What Is Complex Regional Pain Syndrome (CRPS)?

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Complex regional pain syndrome (CRPS) is a chronic pain condition that is believed to be the result of dysfunction in the central or peripheral nervous systems. Older terms used to describe complex regional pain syndrome are:

Causalgia was a term first used during the Civil War to describe the intense, hot pain felt by some veterans long after their wounds had healed.

Typical features of complex regional pain syndrome include dramatic changes in the color and temperature of the skin over the affected limb or body part, accompanied by:

  • Intense burning pain
  • Skin sensitivity
  • Sweating
  • Swelling

CRPS I is frequently triggered by tissue injury; the term describes all patients with the above symptoms but with no underlying nerve injury. People with CRPS II experience the same symptoms but their cases are clearly associated with a nerve injury. Complex regional pain syndrome can strike at any age and affects both men and women, although most experts agree that it is more common in young women.


The key symptom of complex regional pain syndrome is continuous, intense pain out of proportion to the severity of the injury (if an injury has occurred), which gets worse rather than better over time. Complex regional pain syndrome most often affects one of the extremities such as:

  • Arms
  • Legs
  • Hands
  • Feet

Complex regional pain syndrome is also often accompanied by:

  • "Burning" pain
  • Increased skin sensitivity
  • Changes in skin temperature: warmer or cooler compared to the opposite extremity
  • Changes in skin color: often blotchy, purple, pale, or red
  • Changes in skin texture: shiny and thin, and sometimes excessively sweaty
  • Changes in nail and hair growth patterns
  • Swelling and stiffness in affected joints
  • Motor disability, with decreased ability to move the affected body part

Often the pain spreads to include the entire arm or leg, even though the initiating injury might have been only to a finger or toe. Pain can sometimes even travel to the opposite extremity. It may be heightened by emotional stress.

The symptoms of complex regional pain syndrome vary in severity and length. Some experts believe there are three stages associated with complex regional pain syndrome, marked by progressive changes in the skin, muscles, joints, ligaments, and bones of the affected area, although this progression has not yet been validated by clinical research studies.

  • Stage one is thought to last from 1 to 3 months and is characterized by severe, burning pain, along with muscle spasm, joint stiffness, rapid hair growth, and alterations in the blood vessels that cause the skin to change color and temperature.
  • Stage two lasts from 3 to 6 months and is characterized by intensifying pain, swelling, decreased hair growth, cracked, brittle, grooved, or spotty nails, softened bones, stiff joints, and weak muscle tone.
  • In stage three the syndrome progresses to the point where changes in the skin and bone are no longer reversible. Pain becomes unyielding and may involve the entire limb or affected area. There may be marked muscle loss (atrophy), severely limited mobility, and involuntary contractions of the muscles and tendons that flex the joints. Limbs may become contorted.


Doctors aren’t sure what causes complex regional pain syndrome. In some cases, the sympathetic nervous system plays an important role in sustaining the pain. The most recent theories suggest that pain receptors in the affected part of the body become responsive to a family of nervous system messengers known as catecholamines.

Animal studies indicate that norepinephrine, a catecholamine released from sympathetic nerves, acquires the capacity to activate pain pathways after tissue or nerve injury. The incidence of sympathetically maintained pain in complex regional pain syndrome is not known. Some experts believe that the importance of the sympathetic nervous system depends on the stage of the disease.

Another theory is that post-injury complex regional pain syndrome (CRPS II) is caused by a triggering of the immune response, which leads to the characteristic inflammatory symptoms of redness, warmth, and swelling in the affected area. Complex regional pain syndrome may, therefore, represent a disruption of the healing process. In all likelihood, complex regional pain syndrome does not have a single cause but is rather the result of multiple causes that produce similar symptoms.


Complex regional pain syndrome (CRPS) is diagnosed primarily through observation of the signs and symptoms. But because many other conditions have similar symptoms, it can be difficult for doctors to make a firm diagnosis of complex regional pain syndrome early in the course of the disorder when symptoms are few or mild. Or, for example, a simple nerve entrapment can sometimes cause pain severe enough to resemble complex regional pain syndrome. Diagnosis is further complicated by the fact that some people will improve gradually over time without treatment.

Since there is no specific diagnostic test for complex regional pain syndrome, the most important role for testing is to help rule out other conditions. Some clinicians apply a stimulus to the area to see if it causes pain such as:

  • Touch
  • Pinpricks
  • Heat
  • Cold

Doctors may also use triple-phase bone scans to identify changes in the bone and in blood circulation.


Because there is no cure for complex regional pain syndrome, treatment is aimed at relieving painful symptoms so that people can resume their normal lives. The following therapies are often used:

  • Physical therapy: A gradually increasing physical therapy or exercise program to keep the painful limb or body part moving may help restore some range of motion and function.
  • Psychotherapy: Complex regional pain syndrome often has profound psychological effects on people and their families. Those with complex regional pain syndrome may suffer from depression, anxiety, or post-traumatic stress disorder, all of which heighten the perception of pain and make rehabilitation efforts more difficult.
  • Sympathetic nerve block: Some patients will get significant pain relief from sympathetic nerve blocks. Sympathetic blocks can be done in a variety of ways. One technique involves the intravenous administration of phentolamine, a drug that blocks sympathetic receptors. Another technique involves the placement of an anesthetic next to the spine to directly block the sympathetic nerves.
  • Medications: Many different classes of medication are used to treat complex regional pain syndrome, including: However, no single drug or combination of drugs has produced consistent long-lasting improvement in symptoms.
    Topical analgesic drugs that act locally on painful nerves, skin, and muscles
  • Antiseizure drugs
  • Antidepressants
  • Corticosteroids
  • Opioids
  • Surgical sympathectomy: The use of surgical sympathectomy, a technique that destroys the nerves involved in complex regional pain syndrome, is controversial. Some experts think it is unwarranted and makes complex regional pain syndrome worse; others report a favorable outcome. Sympathectomy should be used only in patients whose pain is dramatically relieved (although temporarily) by selective sympathetic blocks.
  • Spinal cord stimulation: The placement of stimulating electrodes next to the spinal cord provides a pleasant tingling sensation in the painful area. This technique appears to help many patients with their pain.
  • Intrathecal drug pumps: These devices administer drugs directly to the spinal fluid so that opioids and local anesthetic agents can be delivered to pain-signaling targets in the spinal cord at doses far lower than those required for oral administration. This technique decreases side effects and increases drug effectiveness.


The prognosis for complex regional pain syndrome varies from person to person. Spontaneous remission from symptoms occurs in certain people. Others can have unremitting pain and crippling, irreversible changes in spite of treatment. Some doctors believe that early treatment is helpful in limiting the disorder, but this belief has not yet been supported by evidence from clinical studies. More research is needed to understand the causes of complex regional pain syndrome, how it progresses, and the role of early treatment.

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  • NIH Publication No. 04-4173 (edited).