COMPLEX REGIONAL PAIN SYNDROME (CRPS)

MPT Topper-Level Answer for MUHS Examination

QUESTION 1 & 2 (30 Marks): Pathophysiology, Evidence-Based Assessment, Management following Distal End Radius Fracture + Rehabilitation

DEFINITION AND CLASSIFICATION

• Reflex Sympathetic Dystrophy (RSD) - Evans, 1946
• Causalgia - Weir Mitchell, 1870s
• Sudeck's Atrophy, Shoulder-Hand Syndrome, Algodystrophy
• Modern term: CRPS - introduced by IASP, 1994

• CRPS Type I (= RSD): No identifiable nerve lesion; accounts for ~90% cases
• CRPS Type II (= Causalgia): Identifiable peripheral nerve lesion present

• Mean age: 36-46 years; female predominance (60%-81%)
• Precipitated by: fracture (16-46%), strain/sprain (10-29%), post-surgical (3-24%), contusion/crush (8-18%)
• Incidence after distal radius fracture: 0.19% - 13.63% (Meta-analysis, Lorente et al., 2023, PMID 37209231)

SECTION A: PATHOPHYSIOLOGY OF CRPS

1. PERIPHERAL SENSITIZATION

• Substance P, Calcitonin Gene-Related Peptide (CGRP), bradykinin, histamine, prostaglandins
• These promote neurogenic inflammation - characterized by vasodilation, plasma extravasation, and edema
• Sustained peripheral input leads to sensitization of primary afferent C and A-delta fibers
• This accounts for the hallmark features: hyperalgesia and allodynia

2. CENTRAL SENSITIZATION

• Wind-up phenomenon in dorsal horn neurons (WDR neurons become hyperexcitable)
• NMDA receptor activation and increased intracellular calcium
• Long-term potentiation (LTP) in pain pathways
• Loss of descending inhibition (reduced serotonin-norepinephrine modulation)
• Results in: allodynia, hyperalgesia, hyperpathia - pain spreading beyond the original injury zone

3. SYMPATHO-AFFERENT COUPLING (Sympathetically Maintained Pain - SMP)

• In normal physiology, sympathetic efferents and sensory afferents do not cross-communicate
• After nerve/tissue injury, alpha-adrenoreceptors are upregulated on nociceptors
• Norepinephrine released by sympathetic terminals directly activates these receptors
• This creates an abnormal reflex arc that perpetuates pain
• Clinically explains why sympathetic blocks provide pain relief
• IMPORTANT: Current understanding shows decreased sympathetic outflow to the affected limb, with autonomic features now attributed to catecholamine hypersensitivity at peripheral receptors - not sympathetic overactivity (Bradley & Daroff's Neurology, 8th Ed.)

4. NEUROINFLAMMATION AND IMMUNE DYSREGULATION

• Elevated pro-inflammatory cytokines: TNF-alpha, IL-1beta, IL-6 in affected tissue
• Mast cell degranulation and activation of complement cascade
• Autoimmune theory: autoantibodies against beta-2 adrenergic receptors and muscarinic receptors detected in some CRPS patients
• Neurogenic inflammation involves antidromic release of neuropeptides (Substance P, CGRP) causing plasma protein extravasation and vasodilatation
• This accounts for the warmth, erythema, and edema in early CRPS

5. CORTICAL REORGANIZATION AND CENTRAL NERVOUS SYSTEM CHANGES

• Somatosensory cortex reorganization: shrinkage of cortical representation of the affected limb (demonstrated on fMRI/MEG)
• The magnitude of cortical reorganization correlates directly with pain intensity
• Glial activation: microglia and astrocytes in spinal cord contribute to central sensitization
• Motor cortex changes: impaired voluntary movement, dystonia, tremor
• Psychological factors (catastrophizing, fear-avoidance, anxiety, depression) amplify cortical processing of pain signals

6. VASCULAR/AUTONOMIC DYSFUNCTION

• Phase-dependent vasomotor changes:
  • Acute/warm phase: Vasodilation - skin is warm, red, with increased sweating
  • Chronic/cold phase: Vasoconstriction - skin becomes cold, cyanotic, mottled
• Mechanism: Decreased sympathetic outflow + upregulated peripheral adrenergic receptors
• Livedo reticularis: non-blanchable red reticulated skin pattern (~60% of CRPS patients)

7. OXIDATIVE STRESS MECHANISM

• Free radicals (reactive oxygen species) accumulate in injured tissue
• Antioxidant defense is overwhelmed
• This mechanism provides rationale for Vitamin C prophylaxis (500 mg/day for 50 days post-fracture reduces CRPS risk by ~70%, Zollinger et al.)
• Ferraro et al., Lancet Neurology 2024 (PMID 38631768): CRPS classified as a chronic primary pain disorder with complex interacting biological, psychological, and social mechanisms

