Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) is a debilitating chronic pain condition that typically affects a single extremity following trauma, surgery, fracture, or a period of immobilisation. The hallmark of CRPS is pain that is grossly disproportionate to the severity of the initial inciting event, accompanied by a constellation of sensory, vasomotor, sudomotor, motor, and trophic disturbances that evolve over time. The condition was historically termed reflex sympathetic dystrophy (CRPS Type I) or causalgia (CRPS Type II) and was formally reclassified by the International Association for the Study of Pain (IASP) in 1994, with diagnostic refinements through the Budapest Criteria consensus process in 2003.

CRPS is divided into two subtypes:

• CRPS Type I — occurs without a confirmed nerve injury (approximately 90% of cases). Commonly follows distal radius fractures, ankle sprains, crush injuries, or surgical procedures including carpal tunnel release and total knee arthroplasty.
• CRPS Type II — occurs with an identifiable major nerve lesion (approximately 10% of cases). May follow peripheral nerve laceration, traction injury, or iatrogenic nerve damage during surgery.

Australian Epidemiology

Population-based data from the Netherlands and other Western nations estimate CRPS incidence at approximately 26 per 100,000 person-years. Australian-specific incidence data are limited, but extrapolation from comparable healthcare systems suggests 5,000–7,000 new cases per year nationally. The condition is 3–4 times more common in women than men, with peak incidence between ages 50 and 70 years. Paediatric CRPS is increasingly recognised in Australian tertiary paediatric centres, with a mean age of onset of 10–12 years and a strong female predominance (4:1).

In Australia, the economic burden is substantial: affected individuals frequently require extended time away from work, multiple specialist consultations, allied health interventions, and sometimes invasive procedures. The Australian Institute of Health and Welfare (AIHW) recognises chronic pain conditions including CRPS as significant contributors to disability-adjusted life years (DALYs) and reduced workforce participation.

The Budapest Criteria (revised 2010) are the internationally accepted diagnostic standard for CRPS, adopted by the IASP and validated in multiple cohorts including Australian pain medicine practice. They replaced the original 1994 IASP criteria, which had high sensitivity (0.98) but poor specificity (0.36). The revised criteria improve specificity (0.68–0.79) while maintaining good sensitivity (0.85–0.99).

Clinical Budapest Diagnostic Criteria

A diagnosis of CRPS requires all four of the following:

1. Continuing pain that is disproportionate to any inciting event.
2. The patient reports at least one symptom in three of the four following categories.
3. The clinician displays at least one sign in two or more of the following categories on examination.
4. No other diagnosis can better explain the signs and symptoms.

Budapest Research Criteria

For research purposes, stricter criteria apply: the patient must report at least one symptom in all four categories and display at least one sign in two or more categories on examination. This reduces sensitivity but increases specificity and is used in clinical trials conducted at Australian pain research centres.

The pathophysiology of CRPS is complex and multifactorial, involving peripheral and central nervous system changes, inflammation, and autonomic dysfunction. No single mechanism fully accounts for the clinical picture, and multiple pathways likely coexist and interact at different disease stages.

Peripheral Mechanisms

• Neurogenic inflammation: Tissue injury triggers release of substance P and calcitonin gene-related peptide (CGRP) from C-fibre nociceptors, leading to vasodilation, oedema, and protein extravasation (plasma extravasation). This accounts for the early inflammatory features — warmth, swelling, and erythema.
• Sympathetic-afferent coupling: Following nerve injury, noradrenaline released from sympathetic efferent neurons can activate α-adrenergic receptors expressed on sensitised nociceptors. This mechanism contributes to sympathetically maintained pain (SMP), which may respond to sympathetic blockade.
• Peripheral sensitisation: Inflammatory mediators (prostaglandins, bradykinin, nerve growth factor) lower activation thresholds of peripheral nociceptors, amplifying pain signalling to the spinal cord.

