Complex Regional Pain Syndrome (CRPS)

Quick answer

Complex Regional Pain Syndrome (CRPS) is a chronic pain disorder in which the pain is out of proportion to whatever injury triggered it. It usually develops after an injury — sometimes a minor one — and the pain is often described as burning, deep, and unrelenting. The affected limb develops characteristic changes: swelling, skin color changes, temperature differences, and exquisite sensitivity to touch. The condition is poorly understood, but early recognition and aggressive multidisciplinary treatment offer the best outcomes.

The two types

• CRPS Type 1 — formerly “reflex sympathetic dystrophy (RSD).” No identifiable nerve injury. About 90% of cases.
• CRPS Type 2 — formerly “causalgia.” A specific nerve injury can be identified.

The treatment is broadly similar; the distinction is mostly historical.

How to recognize it

The hallmark is pain that doesn’t fit the injury. A patient who sprained an ankle or had minor foot surgery six weeks ago should be improving. With CRPS, they’re dramatically worse — sometimes unable to tolerate a sock, a sheet brushing the foot, or even air movement.

Typical features:

Pain

• Burning, deep, throbbing quality
• Spontaneous — present even without movement or touch
• Allodynia — light touch (clothing, water, breeze) causes severe pain
• Hyperalgesia — even minor pressure causes disproportionate pain

Skin and tissue changes

• Swelling of the affected foot
• Color changes — red, blue, mottled, or pale
• Temperature differences — warmer or colder than the other foot
• Sweating changes — increased or decreased
• Skin texture changes — shiny, thin, or thickened skin
• Hair and nail changes — increased or decreased growth

Motor changes

• Stiffness
• Weakness
• Tremor
• Reluctance to move the limb
• Eventually, contractures and atrophy if untreated

Pattern

• Symptoms typically start in one location (often where the injury was) and may spread to involve the entire foot or beyond
• Symptoms don’t follow a single nerve distribution — they spread regionally

Why this happens

CRPS isn’t fully understood. Several mechanisms are thought to contribute:

• Peripheral nerve sensitization — local nerves become hyperactive
• Central nervous system changes — the spinal cord and brain amplify pain signals (central sensitization)
• Sympathetic nervous system dysfunction — explains the color and temperature changes
• Inflammatory mediators in tissue
• Genetic and immune factors in some patients

The condition is most often triggered by:

• Fractures — particularly of the wrist, ankle, or foot
• Surgery — even routine procedures
• Sprains and strains
• Casts or immobilization — sometimes from prolonged immobilization itself
• Minor procedures — injections, biopsies, blood draws

There’s no clear way to predict who will develop CRPS after a given injury.

Diagnosis

There’s no single confirmatory test — diagnosis is clinical, using the Budapest Criteria. A patient must have:

1. Continuing pain disproportionate to any inciting event
2. At least one symptom in three of four categories (sensory, vasomotor, sudomotor/edema, motor/trophic)
3. At least one sign at the time of evaluation in two of four categories
4. No other diagnosis that better explains the symptoms

Supporting tests sometimes used:

• Bone scan — may show changes in early CRPS
• MRI — for excluding other diagnoses
• Thermography — documents temperature differences
• Nerve conduction studies — for suspected CRPS Type 2

Treatment

CRPS treatment is multidisciplinary and works best when started early.

Cornerstone: physical and occupational therapy

This is the most important component:

• Desensitization — gradual, progressive exposure to touch, temperature, textures
• Range of motion exercises — preventing stiffness and contracture
• Weight-bearing progression — slowly returning normal use to the limb
• Mirror therapy — using a mirror to “trick” the brain into seeing normal limb movement, reducing pain
• Graded motor imagery — mental practice of movement
• Functional restoration

Avoiding immobilization is critical — the longer the limb is “guarded,” the more entrenched the pain becomes.

Medications

• Neuropathic pain medications — gabapentin, pregabalin, duloxetine, amitriptyline
• NSAIDs for inflammation
• Bisphosphonates — some evidence for early CRPS
• Topical medications — lidocaine patches, capsaicin
• Vitamin C — sometimes used after wrist or foot surgery to reduce CRPS risk
• Opioids — generally limited; not very effective for neuropathic pain and carry their own risks

Interventional treatments

• Sympathetic nerve blocks — local anesthetic blocks of the sympathetic ganglia (lumbar sympathetic block for foot CRPS). Both diagnostic and therapeutic.
• Spinal cord stimulators — for refractory cases
• Dorsal root ganglion stimulators — newer option
• Intrathecal medication pumps — for severe refractory cases
• Ketamine infusions — used in specialty centers

Psychological support

CRPS has a significant psychological burden, and psychological care is part of best-practice treatment:

• Cognitive-behavioral therapy — coping strategies, pain management
• Treatment of associated depression and anxiety — common in chronic pain
• Support groups — RSDSA and similar organizations

Outlook

CRPS outcomes are highly variable. Some patterns:

• Early diagnosis and treatment — best outcomes; many cases resolve or substantially improve within a year
• Delayed treatment — much harder to reverse; may become permanent
• Most patients improve with multidisciplinary care, though “complete cure” is uncommon
• A meaningful minority have persistent symptoms despite treatment

The condition can be life-altering, and matching the patient with experienced multidisciplinary care is critical.

Bottom line

CRPS is the diagnosis that should be considered when a foot injury — even a minor one — causes pain dramatically out of proportion to the injury, with skin changes, swelling, and exquisite sensitivity. Early, aggressive multidisciplinary treatment — anchored in physical therapy and including medications, blocks, and psychological support — gives the best chance of recovery. Time matters: the longer CRPS persists, the harder it is to reverse, so early referral to a pain specialist is one of the most important steps.