PATHOPHYSIOLOGY DIAGRAM (Conceptual):

TRAUMA (DER Fracture)
        ↓
Peripheral Tissue/Nerve Injury
        ↓
Neurogenic Inflammation (Substance P, CGRP, Bradykinin)
        ↓                                    ↓
Peripheral Sensitization          Sympatho-Afferent Coupling
(C-fiber upregulation)           (α-adrenoreceptor expression)
        ↓                                    ↓
Central Sensitization ←————— Perpetuated Nociceptive Drive
(NMDA, Wind-up, LTP)
        ↓
Cortical Reorganization
(Shrinkage of somatosensory map)
        ↓
        ↓
CRPS Clinical Manifestations:
Pain + Allodynia + Autonomic Changes + Motor/Trophic Changes

CLINICAL FEATURES - THREE STAGE PROGRESSION

SECTION B: ASSESSMENT / DIAGNOSIS

BUDAPEST DIAGNOSTIC CRITERIA (IASP Revised, Validated 2010 - Harden et al.)

• Sensory: Hyperesthesia, allodynia
• Vasomotor: Temperature asymmetry, skin color changes
• Sudomotor/Edema: Edema, sweating changes
• Motor/Trophic: Decreased ROM, motor dysfunction (weakness, tremor, dystonia), trophic changes (hair, nails, skin)

• Sensory: Hyperalgesia to pinprick, allodynia to light touch
• Vasomotor: Evidence of temperature asymmetry (>1°C), skin color changes
• Sudomotor/Edema: Edema, sweating changes
• Motor/Trophic: Decreased ROM, motor dysfunction, trophic changes

ASSESSMENT TOOLS FOR MPT PRACTICE

INVESTIGATIONS

• Plain X-ray: Periarticular osteoporosis ("Sudeck's atrophy"), soft tissue swelling
• Triple-phase bone scan (Tc-99m): Increased uptake in delayed phase in early CRPS (sensitivity 60%, specificity 86%)
• MRI: Excludes other pathologies; may show bone marrow edema
• Thermography: Documents temperature asymmetry
• EMG/NCS: Differentiates CRPS Type I from Type II

RISK FACTORS FOR CRPS AFTER DISTAL RADIUS FRACTURE

• Female sex (RR 1.20; 95% CI: 1.05-1.37)
• High BMI (MD: 1.17; 95% CI: 0.45-1.88)
• Open fractures and high-energy mechanisms (RR 0.18 for low-energy)
• Associated ulnar fracture (RR: 1.25; 95% CI: 1.17-1.35)
• Psychiatric comorbidity (RR: 2.04; 95% CI: 1.83-2.28) - strongest risk factor
• Type of surgery (ORIF vs. external fixation) was NOT a risk factor

SECTION C: EVIDENCE-BASED MANAGEMENT

MANAGEMENT FRAMEWORK: Multidisciplinary Approach

1. PHYSIOTHERAPY (CORNERSTONE OF TREATMENT)

Phase 1: Acute Stage Physiotherapy

• Edema control: Elevation, gentle retrograde massage, contrast baths (alternating warm 40°C / cold 15°C), compression garments
• Pain relief: TENS (high-frequency, conventional mode over peripheral nerve territory), interferential therapy
• Gentle active ROM: Within pain-free range; avoid aggressive passive stretching
• Desensitization: Graded sensory re-education - starting with coarse textures, progressing to fine

Phase 2: Sub-Acute / Active Rehabilitation

• Graded Motor Imagery (GMI) Protocol (Moseley, 2004-2006):
  1. Limb laterality recognition - 2 weeks: visual recognition of left/right limb images
  2. Imagined movements - 2 weeks: mental imagery of movements without actually moving
  3. Mirror Therapy - 2 weeks: mirror box - visual feedback of unaffected limb creates illusion of normal movement
  • Mechanism: Gradually desensitizes the cortical representation and reverses cortical reorganization
  • Evidence: Low-to-moderate quality evidence for functional improvement (Cochrane Review, Smart et al., 2022, PMID 35579382)
• Graded Exposure / Pain Exposure Physical Therapy (PEPT):
  • Progressive loading despite pain ("pain is not always dangerous")
  • Patients are educated that pain ≠ tissue damage
  • Addresses catastrophizing and fear-avoidance behaviors
  • Rockwood & Green (2025) describes a case of complete CRPS resolution with PEPT within 3 months
• Proprioceptive retraining: Wrist proprioception exercises, wobble board for upper limb
• Strengthening: Gradual progressive resistance of wrist flexors/extensors, grip

