Complex regional pain syndrome (CRPS) is a chronic pain condition in which an arm or leg develops severe, persistent pain that is disproportionate to the original injury. It affects roughly 26 per 100,000 people per year, most commonly after fractures, surgery, or soft tissue injuries. The pain is accompanied by visible changes in the affected limb, including swelling, skin color shifts, temperature differences, and sometimes altered hair and nail growth.
How CRPS Develops
CRPS typically starts after some form of trauma. The most common triggers are fractures (especially wrist fractures), surgical procedures, and crushing injuries. But it can also follow events that seem minor or unrelated: a sprained ankle, an infection, or even a heart attack. In some cases, no clear triggering event is identified at all.
What makes CRPS unusual is that the pain and dysfunction far exceed what you’d expect from the original injury. A healed wrist fracture, for example, might leave someone with a hand that burns, swells, changes color, and can barely move, months after the bone itself has fully mended. The condition comes in two forms. Type 1 occurs without any confirmed nerve damage and accounts for the majority of cases. Type 2 involves a documented nerve injury, which distinguishes it as a form of neuropathic pain.
What Happens Inside the Body
CRPS is not simply “pain that won’t stop.” Multiple systems malfunction at once. After the initial injury, nerve fibers in the affected area release signaling molecules that trigger intense local inflammation, a process called neurogenic inflammation. This is the same mechanism involved in migraines, and it helps explain the burning quality of CRPS pain.
Over time, the problem migrates inward. Immune-like cells in the spinal cord and brain become activated and begin releasing inflammatory proteins. These proteins act as powerful amplifiers of pain signaling, increasing the responsiveness of pain-processing neurons within minutes. The result is central sensitization: the nervous system essentially turns up its volume, so that normal sensations like light touch or mild pressure register as painful. This is why people with CRPS can experience agony from something as harmless as a bedsheet brushing their skin.
The autonomic nervous system, which controls involuntary functions like blood flow, sweating, and temperature regulation, also goes haywire in the affected limb. That’s what produces the visible signs: a hand that turns red or blue, skin that feels burning hot on one side and ice cold on the other, or excessive sweating on just one limb.
Recognizing the Symptoms
CRPS produces a distinctive cluster of problems that span four categories:
- Sensory: Pain that feels burning or electric, heightened sensitivity to touch or pinprick (hyperalgesia), and pain from stimuli that shouldn’t hurt at all, like clothing or a gentle breeze (allodynia).
- Vasomotor: Noticeable temperature differences between the affected limb and the other side, along with skin color changes ranging from red and blotchy to pale or bluish.
- Sweating and swelling: The affected limb may swell significantly and sweat differently than the unaffected side.
- Motor and trophic: Reduced range of motion, weakness, tremor, or involuntary muscle contractions (dystonia). Over time, the skin texture may become shiny or thin, nails may grow abnormally fast or become ridged and brittle, and hair on the limb may grow faster or slower than normal.
For a clinical diagnosis using the widely accepted Budapest Criteria, you need to report symptoms in at least three of these four categories and show observable physical signs in at least two of them during examination. There is no single blood test or imaging scan that confirms CRPS, which is one reason diagnosis is often delayed.
Who Gets CRPS
Women are affected roughly three times as often as men. In clinical data, about 73% of patients are female. The average age at diagnosis tends to be in the 50s and 60s, though CRPS can occur at any age, including in children and adolescents. Why certain people develop CRPS after an injury while others with identical injuries do not remains poorly understood.
Treatment Approaches
Early treatment produces better outcomes, and the approach is typically multimodal, combining medication with physical rehabilitation.
Bisphosphonates, a class of drugs originally developed for bone conditions, have the strongest clinical trial evidence for reducing CRPS pain and improving physical function. They are considered a first-line treatment. In the early inflammatory phase, a short course of oral corticosteroids (typically tapered over several weeks) can also help, particularly when swelling and redness are prominent. Nerve pain medications and antidepressants are sometimes used for pain management, though the evidence specifically in CRPS is limited. Opioids are generally reserved as a second or third option.
Physical rehabilitation plays a central role but requires a careful, gradual approach because the affected limb is often too painful for conventional exercise. One of the most well-studied techniques is graded motor imagery, a three-stage program. It begins with laterality training, where you practice identifying whether pictures show a left or right hand (or foot), retraining the brain’s ability to mentally represent the affected limb. Next comes motor imagery, where you imagine moving the limb without actually doing it. The final stage is mirror therapy: you place a mirror between your limbs and watch the reflection of your healthy limb moving, creating a visual illusion that the painful limb is moving without pain. This sequence works by gradually retraining the brain’s distorted body map.
When Standard Treatment Isn’t Enough
For people whose pain doesn’t respond to medications and rehabilitation, two FDA-approved neurostimulation options exist: spinal cord stimulation and dorsal root ganglion stimulation. Both involve implanting small devices that deliver electrical signals to interrupt pain pathways. One randomized trial found spinal cord stimulation effective for pain reduction in CRPS, though its advantage over physical therapy alone faded by the five-year mark.
Ketamine infusions, administered intravenously in a hospital setting, represent another option for refractory cases. Roughly half of CRPS patients who receive ketamine infusions achieve some form of meaningful long-term pain relief. The duration of benefit varies widely, from several weeks to several months, and the treatment requires close monitoring due to side effects like sedation, hallucinations, and restlessness.
Recovery and Long-Term Outlook
The honest picture is more sobering than many sources suggest. A prospective study tracking patients over their first year found that symptom severity improved most in the first six months and then plateaued. At the one-year mark, nearly two-thirds of patients still met diagnostic criteria for CRPS, and only 5.4% were completely symptom-free. This doesn’t mean people don’t improve. Most experience meaningful reductions in pain and disability, particularly with early, aggressive treatment. But full resolution within the first year is uncommon, and CRPS often requires long-term management.
The strongest predictor of a better outcome is early intervention. The first six months appear to represent a critical window where treatment gains are largest, reinforcing the importance of prompt diagnosis.
Prevention After Injury or Surgery
One simple preventive measure has reasonable evidence behind it: vitamin C supplementation after fractures or orthopedic surgery. Both the American Academy of Orthopedic Surgeons and the Royal College of Physicians in the UK have recommended 500 mg of vitamin C daily for roughly 50 days following a wrist fracture or similar injury. Five out of six studies reviewed found that daily doses of 500 to 1,000 mg reduced the likelihood of developing CRPS. Doses below 500 mg were not effective.