What is complex regional pain syndrome?

Complex regional pain syndrome (CRPS) is a chronic (lasting greater than six months) pain condition that most often affects one limb (arm, leg, hand, or foot) usually after an injury.  CRPS is believed to be caused by damage to, or malfunction of, the peripheral and central nervous systems.  The central nervous system is composed of the brain and spinal cord; the peripheral nervous system involves nerve signaling from the brain and spinal cord to the rest of the body.  CRPS is characterized by prolonged or excessive pain and changes in skin color, temperature, and/or swelling in the affected area.

CRPS is divided into two types:  CRPS-I and CRPS-II. Individuals without a confirmed nerve injury are classified as having CRPS-I (previously known as reflex sympathetic dystrophy syndrome).  CRPS-II (previously known as causalgia) is when there is an associated, confirmed nerve injury.  As some research has identified evidence of nerve injury in CRPS-I, it is unclear if this disorders will always be divided into two types.  Nonetheless, the treatment is similar.

CRPS symptoms vary in severity and duration, although some cases are mild and eventually go away.  In more severe cases, individuals may not recover and may have long-term disability.

What are the symptoms of CRPS?

The key symptom is prolonged severe pain that may be constant.  It has been described as “burning,” “pins and needles” sensation, or as if someone were squeezing the affected limb.  The pain may spread to the entire arm or leg, even though the injury might have only involved a finger or toe. In rare cases, pain can sometimes even travel to the opposite extremity.  There is often increased sensitivity in the affected area, known as allodynia, in which normal contact with the skin is experienced as very painful.

People with CRPS also experience changes in skin temperature, skin color, or swelling of the affected limb.  This is due to abnormal microcirculation caused by damage to the nerves controlling blood flow and temperature.  As a result, an affected arm or leg may feel warmer or cooler compared to the opposite limb.  The skin on the affected limb may change color, becoming blotchy, blue, purple, pale, or red.

Other common features of CRPS include:

  • changes in skin texture on the affected area; it may appear shiny and thin

  • abnormal sweating pattern in the affected area or surrounding areas

  • changes in nail and hair growth patterns

  • stiffness in affected joints

  • problems coordinating muscle movement, with decreased ability to move the affected body part

  • abnormal movement in the affected limb, most often fixed abnormal posture (called dystonia) but also tremors in or jerking of the limb.

What causes CRPS?

It is unclear why some individuals develop CRPS while others with similar trauma do not.  In more than 90% of cases, the condition is triggered by a clear history of trauma or injury.  The most common triggers are fractures, sprains/strains, soft tissue injury (such as burns, cuts, or bruises), limb immobilization (such as being in a cast), surgery, or even minor medical procedures such as needle stick. CRPS represents an abnormal response that magnifies the effects of the injury.  Some people respond excessively to a trigger that causes no problem for other people, such as what is observed in people who have food allergies.

Peripheral nerve abnormalities found in individuals with CRPS usually involve the small unmyelinated and thinly myelinated sensory nerve fibers (axons) that carry pain messages and signals to blood vessels. (Myelin is a mixture of proteins and fat-like substances that surround and insulate some nerve fibers.) Because small fibers in the nerves communicate with blood vessels, injuries to the fibers may trigger the many different symptoms of CRPS.  Molecules secreted from the ends of hyperactive small nerve fibers are thought to contribute to inflammation and blood vessel abnormalities.  These peripheral nerve abnormalities in turn trigger damage in the spinal cord and brain.

Blood vessels in the affected limb may dilate (open wider) or leak fluid into the surrounding tissue, causing red, swollen skin.  The dilation and constriction of small blood vessels is controlled by small nerve fiber axons as well as chemical messengers in the blood.  The underlying muscles and deeper tissues can become starved of oxygen and nutrients, which causes muscle and joint pain as well as damage.  The blood vessels may over-constrict (clamp down), causing old, white, or bluish skin.

CRPS also affects the immune system. High levels of inflammatory chemicals (cytokines) have been found in the tissues of people with CRPS.  These contribute to the redness, swelling, and warmth reported by many patients. CRPS is more common in individuals with other inflammatory and autoimmune conditions such as asthma.

Limited data suggest that CRPS also may be influenced by genetics.  Rare family clusters of CRPS have been reported.  Familial CRPS may be more severe with earlier onset, greater dystonia, and more than one limb being affected.

Occasionally CRPS develops without any known injury.  In these cases, an infection, a blood vessel problem, or entrapment of the nerves may have caused an internal injury.  A physician will perform a thorough examination in order to identify a cause.

In many cases, CRPS results from a variety of causes.  In such instances, treatments are directed at all of the contributing factors.

How is CRPS diagnosed?

Currently there is no specific test that can confirm CRPS. Its diagnosis is based on a person’s medical history, and signs and symptoms that match the definition.  Since other conditions can cause similar symptoms, careful examination is important.  As most people improve gradually over time, the diagnosis may be more difficult later in the course of the disorder.

Testing also may be used to help rule out other conditions, such as arthritis, Lyme disease, generalized muscle diseases, a clotted vein, or small fiber polyneuropathies, because these require different treatment.  The distinguishing feature of CRPS is that of an injury to the affected area.  Such individuals should be carefully assessed so that an alternative treatable disorder is not overlooked.

Magnetic resonance imaging or triple-phase bone scans may be requested to help confirm a diagnosis.  While CRPS is often associated with excess bone resorption, a process in which certain cells break down the bone and release calcium into the blood, this finding may be observed in other illnesses as well.

What is the prognosis?

The outcome of CRPS is highly variable.  Younger persons, children, and teenagers tend to have better outcomes.  While older people can have good outcomes, there are some individuals who experience severe pain and disability despite treatment.  Anecdotal evidence suggests early treatment, particularly rehabilitation, is helpful in limiting the disorder, a concept that has not yet been proven in clinical studies.  More research is needed to understand the causes of CRPS, how it progresses, and the role of early treatment.