What is Complex Regional Pain Syndrome (CRPS)?
Complex Regional Pain Syndrome (CRPS) is a chronic neuropathic pain disorder that develops after trauma or surgery, characterized by severe, disproportionate pain accompanied by autonomic, sensory, motor, and trophic changes in the affected limb. 1, 2
Historical Terminology
CRPS has been known by several names throughout medical history, all referring to the same condition: 1, 3, 4
- Reflex Sympathetic Dystrophy (RSD) - the most commonly used historical term 1
- Causalgia - particularly when associated with nerve injury 1, 3
- Sympathetically Maintained Pain - emphasizing the autonomic component 1
Classification System
CRPS is divided into two distinct types based on the presence or absence of identifiable nerve injury: 2, 3, 5
- CRPS Type I: Occurs without demonstrable nerve injury 2
- CRPS Type II: Develops after confirmed nerve damage 2
Treatment approaches are identical for both types, making the distinction primarily academic rather than clinically actionable. 5
Clinical Presentation
Pain Characteristics
The hallmark pain of CRPS has specific features that distinguish it from other pain syndromes: 1, 2
- Excruciating intensity that is disproportionate to the inciting injury 1, 2
- Progressive spread - pain gradually increases in both intensity and distribution within the affected limb 1, 2
- Contralateral spread - may extend to the opposite limb in some cases 1, 2
- Allodynia - severe pain triggered by light touch or minimal stimulation 1, 2
- Described as "cold burning pain" in the neuropathic component 1
Autonomic and Trophic Changes
CRPS produces visible physical changes in the affected limb: 1, 2
- Skin discoloration - changes in color and appearance 1, 2
- Hair loss in the affected region 1, 2
- Tissue changes including atrophy 1, 2, 3
- Temperature dysregulation - affected limb may feel warmer or cooler 2
- Swelling (edema) of the limb 3, 5
Motor Dysfunction
Motor impairments are a critical component often overlooked: 2, 3
- Functional limb weakness that appears disproportionate to the initial injury 2
- Decreased active range of motion 2
- Difficulty with weight-bearing activities and maintaining posture 2
- Altered movement patterns 2
- Inability to use the limb for stabilizing objects 2
Pathophysiology
Sympathetic dysregulation is proposed as a central mechanism, though the exact pathophysiology remains incompletely understood. 1 The condition involves peripheral and central sensitization, neurogenic inflammation, and maladaptive brain plasticity. 3
Diagnostic Approach
CRPS is primarily a clinical diagnosis based on history and physical examination, not laboratory testing. 2, 5, 6
Budapest Criteria
The Budapest Criteria represent the current gold standard for diagnosis, developed by expert consensus. 6, 7 Diagnosis requires: 2
- History of trauma or injury to the affected limb 2
- Evidence of autonomic dysfunction 2
- Motor and trophic changes 2
Supportive Testing
While not required for diagnosis, ancillary tests can support the clinical impression: 2, 5
- Three-phase bone scan: 78% sensitivity, 88% specificity 2
- Imaging studies to exclude alternative diagnoses 5
- Quantitative sensory testing (QST) in complex cases 7
- Skin biopsy for intraepidermal nerve fiber density (IENFD) 7
These tests serve to rule out other conditions rather than confirm CRPS. 5
Temporal Considerations
CRPS typically develops 4-6 weeks after the inciting trauma or surgery. 5 The condition is considered chronic when symptoms persist beyond 12 months. 7
Unique Placebo Response Pattern
CRPS demonstrates minimal placebo response except at very early time points (15-30 minutes), distinguishing it from many other chronic pain syndromes. 1, 8 This characteristic has important implications for treatment trials and clinical assessment.
Special Populations
In patients with diabetes, CRPS may present with severe tissue loss but minimal pain due to concomitant neuropathy, creating a diagnostic challenge. 2 This atypical presentation requires heightened clinical suspicion in diabetic patients with unexplained limb changes.
Prevalence in Specific Populations
CRPS has been documented in patients living with HIV, though its overall prevalence remains poorly characterized. 1 The condition can develop in any patient following trauma, regardless of underlying medical conditions.