Phase 3: Functional Restoration

• Work hardening / task-specific training: Simulated ADL tasks
• Aerobic conditioning: Gradually increasing aerobic activities - gold standard for long-term CRPS management
• Hydrotherapy: Warm water reduces sympathetic tone and facilitates movement

TENS Parameters for CRPS:

• Conventional TENS: 80-100 Hz, 50-100 μs, comfortable tingling sensation
• Acupuncture-like TENS: 1-4 Hz, 200-250 μs - for endorphin release
• Applied to nerve territory proximal to painful area

2. OCCUPATIONAL THERAPY

• Splinting: Resting splints for pain relief; dynamic splints for contracture prevention
• Functional retraining for ADLs: writing, dressing, grip activities
• Ergonomic modification and work adaptation

3. PSYCHOLOGICAL INTERVENTIONS

• Cognitive Behavioral Therapy (CBT): Targets pain catastrophizing, kinesiophobia (fear of movement), depression and anxiety
• Acceptance and Commitment Therapy (ACT): Helps patient resume limb use despite pain
• Pain education: Graded understanding that pain ≠ tissue damage
• Psychotherapy goals: Improve QOL, develop coping skills, combat stress and despair
• Psychiatric comorbidity is the strongest risk factor (RR 2.04); psychological treatment is mandatory (Rheumatology, 2-Volume Set, 2022, Elsevier)

4. PHARMACOLOGICAL MANAGEMENT

5. INTERVENTIONAL / MINIMALLY INVASIVE PROCEDURES

• Stellate ganglion block: Sympathetic block in upper limb CRPS; most effective in early stages; may prevent recurrence during reoperation
• Intravenous Regional Block (Bier Block): Guanethidine or Bretylium; longer analgesia than lidocaine
• Epidural analgesia: Clonidine + Ketamine epidural
• Intrathecal drug delivery: Baclofen (for dystonia/spasm) + Morphine
• Lumbar/thoracic sympathectomy: Surgical or chemical; for refractory lower/upper limb CRPS

6. NEUROMODULATION

• Spinal Cord Stimulation (SCS):
  • Implanted electrode at dorsal column level
  • Mechanism: Gate control theory; activates descending inhibitory pathways
  • Early studies: Long-term pain reduction and improved QOL
  • Kemler et al. (2008, 5-year follow-up): No extra benefit of SCS + PT over PT alone in long-term
  • Indication: Refractory CRPS not responding to conservative management
  • (Bradley & Daroff's Neurology in Clinical Practice)
• Transcranial Magnetic Stimulation (TMS): Emerging - targets motor cortex reorganization

SECTION D: SPECIFIC CONSIDERATIONS - POST DISTAL END RADIUS FRACTURE

Prevention Protocol (Evidence-Based):

1. Vitamin C 500 mg/day for 50 days post-fracture (Level I evidence - Zollinger et al.)
2. Avoid excessive cast tightness
3. Early mobilization of uninvolved joints (fingers, elbow, shoulder)
4. Educate patient about CRPS risk and early warning signs

Rehabilitation Protocol Timeline (Post DER Fracture):

If CRPS Develops Post-DER Fracture:

• Early detection (Stage I) gives best prognosis
• Use Budapest criteria to confirm diagnosis
• Immediate multidisciplinary referral: pain physician + physiotherapist + psychologist
• Start GMI protocol + desensitization
• Pharmacological adjuncts (Gabapentin, Vitamin C continued, corticosteroids if warm phase)
• Goal: maintain limb use, prevent progression to Stage III

QUESTION 3 (10 Marks): Mechanism of CRPS and Management Guidelines

MECHANISM (Summary):

1. Peripheral Sensitization: Post-traumatic neurogenic inflammation (Substance P, CGRP, bradykinin) sensitizes primary nociceptors. Reduced threshold for activation = allodynia and hyperalgesia.
2. Central Sensitization: Wind-up phenomenon, NMDA receptor-mediated LTP in dorsal horn. Pain spreads beyond original injury zone. Loss of descending inhibition.
3. Sympatho-Afferent Coupling: Alpha-adrenoreceptor upregulation on nociceptors. Sympathetic activity directly activates pain fibers. Basis of sympathetically-maintained pain (SMP).
4. Neuroinflammation + Immune Dysregulation: Pro-inflammatory cytokines (TNF-alpha, IL-1β, IL-6), mast cell activation, possible autoantibodies. Sustained tissue inflammation.
5. Cortical Reorganization: Shrinkage of somatosensory cortical representation of affected limb. Magnitude correlates with pain. Impaired cortical motor control.