Central Mechanisms

• Central sensitisation: Sustained nociceptive input leads to increased excitability of dorsal horn neurons, expansion of receptive fields, and recruitment of Aβ-fibres into pain pathways. This underlies the development of allodynia and hyperalgesia.
• Cortical reorganisation: Functional MRI studies demonstrate blurred representation of the affected limb in the somatosensory cortex (S1), reduced cortical thickness, and disrupted body schema. This cortical smudging correlates with the magnitude of pain and motor dysfunction and is a target for graded motor imagery and mirror therapy.
• Disrupted descending inhibition: Deficiency of descending noradrenergic and serotonergic inhibitory pathways from the brainstem (periaqueductal grey, rostroventral medulla) reduces endogenous pain modulation.

Inflammatory & Immune Mechanisms

• Pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) are elevated in the affected limb and systemically in early CRPS.
• Autoimmune components: antibodies against autonomic nervous system receptors (β2-adrenergic and muscarinic-2 receptors) have been identified in a subset of patients, providing a rationale for IV immunoglobulin (IVIG) therapy.
• Genetic predisposition: HLA associations (HLA-B62, HLA-DQ8) and polymorphisms in TNF-α and IL-1 receptor antagonist genes suggest genetic susceptibility in some populations.

Temporal Phases (Traditional Model)

The traditional triphasic model (acute, dystrophic, atrophic) is now considered an oversimplification, as phases overlap and not all patients progress sequentially. However, it remains a useful clinical framework:

Typical Clinical Features

CRPS most commonly affects the distal extremity — hand/wrist and foot/ankle — though proximal spread and rarely truncal CRPS are recognised. The upper limb is affected more commonly than the lower limb (approximately 60:40 ratio). Key clinical features include:

• Pain: Continuous, burning, throbbing, or aching pain that is disproportionate to the initial injury. Often described as "deep bone pain" or "burning from the inside out." Allodynia (pain to light touch, clothing, or gentle breeze) and hyperalgesia (exaggerated pain response to pinprick) are characteristic.
• Sensory changes: Hyperaesthesia, dysaesthesia, and spatial sensory discrimination deficits. Patients may experience a sensation of the limb feeling "foreign," "swollen," or "not belonging to them" (neglect-like symptoms).
• Vasomotor changes: Temperature asymmetry (usually cooler in chronic CRPS), skin colour changes (erythema, cyanosis, mottling, livedo reticularis pattern), and visible asymmetry compared to the contralateral limb.
• Sudomotor changes: Hyperhidrosis (excessive sweating) of the affected limb, oedema (initially pitting, later brawny and firm).
• Motor dysfunction: Weakness, tremor (often irregular and task-specific), reduced grip strength, involuntary movements including myoclonus and fixed dystonia (particularly in chronic CRPS). Active and passive range of motion is reduced due to pain and capsular thickening.
• Trophic changes: Altered nail growth (ridged, brittle, discoloured), skin atrophy (thin, shiny, cracked), hair changes (initially increased then decreased growth), subcutaneous tissue wasting, and joint stiffness.

Pattern of Spread

CRPS may remain localised or spread in a non-dermatomal pattern to involve the entire ipsilateral limb. Contralateral limb involvement occurs in 7–15% of cases. Spread may occur through mirror-image sympathetic mechanisms or through central sensitisation. Unlike neuropathic dermatomal pain, CRPS spread does not follow nerve root or peripheral nerve territories.

Differential Diagnosis

There is no single confirmatory test for CRPS. Investigations serve two purposes: (1) supporting the clinical diagnosis and (2) excluding other conditions. The following are relevant in the Australian context, with availability and MBS item considerations.

Early identification of patients at high risk for developing CRPS — and early stratification of those with established CRPS into prognostic categories — enables targeted intervention and appropriate resource allocation.

