Complex regional pain syndrome (CRPS) is a chronic pain condition that typically affects one limb, usually after an injury or surgery, and produces pain far out of proportion to the original event. On the McGill Pain Scale, a CRPS pain flare scores higher than childbirth or amputation, making it one of the most intense pain conditions known. It affects roughly 26 people per 100,000 each year, and women develop it at least three times more often than men.
Type 1 vs. Type 2
CRPS comes in two forms. Type 1, formerly called reflex sympathetic dystrophy (RSD), develops without a confirmed nerve injury. This is the more common form. Type 2, historically known as causalgia, occurs when there is a verified injury to a specific nerve. Both types produce the same range of symptoms, and the distinction matters mainly for understanding the trigger rather than guiding treatment.
What Triggers CRPS
The most common triggers are fractures, surgery, sprains, and soft tissue injuries. In some cases, even a minor event like an IV insertion or a small cut can set it off. The hallmark is that the resulting pain is wildly disproportionate to whatever caused it. A healed wrist fracture, for example, may leave behind burning pain that intensifies for weeks or months instead of fading. In a small number of cases, no specific injury can be identified at all.
What Happens Inside the Body
CRPS is not a single malfunction. It involves overlapping problems in the immune system, nervous system, and the body’s autonomic controls (the systems that regulate blood flow, sweating, and temperature). No single mechanism explains it, which is part of why it’s so difficult to treat.
After the initial injury, the body releases a flood of inflammatory molecules. In CRPS, this inflammatory response doesn’t shut off the way it normally would. Elevated levels of inflammatory signaling chemicals have been found in both the blood and spinal fluid of people with CRPS. These chemicals trigger what’s called neurogenic inflammation: nerve endings themselves start releasing substances that cause blood vessels to widen and tissue to swell.
That persistent inflammation lowers the threshold for pain signals in the affected area, a process called peripheral sensitization. Nerves that would normally need a strong stimulus to fire start responding to very light touch or small temperature changes. Over time, the spinal cord itself becomes hyperexcitable. Pain signals get amplified before they even reach the brain. This is central sensitization, and it explains two of the most distressing features of CRPS: hyperalgesia (normal pain feels far worse than it should) and allodynia (things that shouldn’t hurt at all, like a breeze or clothing brushing the skin, become painful).
Brain imaging studies show that CRPS actually reshapes the brain’s body map. The area of the sensory cortex that corresponds to the affected limb shrinks, and the degree of this reorganization correlates with pain severity. The autonomic nervous system also goes haywire. Pain-sensing nerve fibers develop extra receptors for stress hormones, so the sympathetic “fight or flight” system starts directly amplifying pain. This autonomic disruption can even affect heart rate and blood pressure regulation in some people.
Recognizing the Symptoms
CRPS produces a distinctive cluster of symptoms across four categories: sensory, blood flow, sweat and swelling, and movement. The pain itself is usually burning or throbbing and continuous, though it can spike unpredictably. Beyond the pain, the visible and measurable changes to the limb are what often lead to a diagnosis.
- Sensory changes: Extreme sensitivity to touch, pressure, or temperature. A light brush across the skin or mild cold can trigger severe pain.
- Skin color and temperature: The affected limb may look red, blue, or mottled, and it often feels noticeably warmer or cooler than the other side. A temperature difference of more than 1°C between the affected and unaffected limb is considered a clinical sign. In early “warm” CRPS, the limb runs hot due to widened blood vessels. In later “cold” CRPS, blood vessels constrict and the limb becomes cool and pale or bluish.
- Swelling and sweating: The limb may swell visibly, and sweating patterns become uneven, with the affected area sweating much more or much less than the opposite side.
- Movement and tissue changes: Reduced range of motion, weakness, tremor, or involuntary muscle contractions can develop. Over time, skin texture may change, becoming thin and shiny or thick and rough. Nails may grow faster or slower, and hair growth on the limb may increase or decrease.
How CRPS Is Diagnosed
There is no single blood test or imaging scan that confirms CRPS. Diagnosis relies on clinical criteria known as the Budapest Criteria. To meet the standard for a clinical diagnosis, you need all of the following: continuing pain that is disproportionate to the triggering event, at least one reported symptom in each of the four categories listed above, and at least one observable sign (something a clinician can see or measure) in at least two of those four categories. Finally, no other condition can better explain what’s happening.
This means CRPS is partly a diagnosis of exclusion. Conditions like infections, blood clots, or nerve compression need to be ruled out first. The reliance on clinical observation rather than a definitive test contributes to delays in diagnosis, which can be costly because early treatment matters enormously.
Why Early Treatment Matters
A prospective study tracking CRPS patients over 12 months found that the greatest improvements in symptom severity happened during the first six months, then plateaued. By the one-year mark, only 5.4% of patients were completely symptom-free, and nearly two-thirds still met diagnostic criteria for CRPS. These numbers are less optimistic than older estimates, and they underline an important reality: CRPS rarely resolves on its own within the first year, and the best window for meaningful improvement is the first six months after onset.
This doesn’t mean nothing helps after six months. It means that the sooner treatment begins, the more likely it is to make a significant difference in long-term pain and function.
Treatment Approaches
There are no FDA-approved medications specifically for CRPS, so treatment is built from off-label options and rehabilitation strategies. What works varies widely from person to person, and most treatment plans combine multiple approaches.
Rehabilitation and Movement-Based Therapies
Physical and occupational therapy form the backbone of CRPS treatment. The goal is to gradually restore movement and reduce the brain’s protective pain response. One of the most studied techniques is graded motor imagery, which uses visualization and mirror therapy to retrain the brain’s distorted body map. In mirror therapy, you place a mirror between your limbs and watch the reflection of the healthy limb moving, which tricks the brain into “seeing” the affected limb move normally and without pain. Research shows that graded motor imagery and mirror therapy reduce pain by an average of 20 points on the Neuropathic Pain Scale and produce meaningful functional improvements. Mirror therapy has been especially effective for CRPS that develops after stroke, with additional benefits in reducing swelling.
Medications
Because CRPS involves so many different mechanisms, medications target different pieces of the puzzle. Anti-seizure drugs like gabapentin and pregabalin help calm overexcited nerves. Certain antidepressants are used not for mood but for their ability to dampen pain signaling in the spinal cord. Short courses of corticosteroids can reduce inflammation in early CRPS. Bisphosphonates, typically used for bone conditions, have shown benefit in CRPS for reasons that aren’t fully understood but may relate to their anti-inflammatory effects. Standard anti-inflammatory painkillers tend to have limited effectiveness on their own.
Interventional Procedures
When medications and rehabilitation aren’t enough, nerve blocks can interrupt pain signals from the sympathetic nervous system. Spinal cord stimulation, where a small device delivers electrical pulses to the spinal cord, has helped some people with treatment-resistant CRPS by disrupting pain signals before they reach the brain. Ketamine, which targets the specific brain receptors involved in central sensitization, is sometimes used in controlled settings for severe cases and has shown the ability to reduce pain rapidly while also lowering the need for opioid medications.
Success rates for these interventional options vary, and they’re generally reserved for cases that haven’t responded to more conservative approaches. The overall treatment landscape for CRPS remains challenging precisely because the condition involves so many different systems going wrong at once, and no single therapy addresses all of them.