MANAGEMENT GUIDELINES (Algorithm):

CRPS DIAGNOSED (Budapest Criteria)
              ↓
         STAGE ASSESSMENT
              ↓
    ┌─────────┬───────────┐
  Stage I   Stage II   Stage III
 (Warm)   (Dystrophic) (Atrophic)
    ↓          ↓          ↓
All stages: MULTIDISCIPLINARY TEAM APPROACH
              ↓
┌─────────────────────────────────────────────┐
│  1. PHYSIOTHERAPY (CORNERSTONE)             │
│     - Edema control, desensitization        │
│     - Graded Motor Imagery + Mirror Therapy │
│     - PEPT (Pain Exposure Physical Therapy) │
│     - Aerobic conditioning                  │
├─────────────────────────────────────────────┤
│  2. PSYCHOLOGICAL THERAPY                   │
│     - CBT, pain education, ACT              │
├─────────────────────────────────────────────┤
│  3. PHARMACOTHERAPY                         │
│     - Neuropathic agents (Gabapentin)       │
│     - Corticosteroids (acute/warm phase)    │
│     - Bisphosphonates, Calcitonin           │
│     - Vitamin C (prophylaxis)               │
├─────────────────────────────────────────────┤
│  4. INTERVENTIONAL (if inadequate response) │
│     - Stellate ganglion block               │
│     - IVRB (Bier block)                     │
│     - Epidural/Intrathecal delivery         │
├─────────────────────────────────────────────┤
│  5. NEUROMODULATION (refractory cases)      │
│     - Spinal Cord Stimulation (SCS)         │
│     - rTMS (emerging)                       │
└─────────────────────────────────────────────┘

RECENT ADVANCES (2022-2025)

1. CRPS as Chronic Primary Pain (ICD-11): Ferraro et al., Lancet Neurology 2024 (PMID 38631768): CRPS reclassified as chronic primary pain disorder reflecting its biopsychosocial origin, not purely sympathetic or neurological.
2. Autoimmune Hypothesis: Evidence of autoantibodies against beta-2 adrenergic and muscarinic M2 receptors; trials of IVIG (IV immunoglobulin) in seronegative refractory CRPS showing promise.
3. Graded Motor Imagery (GMI): Cochrane Review 2022 (Smart et al., PMID 35579382): Low-but-promising evidence for GMI and mirror therapy; large RCTs underway.
4. Risk Stratification Post-DRF: Meta-analysis 2023 (Lorente et al., PMID 37209231): Psychiatric disorders carry highest risk (RR 2.04). Routine pre-operative psychological screening recommended.
5. Ketamine Infusion Protocol: Subanesthetic IV ketamine (0.1-0.5 mg/kg/hr) for refractory CRPS - consensus protocol published (Xu et al., Pain Med, 2019).
6. Neuromodulation: High-frequency SCS (10 kHz, burst SCS) showing superior outcomes over traditional SCS in emerging studies.
7. Vitamin C Evidence Update: 500 mg/day prophylaxis remains guideline standard; ongoing research into optimal dosing and duration.

BOOK REFERENCES

1. Bradley and Daroff's Neurology in Clinical Practice, 8th Edition (Elsevier, 2022) - Chapter 52: Complex Regional Pain Syndrome
2. Campbell's Operative Orthopaedics, 15th Edition (2026) - Chapter on CRPS
3. Rockwood and Green's Fractures in Adults, 10th Edition (2025) - Chapter 27: CRPS after fractures
4. Rheumatology, 2-Volume Set (Elsevier, 2022) - Chapter 87: CRPS
5. Harrison's Principles of Internal Medicine, 22nd Edition (McGraw-Hill, 2025)
6. Barash, Cullen and Stoelting's Clinical Anesthesia, 9th Edition - CRPS and Sympathetic blocks
7. Ferraro MC et al. Complex regional pain syndrome: advances in epidemiology, pathophysiology, diagnosis, and treatment. Lancet Neurol. 2024 May. [PMID: 38631768]
8. Lorente A et al. Incidence and risk factors for complex regional pain syndrome in radius fractures: meta-analysis. Arch Orthop Trauma Surg. 2023. [PMID: 37209231]
9. Smart KM et al. Physiotherapy for pain and disability in adults with CRPS types I and II. Cochrane Database Syst Rev. 2022. [PMID: 35579382]

Examiner's Tip for 30M Answer: Always include the Budapest Criteria table, a pathophysiology mechanism diagram/flowchart, the three-stage clinical table, and a structured management algorithm. Mention the multidisciplinary approach explicitly. For DER fracture specifically: add Vitamin C prophylaxis, risk factors table, and a phased rehabilitation timeline. For 10M: focus on 5 core mechanisms + management algorithm only.