bone and soft tissues (such as ligaments and tendons) are crushed in an accident. It may also develop after amputation, a heart attack, stroke, or cancer (such as cancer of the lungs, breast, ovary, or brain). Type 1 commonly occurs after an injured limb is treated with a cast or splint to immobilize it.
Type 2, which used to be called causalgia, results from injury to nerves.
Sometimes there is no obvious cause.
Both types occur most often in young adults and are 2 or 3 times more common among women.
Sometimes complex regional pain syndrome occurs when the sympathetic nervous system becomes overactive. The sympathetic nervous system normally prepares the body for stressful or emergency situations—for fight or flight.
Symptoms of complex regional pain syndrome vary greatly and do not follow a pattern.
Pain—burning or aching—is common. It usually occurs in the limb (arm, leg, hand, or foot) that was injured. The pain is often worse than what would be expected from the injury. Emotional stress or changes in the temperature may make the pain worse. The skin in the affected area often becomes very sensitive to the touch (called allodynia). As a result, normal contact with the skin is experienced as very painful.
People may not use the affected limb because of the pain. As result, people may be unable to move a joint normally, through its normal range of motion. Muscles may become permanently shortened and stiff (called contractures), and scar tissue may form.
The affected limb may swell. Hair may be lost. The nails may crack or become thick. Bones may become less dense. Muscles may waste away and become weak.
People may sweat more or less than usual and may feel hotter or cooler than usual. The skin in the affected area may look, red, blotchy, pale, or shiny.
The fingers may flex or the foot may twist in an abnormal position and may remain that way (called dystonia). The affected limb may tremble or jerk.
Many people with complex regional pain syndrome become depressed, anxious, and/or angry, partly because the cause is poorly understood, the effectiveness of treatments is limited, and the outcome is hard to predict.
Symptoms may lessen or remain the same for years. In a few people, the disorder progresses, spreading to other areas of the body.
Doctors diagnose complex regional pain syndrome based on specific symptoms in the affected limb. These symptoms include the following:
Pain that is greater than expected for the injury
Sensitivity to touch
Certain changes in the skin's appearance or temperature
Increased or decreased sweating or swelling
Hair loss and cracked or thickened nails
Reduced range of motion, muscle weakness, and/or abnormal movements (such as trembling or jerking of the affected limb)
If the diagnosis is unclear, doctors may take x-rays or do a bone scan to look for bone loss or inflammation.
Usually, a combination of treatments is used to treat complex regional pain syndrome. Treatment aims to help people move the affected limb more.
Physical therapy can help in the following ways:
In some people, a sympathetic nerve block can relieve pain if it is caused by overactivity of the sympathetic nervous system. In such cases, it may be needed to make physical therapy possible. Oral pain relievers (analgesics), including nonsteroidal anti-inflammatory drugs (NSAIDs), opioids, and various adjuvant analgesics (such as antiseizure drugs and antidepressants), may also relieve pain well enough to make physical therapy possible.
Nerves or the spinal cord can be electrically stimulated (called neuromodulation) to reduce the pain's intensity.
Spinal cord stimulation involves surgically placing a spinal cord stimulator (a device that generates electrical impulses) under the skin, usually in a buttock or abdomen. Small wires (leads) from the device are placed in the space around the spinal cord (epidural space). These impulses change the way pain signals are sent to the brain and thus change how unpleasant symptoms are perceived.
Transcutaneous electrical nerve stimulation (TENS) can also be used, but there is far less evidence for its effectiveness than there is for spinal cord stimulation. TENS involves placing electrodes on the skin rather than placing a device under the skin. The electrodes produce a low current that causes tingling but does not cause muscles to contract.
Desensitization is also helpful. This procedure involves touching the painful part with something that does not usually irritate the skin (such as silk). Then, over a period of time, doctors use increasingly irritating materials (such as denim). Desensitization can also involve placing the affected limb in a cool water bath, then in a warm water bath.
Mirror therapy may help people with complex regional pain syndrome. A health care practitioner teaches people how to use this therapy. People sit with a large mirror facing their unaffected limb and hiding their affected limb. The mirror reflects the image of the unaffected limb, giving people the impression that they have two normal limbs. People are then instructed to move the unaffected limb while watching its reflected image. Thus, people feel as if they are moving two normal limbs. If people do this exercise for 30 minutes a day for 4 weeks, pain may be substantially reduced. This therapy changes the pathways in the brain that interpret pain signals in the body.
Psychologic therapy may also be used when people with complex regional pain syndrome also have depression and anxiety.
Acupuncture may help relieve the pain.