Risk Factors for CRPS Development

Prognostic Factors in Established CRPS

Graded Motor Imagery (GMI)

GMI is a three-stage rehabilitation programme with Level I evidence (systematic review, RCT) for CRPS. It was developed by Lorimer Moseley and colleagues at the University of South Australia and is now used internationally. The three sequential stages are:

Physiotherapy Approach

• Desensitisation: Graded exposure to textures on the affected area (cotton → silk → towelling → Velcro). Reduces allodynia by engaging Aβ-fibre activation and promoting cortical remapping.
• Graded exposure to movement: Start with gentle active range of motion, progress to functional tasks. Pain during rehabilitation is acceptable if it returns to baseline within 24 hours ("traffic light" approach: green = pain settles within 2 hours; amber = within 24 hours; red = persisting beyond 24 hours — reduce intensity).
• Weight-bearing and proprioceptive training: Balance board, wobble cushion exercises for lower limb CRPS. Progressive loading to counteract disuse osteopaenia.
• Hydrotherapy: Warm water (34–36°C) facilitates movement through buoyancy, warmth, and reduced allodynia. Available at many Australian community physiotherapy centres and rehabilitation units.
• Constraint-induced movement therapy (CIMT): Emerging evidence for CRPS patients with significant motor neglect-like dysfunction. Limited availability in Australian settings.

Occupational Therapy

Occupational therapy focuses on functional restoration, return to activities of daily living (ADLs), workplace modification, and ergonomic assessment. Key components include:

• Gradual reintroduction of self-care tasks (dressing, cooking, writing).
• Splinting — only for functional support, not immobilisation. Dynamic splints preferred over static to prevent contracture.
• Workplace assessment and graded return-to-work programme. In Australia, this is typically coordinated through WorkCover/return-to-work insurers and the patient's employer.
• Adaptive equipment for persistent functional impairment (e.g., built-up handles, jar openers).

Pharmacotherapy for CRPS targets multiple pathophysiological mechanisms and should be used as an adjunct to rehabilitation — not as standalone therapy. Treatment is individualised based on the predominant symptom complex (nociceptive vs. neuropathic vs. inflammatory vs. autonomic) and disease phase. The evidence base for most CRPS medications is limited to small trials and expert consensus; treatment is largely extrapolated from neuropathic pain and inflammatory pain literature.

First-Line Analgesics

Neuropathic Pain Agents

Corticosteroids (Acute Inflammatory Phase)

Second-Line & Specialist Agents

Topical Therapies

Interventional Pain Procedures

Interventional procedures are performed by pain medicine specialists (FANZCA with FPM) or interventional pain physicians. They should be considered when conservative pharmacotherapy is insufficient and always in the context of active rehabilitation.

• Sympathetic nerve blocks: Stellate ganglion block (upper limb) or lumbar sympathetic block (lower limb) using local anaesthetic (bupivacaine 0.25%) ± corticosteroid, performed under fluoroscopic or ultrasound guidance. Series of 3–6 blocks at 1–2 week intervals. Evidence is mixed; best for sympathetically maintained pain confirmed on diagnostic block.
• Intravenous regional sympathetic block (Bier block): IV guanethidine or reserpine (no longer available in Australia) or bretylium — historical practice. Largely replaced by other modalities.
• Spinal cord stimulation (SCS): Implantable neuromodulation device. Evidence from the PRIDE study and others supports efficacy for refractory CRPS. Trial stimulation (7–14 days) precedes permanent implantation. Available at major Australian centres (e.g., Royal North Shore Hospital, St Vincent's Hospital Melbourne, Sir Charles Gairdner Hospital). Cost: ,000–,000 AUD (device + surgery); partially covered by private health insurance and some public hospital programs.
• Intrathecal drug delivery: Implanted intrathecal baclofen pump for refractory CRPS-related dystonia. Specialist tertiary referral only.

