Causalgia is a chronic pain condition caused by damage to a peripheral nerve, typically from a traumatic injury. It produces intense, burning pain in the affected limb along with visible changes to the skin, nails, and hair in the area. The condition is now formally called complex regional pain syndrome type II (CRPS II), a name adopted in 1994 by the International Association for the Study of Pain. What sets causalgia apart from the more common CRPS type I is that it always involves a confirmed nerve injury.
How Causalgia Got Its Name
The term causalgia comes from the Greek words for “heat” and “pain,” and it was coined during the American Civil War. Silas Weir Mitchell, a Philadelphia neurologist treating wounded soldiers, documented cases of relentless burning pain that followed gunshot wounds to major nerves. He called it “the most terrible of all the tortures which a nerve wound may inflict.”
Mitchell’s case descriptions remain striking even today. One Union soldier, shot through the arm near the elbow, developed burning pain in his palm so severe that even blowing on it was excruciating. He kept the hand constantly wrapped and wet but couldn’t tolerate pouring water directly onto his palm. Within weeks, ordinary sounds like rustling paper, footsteps, or a band playing would worsen his pain. His doctors noted that strong emotions, particularly anger or disappointment, would intensify the aching. These observations from 1864 captured features that modern clinicians still recognize as hallmarks of the condition: extreme sensitivity to touch, emotional amplification of pain, and autonomic changes like excessive sweating.
What Happens Inside the Nervous System
When a peripheral nerve is damaged, the injured fibers don’t always heal cleanly. At the site of injury, nerve membranes can develop abnormal electrical properties, essentially becoming hyperexcitable. New nerve sprouts grow into the damaged area, and these sprouts develop an unusual sensitivity to chemicals released by the sympathetic nervous system, the network that controls involuntary functions like heart rate, sweating, and blood vessel constriction.
Normally, pain-sensing fibers and sympathetic fibers operate independently. After nerve damage in causalgia, they become coupled. Stress hormones released by nearby sympathetic nerve endings stimulate the damaged sensory fibers, generating pain signals where none should exist. This is why emotional stress, temperature changes, or even loud noises can trigger or worsen the burning pain. The nervous system is essentially short-circuiting, with signals meant to regulate blood flow and sweating instead activating pain pathways.
What Causalgia Feels Like
The defining symptom is a deep, burning pain that typically begins in the area supplied by the injured nerve but can spread beyond it. The pain is often constant and can be worsened by light touch, temperature changes, movement, emotional stress, or sound. Two forms of heightened sensitivity are characteristic: ordinary touch feels painful (a condition called allodynia), and stimuli that would normally cause mild discomfort produce disproportionately intense pain.
Beyond pain, the affected limb undergoes visible physical changes that fall into four categories:
- Sensory changes: heightened sensitivity to touch and pain in the affected area
- Blood flow changes: the skin may appear mottled, red, or blue, and the limb’s temperature often differs noticeably from the opposite side
- Swelling and sweating changes: the affected area may swell and either sweat excessively or become unusually dry
- Tissue changes: over time, nails may become brittle or ridged, hair growth may increase or decrease, skin may become thin and shiny, and joints can stiffen with reduced range of motion
Weakness, tremor, and involuntary muscle contractions can also develop in the affected limb.
How It’s Diagnosed
Causalgia is diagnosed clinically using what are known as the Budapest Criteria, the current standard adopted by the IASP. There is no single blood test or imaging study that confirms the diagnosis. Instead, clinicians look for a pattern: the patient must report at least one symptom in each of the four categories listed above (sensory, blood flow, swelling/sweating, and tissue/motor changes) and show at least one observable sign in two or more of those categories at the time of evaluation.
For the diagnosis to be classified as CRPS type II rather than type I, there must be evidence of a definite nerve injury. This might come from the patient’s history (a penetrating wound, a surgical complication, a severe crush injury) or from nerve conduction testing. The two types may actually exist on a spectrum rather than as entirely separate conditions, but the distinction matters because the underlying pain mechanism differs. In type I, the pain is driven by tissue damage without nerve injury. In type II, the pain is neuropathic, originating from the damaged nerve itself.
Medication for Pain Management
First-line medications for causalgia target the nervous system rather than the site of injury. Three main drug classes are recommended as initial treatments: anticonvulsants that calm overactive nerve signals (gabapentin, pregabalin), older antidepressants that block pain transmission in the spinal cord (tricyclics like amitriptyline or nortriptyline), and newer antidepressants that boost pain-inhibiting chemicals in the brain and spinal cord (duloxetine, venlafaxine).
These medications are typically started at low doses and increased gradually over weeks. The goal is finding the lowest effective dose that provides meaningful pain relief with tolerable side effects. None of these medications were originally designed for pain, but they work because causalgia is fundamentally a problem of nerve signaling, not tissue inflammation. Standard painkillers like ibuprofen or acetaminophen are generally ineffective for this type of pain.
Rehabilitation and Retraining the Brain
Because causalgia changes how the brain processes signals from the affected limb, physical rehabilitation often focuses on retraining the brain rather than simply exercising the limb. A technique called graded motor imagery breaks this retraining into three progressive stages.
In the first stage, you practice identifying images of left and right body parts on flashcards or a screen. This sounds simple, but people with chronic regional pain often struggle to distinguish their affected side from their unaffected side. Even looking at images of the painful body part can initially trigger discomfort. With repetition, the brain re-establishes its spatial awareness of the limb.
The second stage involves visualization. You imagine performing specific movements, like bending or stretching the affected hand, without actually moving. This activates motor pathways in the brain that may have gone dormant due to pain avoidance, preparing the nervous system for real movement.
The third stage is mirror therapy. You place a mirror between your limbs and perform movements with the unaffected side while watching its reflection. The brain interprets the mirror image as the painful limb moving comfortably. Over time, this creates new associations between movement and comfort rather than movement and pain. As one rehabilitation specialist at the Shirley Ryan AbilityLab put it, when you avoid moving a painful limb, parts of the brain “get dusty.” Graded motor imagery turns those pathways back on.
Spinal Cord Stimulation for Severe Cases
When medications and rehabilitation don’t provide adequate relief, spinal cord stimulation is sometimes considered. This involves implanting a small device that delivers mild electrical pulses to the spinal cord, interrupting pain signals before they reach the brain. Patients typically undergo a trial period with a temporary device before committing to a permanent implant.
Long-term data paints a mixed picture. In one study following patients over a median of eight years, about 54% experienced meaningful benefit from the device. Pain relief typically peaked between 6 and 12 months after implantation, then gradually diminished over time. Roughly 30% of patients who initially had a successful trial eventually had their devices removed, mostly because the pain relief faded. The treatment also did not reduce the need for pain medications. Patients continued using the same or higher amounts of medication after implantation. Still, 70% of patients chose to keep their devices in place over the long follow-up period, suggesting the stimulation provided enough benefit to be worth maintaining even if it didn’t eliminate the need for other treatments.