Epidemiology

Complex regional pain syndrome, commonly abbreviated as CRPS, is a relatively rare condition, but it occurs more often than many people realize. Studies estimate that between 5 and 26 new cases emerge for every 100,000 people each year in the United States, translating to roughly 50,000 to 200,000 new cases annually across the country.^[1][2][3] Because the diagnostic criteria have changed over the years and because the condition can be misdiagnosed or overlooked, these numbers may actually underestimate the true incidence.^[4]

The condition shows a clear pattern when it comes to who it affects. Women are three to four times more likely to develop CRPS than men, and the peak age for onset falls between 40 and 70 years.^[5][6][7] However, CRPS does not discriminate by age—it can affect people at any stage of life, including children and teenagers. In fact, younger individuals and those in good overall health tend to have better recovery outcomes compared to older adults.^[8]

Among adults, the arm and hand are the most commonly affected body parts. In children, however, the leg is more frequently involved.^[9] Research also shows that about 66 to 80 percent of cases occur in people of European ancestry, suggesting that genetic or environmental factors may play a role in susceptibility.^[10]

One particularly striking statistic involves people who suffer fractures. Among patients with a Colles fracture (a break in the wrist bone), approximately 3 to 7 percent go on to develop CRPS, depending on the study and criteria used.^[11][12] This highlights how even a common injury can trigger a disproportionate and long-lasting pain response in certain individuals.

Causes

The exact cause of complex regional pain syndrome remains largely a mystery, but researchers have identified several patterns that offer clues. In more than 90 percent of cases, CRPS is triggered by an injury or trauma to the affected limb.^[13] This could be something as major as a broken bone or as minor as a deep wound, surgery, or even a routine blood draw.^[14] In some cases, the traumatic event is so minor that patients cannot recall it happening.^[15]

What makes CRPS unusual is that the pain and other symptoms are far more severe and long-lasting than the original injury would normally cause. Most people heal from a sprained ankle or a surgical incision within weeks or months, but those who develop CRPS continue to experience intense pain, swelling, and other changes long after the tissues have healed.^[16]

CRPS can also occur without a clear physical injury. In some instances, it develops after a stroke, heart attack, or spinal cord injury.^[17] This suggests that the condition is not simply about damage to the affected body part, but rather involves complex changes in how the nervous system processes and responds to pain signals.^[18]

Experts believe that CRPS arises from a malfunction in the body’s central nervous system (which includes the brain and spinal cord) and peripheral nervous system (which relays messages between the brain and the rest of the body).^[19] For reasons not fully understood, the nervous system reacts abnormally to the injury, creating an exaggerated pain response that does not shut off even after healing has occurred. This overreaction leads to inflammation, changes in blood flow, abnormal sweating, and a host of other symptoms that define the syndrome.^[20]

Risk Factors

Certain factors increase the likelihood of developing complex regional pain syndrome. The most significant risk factor is experiencing trauma to a limb. Fractures, surgeries, penetrating injuries such as deep wounds, and even minor procedures like carpal tunnel surgery have all been linked to CRPS.^[21][22] In fact, any event that damages the small nerve fibers—those thin, unmyelinated fibers responsible for transmitting pain, temperature, and controlling blood vessels—can potentially trigger the condition.^[23]

Lifestyle and health conditions also play a role. Smoking and diabetes make recovery from CRPS especially difficult, as both conditions impair circulation and nerve health.^[24] People who have previously undergone chemotherapy are also at higher risk, likely because chemotherapy can damage nerves throughout the body.^[25] On the other hand, younger people, children, and healthy older adults with good circulation and nutrition tend to have better outcomes and a higher chance of recovery.^[26]

Gender and age are also important factors. As mentioned earlier, women are far more likely to develop CRPS than men, and the condition most commonly appears in people aged 40 to 70.^[27] While researchers are not entirely sure why women are at higher risk, hormonal differences, immune system variations, and differences in pain perception may all contribute.^[28]

There is also evidence that certain genetic or ethnic backgrounds may increase susceptibility. A large majority of CRPS cases occur in individuals of European ancestry, suggesting that inherited factors may influence how the nervous system responds to injury.^[29]

Symptoms

The hallmark symptom of complex regional pain syndrome is pain—severe, constant, and often described as burning, stinging, or tearing. This pain is usually felt deep inside the affected limb and is far worse than what would be expected from the original injury.^[30] Many people with CRPS rate their pain at 42 out of 50 on the McGill Pain Scale, making it one of the most painful conditions known to medicine—more severe than childbirth or limb amputation.^[31]

In addition to pain, people with CRPS often experience extreme sensitivity in the affected area. A condition called allodynia makes even gentle touch—such as the brush of clothing or a light breeze—feel intensely painful.^[32] Numbness may also occur, creating a confusing mix of too much sensation and too little.^[33]