Opioid Use in CRPS

Evidence Base

Three randomised controlled trials (Zollinger et al., 1999 and 2007; Ekrol et al., 2014) and a systematic review (Meena et al., 2015) have evaluated vitamin C for CRPS prevention following distal radius fracture:

• Zollinger et al. (1999): RCT, n=123. Vitamin C 500 mg/day for 50 days vs. placebo. CRPS incidence: 7% vs. 22% (p=0.03). Relative risk reduction 0.68 (95% CI 0.26–0.89). NNT = 7.
• Zollinger et al. (2007): RCT, n=336. Three arms: vitamin C 200 mg/day, 500 mg/day, 1500 mg/day for 50 days. CRPS incidence: 10.1%, 2.4%, 1.8% respectively. 500 mg and 1500 mg doses superior to 200 mg. No significant difference between 500 mg and 1500 mg.
• Ekrol et al. (2014): RCT, n=336. Vitamin C 500 mg/day vs. placebo for 50 days following distal radius or scaphoid fracture. CRPS incidence lower in vitamin C group but did not reach statistical significance in intention-to-treat analysis (13.3% vs. 10.1%, p=0.41). Subgroup analysis for distal radius fracture showed benefit.

Recommended Protocol

Mechanism of Prevention

Vitamin C (ascorbic acid) is a potent water-soluble antioxidant that scavenges reactive oxygen species (ROS) generated during tissue injury and ischemia-reperfusion. In the context of CRPS prevention, proposed mechanisms include:

• Neutralisation of free radicals generated during fracture healing and surgical trauma, reducing oxidative nerve injury.
• Inhibition of nuclear factor-κB (NF-κB) activation, reducing downstream production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6).
• Modulation of substance P release from sensory nerve endings, attenuating neurogenic inflammation.
• Support of collagen synthesis and connective tissue repair, potentially reducing tissue hypoxia.

Extended Indications for Vitamin C Prophylaxis

While the strongest evidence is for distal radius fracture, international expert consensus (including the American Academy of Orthopaedic Surgeons and European guidelines) recommends considering vitamin C 500 mg/day for 50 days following:

• Ankle fractures and foot fractures
• Total knee arthroplasty and total hip arthroplasty
• Foot and ankle surgery (hallux valgus correction, hindfoot fusion)
• Any upper or lower limb injury requiring immobilisation >2 weeks

Optimal CRPS management requires a coordinated multidisciplinary approach. No single treatment modality is sufficient. The goal is functional restoration rather than complete pain elimination.

Psychological Support

Psychological comorbidity is highly prevalent in CRPS: up to 70% of patients report clinically significant depression, anxiety, or both. Kinesiophobia (fear of movement) is a major barrier to rehabilitation. Psychological interventions are not "optional extras" — they are core components of evidence-based CRPS management.

• Cognitive-behavioural therapy (CBT): Targets pain catastrophising, fear-avoidance beliefs, and maladaptive coping strategies. 8–12 sessions recommended. Available through public pain services, private psychologists (Medicare rebate Item 80110 under Mental Health Treatment Plan, up to 20 sessions/year), and some outreach programs.
• Acceptance and Commitment Therapy (ACT): Focuses on psychological flexibility, values-based living with pain, and reducing experiential avoidance. Increasingly available at Australian pain services.
• Mindfulness-based stress reduction (MBSR): 8-week structured programme. Evidence supports reduction in pain catastrophising and improved quality of life. Available at some Australian community health centres and via telehealth.
• Eye Movement Desensitisation and Reprocessing (EMDR): Emerging evidence for CRPS patients with comorbid PTSD (e.g., following traumatic injury or surgery). Specialist referral required.

Interdisciplinary Pain Rehabilitation Programme

For moderate-to-severe or refractory CRPS, admission to a formal interdisciplinary pain rehabilitation programme (IMRP) is recommended. These programmes typically involve 2–4 weeks of intensive, goal-directed therapy combining physiotherapy, occupational therapy, psychology, and pain medicine. In Australia, they are available at:

• Royal North Shore Hospital Pain Management Centre (Sydney)
• Austin Health Pain Service (Melbourne)
• Flinders Medical Centre Pain Management Unit (Adelaide)
• Sir Charles Gairdner Hospital Pain Management Centre (Perth)
• Royal Brisbane and Women's Hospital Persistent Pain Service (Brisbane)
• Various private pain management centres across capital cities

Wait times in the public system are typically 3–12 months. Telehealth triage and interim management by the GP can bridge this gap.

