What is Complex Regional Pain Syndrome (CRPS)?

What is Complex Regional Pain Syndrome (CRPS)?

Complex Regional Pain Syndrome (CRPS) is a chronic neurological pain disorder characterized by excruciating, disproportionate pain in a limb following trauma or surgery, accompanied by sensory, autonomic, motor, and trophic abnormalities. 1, 2

Classification

CRPS is divided into two distinct types based on the presence or absence of identifiable nerve injury:

• Type I (formerly reflex sympathetic dystrophy): Occurs without documented nerve injury despite thorough clinical evaluation 1, 3
• Type II (formerly causalgia): Occurs after a confirmed nerve injury or lesion documented through clinical examination or diagnostic testing 1, 3

The critical diagnostic distinction is documentation of nerve injury—its presence defines Type II, while its absence defines Type I. 1

Clinical Presentation

Pain Characteristics

• Excruciating, burning pain that gradually increases in intensity and spreads within the affected limb, sometimes extending to the contralateral limb 1, 2
• Pain is disproportionate to the initial injury and worsens with touch or stimulation 1, 4
• The condition typically follows trauma, often minor in nature 2

Sensory Abnormalities

• Allodynia (pain from normally non-painful stimuli) and hyperalgesia (exaggerated pain response) are hallmark features 1, 3
• These sensory disturbances distinguish CRPS from other pain syndromes 1

Autonomic Dysfunction

• Temperature dysregulation with affected limb feeling warmer or cooler than the contralateral side 1
• Skin color changes (mottled, red, or pale appearance) 1, 3
• Abnormal sweating patterns (increased or decreased) in the affected limb 1

Motor Impairment

• Functional limb weakness that may appear flaccid and disproportionate to the initial injury 2
• Decreased active range of motion and altered movement patterns 2
• Difficulty with transfers, weight-bearing activities, standing, maintaining posture, and using the affected limb for stabilizing objects 2

Trophic Changes

• Hair loss, tissue changes, and skin discoloration at the pain site 1, 2
• Skin and tissue atrophy in chronic cases 4
• These changes become more prominent as the condition progresses beyond 12 months 4

Diagnosis

Clinical Criteria

• Diagnosis is primarily clinical, based on the Budapest Criteria, which require symptoms present for at least 12 months to be considered chronic 1, 4
• CRPS remains a diagnosis of exclusion, requiring ruling out other conditions that could explain the symptoms 4
• The condition does not demonstrate a placebo response except at very early time points (15-30 minutes), distinguishing it from other pain syndromes 1, 5

Imaging and Diagnostic Testing

• Three-phase bone scintigraphy is the most useful imaging modality, with pooled sensitivity of 78% and specificity of 88% 1, 2
• MRI has higher specificity (91%) but lower sensitivity (35%) for CRPS-I, making it unsuitable as a screening test 1
• For CRPS-II specifically, high-resolution ultrasound and MRI may provide additional diagnostic value by directly visualizing nerve lesions and detecting denervation changes 1
• Optional diagnostic testing may include intraepidermal nerve fiber density (IENFD) assessment and imaging evidence of regional bone demineralization 4

Pathophysiology

CRPS exhibits complex pathophysiology involving:

• Peripheral and central sensitization leading to heightened pain sensitivity 3, 4
• Neurogenic inflammation with maladaptive inflammatory responses 3, 4
• Maladaptive brain plasticity and abnormal nervous system activity 3, 4
• Potential autoimmune and psychological influences 3

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Common Pitfall: Failing to recognize that CRPS is a clinical diagnosis can lead to over-reliance on imaging studies. While three-phase bone scintigraphy is helpful, normal imaging does not exclude CRPS. 1, 2