Physical changes are also common. The skin on the affected limb may swell, change color (appearing red, purple, pale, or blotchy), or feel unusually warm or cold compared to the opposite limb.^[34] Over time, the skin may become shiny, thin, or excessively sweaty. Hair and nail growth may speed up or stop altogether.^[35]

Movement becomes difficult as well. Stiffness, muscle spasms, tremors, and weakness can all develop, making it hard to use the affected limb for everyday tasks.^[36] Joints may swell, and over time, some people experience muscle wasting or loss of bone density in the affected area.^[37]

Symptoms typically begin within four to six weeks after an injury, but they can appear without any clear trigger.^[38] The symptoms often change over time. Early on, the limb may be warm, red, and swollen. Later, it may become cold, pale, and stiff. If these later changes occur, they are often irreversible.^[39] In some cases, CRPS can spread from the original site to other parts of the body, including the opposite limb.^[40]

Prevention

While there is no guaranteed way to prevent complex regional pain syndrome, certain steps may reduce the risk of developing the condition, especially after an injury or surgery. One promising finding comes from research on vitamin C. Studies suggest that taking 500 milligrams of vitamin C daily for 50 days following a fracture or surgery may lower the risk of developing CRPS.^[41] Although more research is needed, this simple and low-cost intervention may offer some protection.

Maintaining overall health is another key preventive strategy. Quitting smoking and managing conditions like diabetes can improve circulation and nerve health, which in turn may reduce the likelihood of CRPS or improve outcomes if it does develop.^[42] Good nutrition, regular physical activity, and managing stress also support a healthy nervous system and may help the body respond better to injury.^[43]

After an injury or surgery, it is important not to over-rest the affected limb. While it may seem logical to avoid using a painful or injured body part, prolonged immobilization can actually increase the risk of CRPS. Gentle movement and physical therapy, guided by a healthcare provider, help maintain blood flow, flexibility, and nerve function.^[44]

Early recognition of symptoms is also critical. Being aware of the warning signs of CRPS and seeking prompt medical attention if they appear can lead to earlier treatment, which dramatically improves the chances of recovery. Education about CRPS for both patients and healthcare providers can help prevent delays in diagnosis and ensure that the condition is treated aggressively from the start.^[45]

Pathophysiology

To understand complex regional pain syndrome, it helps to know how the body normally handles pain. When you injure yourself, pain signals travel from the site of injury through nerves to the spinal cord and then to the brain, where they are interpreted as pain. At the same time, the body triggers inflammation—redness, warmth, swelling—as part of the healing process. As the injury heals, the pain and inflammation gradually fade.^[46]

In people with CRPS, this process goes wrong. The pain and inflammation do not decrease as healing progresses. Instead, they remain and often intensify. This happens because the nervous system becomes dysfunctional. The peripheral nervous system, which includes the nerves that run throughout the body, starts sending exaggerated pain signals. The central nervous system, which includes the brain and spinal cord, amplifies these signals rather than dampening them.^[47]

One key problem involves damage to the small nerve fibers that lack a protective coating called myelin. These fibers are responsible for transmitting pain, temperature sensations, itching, and controlling small blood vessels and the health of surrounding tissues.^[48] When these fibers are injured, they send faulty signals that confuse the nervous system. The result is an overactive pain response that does not shut off.^[49]

The sympathetic nervous system, which controls involuntary functions like blood flow, sweating, and temperature regulation, also becomes involved. In CRPS, this system malfunctions, leading to abnormal changes in skin color, temperature, and sweating in the affected area.^[50] Blood vessels may constrict or dilate inappropriately, causing the limb to feel unusually hot or cold. Sweat glands may produce too much or too little sweat.^[51]

Inflammation plays a major role as well. The body’s immune system may react abnormally to the injury, triggering persistent inflammation that contributes to pain, swelling, and changes in skin and tissue.^[52] Over time, this chronic inflammation can lead to secondary changes in the spinal cord and brain. The nervous system becomes hypersensitive, a process known as central sensitization, in which normal sensory input is perceived as painful.^[53]

In addition to sensory changes, CRPS also affects movement. The brain relies on accurate feedback from the body to plan and execute movements. In CRPS, this feedback is distorted or missing, making it difficult for the brain to control the affected limb. Techniques like mirror therapy and graded motor imagery aim to retrain the brain by providing it with the correct visual and sensory information it needs to restore normal movement.^[54]

If CRPS is not treated early, these changes can become permanent. Muscles may waste away from disuse, bones may lose density, and the skin and tissues may undergo irreversible changes. This is why early diagnosis and aggressive treatment are so important—they can interrupt the abnormal processes and give the nervous system a chance to return to normal function.^[55]