Treatment Algorithm Summary

Regular monitoring is essential to track disease progression, treatment response, and functional outcomes. The following assessment schedule is recommended:

Treatment Response Criteria

• Response: ≥30% reduction in NRS pain score AND clinically meaningful improvement in function (e.g., return to work, independent ADLs). Considered "clinically meaningful" even if pain persists.
• Partial response: 10–29% reduction in pain or improved function without pain reduction. Continue current treatment and consider adding or changing modality.
• Non-response: <10% reduction in pain with no functional improvement after 8–12 weeks of adequate therapy. Reassess diagnosis, consider comorbidities, escalate to next treatment tier.

1. 1. Harden RN, Bruehl S, Perez RSGM, et al. Validation of proposed diagnostic criteria (the "Budapest Criteria") for complex regional pain syndrome. Pain. 2010;150(2):268–274.
2. 2. Zollinger PE, Tuinebreijer WE, Kreis RW, Breederveld RS. Effect of vitamin C on frequency of reflex sympathetic dystrophy in wrist fractures: a randomised trial. Lancet. 1999;354(9195):2025–2028.
3. 3. Zollinger PE, Tuinebreijer WE, Breederveld RS, Kreis RW. Can vitamin C prevent complex regional pain syndrome in patients with wrist fractures? A randomized, controlled, multicenter dose-response study. J Bone Joint Surg Am. 2007;89(7):1424–1431.
4. 4. Ekrol I, Duckworth AD, Ralston SH, Court-Brown CM, McQueen MM. The influence of vitamin C on the outcome of distal radial fractures: a double-blind, randomized controlled trial. J Bone Joint Surg Am. 2014;96(17):1451–1459.
5. 5. Goebel A, Baranowski A, Maurer K, Ghiai A, McCabe C, Ambler G. Intravenous immunoglobulin treatment of the complex regional pain syndrome: a randomized trial. Ann Intern Med. 2010;152(3):152–158. (Also published in Lancet Neurology.)
6. 6. Cacchio A, De Blasis E, De Blasis V, Santilli V, Spacca G. Mirror therapy in complex regional pain syndrome type 1 of the upper limb in stroke patients. Neurorehabil Neural Repair. 2009;23(8):792–799.
7. 7. Moseley GL. Graded motor imagery is effective for long-standing complex regional pain syndrome: a randomised controlled trial. Pain. 2004;108(1–2):192–198.
8. 8. Moseley GL. Graded motor imagery for pathologic pain: a randomized controlled trial. Neurology. 2006;67(12):2129–2134.
9. 9. Birklein F, Dimova V. Complex regional pain syndrome–up-to-date. Pain Rep. 2017;2(6):e624.
10. 10. de Mos M, de Bruijn AGJ, Huygen FJPM, Dieleman JP, Stricker BHC, Sturkenboom MCJM. The incidence of complex regional pain syndrome: a population-based study. Pain. 2007;129(1–2):12–20.
11. 11. Australian Institute of Health and Welfare (AIHW). Chronic pain in Australia. Cat. no. PHE 267. Canberra: AIHW; 2020.
12. 12. Meena S, Sharma P, Gangary SK, Chowdhury B. Role of vitamin C in prevention of complex regional pain syndrome after distal radius fractures: a meta-analysis. Eur J Orthop Surg Traumatol. 2015;25(4):637–641.
13. 13. NICE Guideline [NG193]. Complex regional pain syndrome in over 16s: diagnosis and management. National Institute for Health and Care Excellence; 2018 (updated 2023).
14. 14. Marinus J, Moseley GL, Birklein F, et al. Clinical features and pathophysiology of complex regional pain syndrome. Lancet Neurol. 2011;10(7):637–648.
15. 15. Faculty of Pain Medicine, Australian and New Zealand College of Anaesthetists (ANZCA). Recommendations regarding the use of opioid analgesics in patients with chronic non-cancer pain. Melbourne: FPM ANZCA; 2022.