It is generally agreed that complex regional pain syndrome (CRPS) is a neurological disorder affecting the central nervous system and the peripheral nervous system. A phenomenon called “central sensitization” has been thought for the basis of some of the symptoms of CRPS.

Exactly how CRPS develops remains unknown, although it usually begins with an injury. CRPS first was described during the Civil War, when patients complained of burning pain that continued long after their wounds had healed.

Some scientists believe it may result from disturbances in the sympathetic nervous system, which is the part of the nervous system that controls blood flow and sweat glands. Others suggest that it is triggered by an immune system response, which leads to the characteristic inflammatory symptoms of redness, warmth and swelling in the affected area.

CRPS may occur after a significant trauma to an arm or a leg, such as from a gunshot wound or shrapnel blast. In other cases, the injury that triggers CRPS may be so minor it goes unnoticed by the patient. Other types of trauma – including surgery, heart attacks, stroke, infections, fractures and sprains – also can trigger CRPS.

Damage to the nervous system caused by disease can trigger CRPS. Diseases of the central nervous system, such as multiple sclerosis, or damage to the peripheral nerves from conditions such as diabetes may cause CRPS in some patients.

Scientists are not sure why some injuries cause CRPS and others do not. However, factors that may contribute to the development of CRPS include:

• Genetics. The disease may run in families.
  
  
• Stress. People under stress at the time of an injury may be more likely to develop CRPS.
  
  
• Lack of use of an injured body part. Restricting the use of injured body parts because of pain or an outside factor such as a cast or sling may contribute to the development of CRPS.