Complex Regional Pain Syndrome Types
CRPS is classified into two distinct types: Type I occurs without an identifiable nerve injury (formerly called reflex sympathetic dystrophy), while Type II occurs after a confirmed nerve injury (formerly called causalgia). 1, 2, 3
Type I (CRPS-I)
- Type I encompasses reflex sympathetic dystrophy and similar conditions where no specific nerve lesion has been identified, despite thorough clinical evaluation 1
- This type typically develops after minor trauma, surgery, or occasionally spontaneously, with pain severity disproportionate to the initial injury 3, 4, 5
- CRPS-I is the most common form, with an incidence of approximately 25 per 100,000 population 4
- Classic triggers include distal radius fractures (4-37% incidence) and carpal tunnel surgery (2-4% incidence) 4
- Female gender is a significant risk factor, with a female-to-male ratio of 4:1 4
Type II (CRPS-II)
- Type II is diagnosed when there is an identifiable nerve injury or lesion documented through clinical examination or diagnostic testing 1, 3, 6
- The presence of confirmed nerve damage distinguishes this type from Type I, though both share similar clinical presentations of pain, autonomic dysfunction, and motor impairment 3, 6
- High-resolution ultrasound and MRI may be particularly useful in Type II cases given their capability to directly visualize nerve pathology and detect signs of muscle denervation 1
Clinical Distinction Between Types
- Both types present with excruciating pain that gradually increases in intensity and spreads within the affected limb, sometimes extending to the contralateral limb 2, 7
- Sensory abnormalities including allodynia (pain from non-painful stimuli) and hyperalgesia are hallmark features in both types 2, 3
- Autonomic dysfunction with temperature dysregulation, skin color changes, and abnormal sweating patterns occurs in both classifications 2, 7
- Motor impairment including functional limb weakness and decreased active range of motion characterizes both types 2, 7
- The critical diagnostic distinction is documentation of nerve injury—its presence defines Type II, while its absence defines Type I 1, 3
Diagnostic Imaging Considerations
- Three-phase bone scintigraphy demonstrates pooled sensitivity of 78% and specificity of 88% for CRPS diagnosis, though it cannot distinguish between Type I and Type II 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, MRI may provide additional diagnostic value by directly visualizing nerve lesions and detecting denervation changes 1