How we recognize it

The diagnosis is clinical, made at the bedside against a set of signs called the Budapest criteria, and it does not require an MRI because there is no scan that shows CRPS. In plain terms: the pain has to be out of proportion to whatever started it, and the limb has to show evidence in at least three of four categories — temperature or color change compared with the other side, swelling or sweating that is not symmetric, a change in hair, nail or skin texture, and a change in motor function or strength. At least two of those categories have to be present on our exam the day we see you, not just in the history. That distinction is what keeps the diagnosis from being handed out to every patient whose pain simply outlasted its injury.

The mechanism, and why it is never only nerve

Two biological drivers converge here. The first is a sympathetic and inflammatory storm at the injury site — small nerve fibers that regulate blood flow and sweating start firing abnormally, and inflammatory cytokines keep the tissue behaving like it is still being injured. The second is central: the spinal cord and somatosensory cortex remap the limb, widening its receptive field so a light touch or a cool breeze registers as an assault. Neither explains the whole picture. The third driver is what we watch happen more than any lab value: a patient who is not believed loses sleep, loses movement, and loses the social support that would otherwise buffer a nervous system already primed to escalate. Isolation and disbelief are not side effects of CRPS — they are inputs into it.

What starts it

Most cases follow a specific, identifiable event: a wrist or ankle fracture, a sprain that never quite settled, a surgery on a hand or foot, or a car accident with no fracture on the images. The common thread is not severity — some of the worst CRPS we manage followed injuries that looked minor on the day. What predicts it is what the nervous system does next, and that is largely outside the patient’s control.

What it is not

A red, swollen limb is also consistent with a deep vein thrombosis, an infection, a missed compartment syndrome, or ordinary post-surgical inflammation that simply takes longer than expected. We rule those out first, because treating CRPS in a limb that actually has a clot delays the treatment that limb needs. Peripheral neuropathy can also mimic the burning and color change without the sympathetic signature.

How we diagnose it here

Beyond the bedside exam, a diagnostic sympathetic nerve block does double duty. If anesthetizing the sympathetic chain to the limb produces meaningful relief, that confirms the sympathetic nervous system is driving part of the pain, and the block itself becomes therapeutic, not just diagnostic. If it does not help, that points us toward a more centrally driven pattern and changes what we reach for next.

Interventional options, matched to what is actually driving it

The terrain underneath it

A nervous system running on poor sleep, chronic stress hormones and metabolic inflammation has a lower threshold for exactly the kind of central sensitization CRPS depends on. We do not treat CRPS as a pure orthopedic accident. Sleep, graded movement, and the in-house behavioral work our clinic delivers — Acceptance and Commitment Therapy with a licensed, pain-trained clinician, never a referral out — address the nervous system’s threat state directly, and together they are roughly 40 to 50 percent of a CRPS plan alongside the procedures. See sleep, movement and behavior.

Where surgery fits

Surgery is not part of the initial treatment plan for CRPS, and an elective operation on an actively flaring limb can provoke a new flare at a fresh surgical site. The exception is the implant itself — a spinal cord stimulator or, less commonly, an intrathecal pump — a minor procedure we perform once a trial has proven it works.

The belief problem

Because there is no blood test and no scan, patients with CRPS are routinely told their pain is psychological, that they are exaggerating, or that they should be further along by now. That disbelief is not a footnote — it is one of the three drivers above, and it is often what delays a patient reaching treatment until the window when it works best has already narrowed. If you have been told your limb “looks fine” while it burns, you are describing a real, diagnosable condition.

Red flags that change the visit

• A hot, swollen limb with fever — needs same-day evaluation for infection, not a CRPS workup first.
• Sudden calf swelling and pain, especially after a cast or a long period of immobility — rule out a blood clot before anything else.
• Rapidly worsening pain in a recently casted or wrapped limb — compartment syndrome is a surgical emergency, not a pain-clinic visit.
• New weakness or numbness spreading beyond the injury site — warrants urgent evaluation. See when it is an emergency.

Common questions

Related reading

• Sympathetic nerve blocks
• Ketamine for CRPS
• Spinal cord stimulation
• After a car accident
• Peripheral neuropathy