Complex Regional Pain Syndrome (CRPS)

Complex Regional Pain Syndrome (CRPS) is a chronic pain condition that typically develops after trauma or surgery, characterized by disproportionate pain, vasomotor changes, and trophic changes. Formerly known as Reflex Sympathetic Dystrophy (RSD) or Sudeck's atrophy.

Historical context:

• First described by Silas Weir Mitchell in 1864 (causalgia)
• Sudeck described atrophy in 1900
• Reflex Sympathetic Dystrophy term used until 1994
• CRPS term adopted in 1994 (IASP)
• Budapest criteria established in 2003 (current diagnostic standard)

Epidemiology (verified, population-based):

• Population incidence: 5-26 per 100,000 person-years (Olmsted County vs Dutch primary-care data — estimates vary several-fold with case-finding method)
• Female:Male ratio: 3-4:1; highest incidence in postmenopausal women (61-70 years)
• Median onset age ~46 years; upper limb affected more often than lower limb
• Commonest trigger: fracture (44-46%), especially distal radius; also surgery, sprains, spontaneous onset
• After distal radius fracture, untreated CRPS occurred in ~10% of placebo patients in the Zollinger RCT
• Risk factors: female sex, fracture/immobilisation, cast-related complaints, possibly anxiety/depression
• Around 74% of CRPS-I cases resolve, often spontaneously (Olmsted County data)

Pathophysiology: The exact mechanism is unclear, but multiple theories exist:

Key Pathophysiological Concepts:

• Allodynia: Pain from non-painful stimuli (light touch) - indicates central sensitization
• Hyperalgesia: Exaggerated pain from painful stimuli - indicates peripheral and central sensitization
• Vasomotor changes: Temperature/color asymmetry - indicates autonomic dysfunction
• Trophic changes: Hair loss, nail changes, skin atrophy - indicates chronic changes

Stages of CRPS:

Stage 1 (Acute, 0-3 months):

• Pain, swelling, warmth, erythema
• Limited ROM
• Hyperalgesia, allodynia
• Best prognosis with treatment

Stage 2 (Dystrophic, 3-6 months):

• Progression of trophic changes
• Skin becomes cool and clammy
• Hair loss, nail brittleness
• Muscle atrophy begins
• Treatment still helps but prognosis moderate

Stage 3 (Atrophic, over 6 months):

• Irreversible changes
• Severe atrophy, contractures
• Severe pain, functional disability
• Poor prognosis - permanent disability

View larger

History:

• Recent trauma or surgery (weeks to months)
• Pain out of proportion to injury
• Progressive symptoms
• Previous CRPS (10-30% recurrence risk)
• Female, smoking, anxiety/depression (risk factors)

Physical Examination:

Key Clinical Signs:

• Allodynia: Light touch causes pain - pathognomonic
• Temperature asymmetry: Measure with thermometer - greater than 1°C difference
• Color changes: Blotchy, purple, red, or pale appearance
• Trophic changes: Hair loss, nail brittleness, skin atrophy (late finding)

Clinical Diagnosis:

• CRPS is primarily a clinical diagnosis
• Budapest criteria are diagnostic
• No definitive test confirms CRPS
• Tests are supportive, not diagnostic

Supportive Investigations:

Three-Phase Bone Scan:

• Phase 1 (blood flow): Increased perfusion
• Phase 2 (blood pool): Increased pooling
• Phase 3 (delayed): Increased uptake in affected limb
• Sensitivity: 50-80% (normal scan doesn't exclude CRPS)
• Specificity: Moderate

MRI:

• Patchy bone marrow edema
• Soft tissue edema
• Not diagnostic but supportive
• May help exclude other diagnoses

Note: CRPS itself is not a surgical condition, but surgical procedures may be needed for the underlying injury. This section addresses surgical considerations when CRPS is present or at risk.

Chronic CRPS:

• 10-20% develop chronic CRPS with permanent disability
• Poor prognosis if treatment delayed
• May require long-term pain management
• Functional impairment may be permanent

Contractures:

• Late complication (Stage 3)
• May require surgical release
• Prevention through early treatment is key
• Physiotherapy essential

After Surgery (CRPS Prevention):

If CRPS Develops:

• Immediate multidisciplinary referral
• Physiotherapy (cornerstone)
• Medications (gabapentin first-line)
• Sympathetic blocks if needed
• Psychological support
• Pain clinic referral

What the evidence actually shows:

• In the Olmsted County population study, ~74% of CRPS-I cases resolved, often spontaneously (Sandroni 2003)
• A minority develop persistent, disabling chronic CRPS; outcomes are heterogeneous and hard to predict
• Beware quoting precise stage-based recovery percentages: the three-stage model is not validated

Factors associated with worse outcome (clinical, not precisely quantified):

• Longer symptom duration and delayed recognition
• The "cold"/central CRPS phenotype
• Marked motor/trophic changes and established contractures
• Psychological distress (anxiety/depression) as a comorbidity
• Previous CRPS (recurrence risk)

CRPS is a clinical diagnosis of exclusion (Budapest criterion 4: no other diagnosis better explains the findings). The key mimics after limb trauma or surgery must be actively excluded before labelling a patient with CRPS.

CRPS is one of the most contested diagnoses in orthopaedics. High-yield areas of genuine uncertainty:

Global epidemiology:

• Population incidence varies several-fold by case-finding: 5.5 per 100,000 person-years (Olmsted County, USA) to 26.2 per 100,000 (Dutch primary care)
• Consistently female-predominant (3-4:1), peaking in postmenopausal women; fracture is the commonest trigger worldwide (44-46%)
• The diagnosis is clinical and standardised internationally by the Budapest criteria, so cross-country comparison is more consistent than for many pain conditions

Side-by-side guideline comparison:

Registry and surgical-practice notes:

• CRPS is not tracked in joint registries, but registry-level evidence informs prevention: minimising re-operation, immobilisation and repeated cast complaints reduces risk
• Spinal cord stimulation outcomes are followed in device/pain registries; real-world data echo the trial finding of pain (not function) benefit with a meaningful revision rate

High- vs limited-resource practice variation:

• High-resource settings: ready access to multidisciplinary pain services, graded motor imagery programmes, interventional blocks and SCS
• Limited-resource settings: emphasis shifts to early recognition, low-cost interventions (active rehabilitation, simple analgesics, amitriptyline, vitamin C prophylaxis after wrist fracture) and avoidance of prolonged immobilisation, since advanced interventional and neuromodulation options may be unavailable