Complex Regional Pain Syndrome, Type I

(Reflex Sympathetic Dystrophy)

Definition
CRPS Type I is a syndrome that usually develops after an initiating noxious event, is not limited to the distribution of a single peripheral nerve, and is apparently disproportionate to the inciting event. It is associated at some point with evidence of edema, changes in skin blood flow, abnormal sudomotor activity in the region of the pain, or allodynia or hyperalgesia.

Site
Usually the distal aspect of an affected extremity or with a distal to proximal gradient.

Main Features
Pain often follows trauma, which is usually mild and is not associated with significant nerve injury. It may follow a fracture, a soft tissue lesion, or immobilization related to visceral disease, e.g., angina or stroke. The onset of symptoms usually occurs within one month of the inciting event. The pain is frequently described as burning and continuous and exacerbated by movement, continuous stimulation, or stress. The intensity of pain fluctuates over time, and allodynia or hyperalgesia may be found which are not limited to the territory of a single peripheral nerve. Abnormalities of blood flow occur including changes in skin temperature and color. Edema is usually present and may be soft or firm. Increased or decreased sweating may appear. The symptoms and signs may spread proximally or involve other extremities. Impairment of motor function is frequently seen.

Associated Symptoms and Signs
Atrophy of the skin, nails, and other soft tissues, alterations in hair growth, and loss of joint mobility may develop. Impairment of motor function can include weakness, tremor, and, in rare instances, dystonia.
Symptoms and signs fluctuate at times. Sympathetically maintained pain may be present and may be demonstrated with pharmacological blocking or provocation techniques. Affective symptoms or disorders occur secondary to the pain and disability. Guarding of the affected part is usually observed.

Laboratory Findings
Noncontact skin temperature measurement indicates a side-to-side asymmetry of greater than 1°C. Due to the unstable nature of the temperature changes in this disorder, measurements at different times are recommended. Measurements of skin blood flow may show an increase or a reduction. Testing of sudomotor function, both at rest and evoked, indicates side-to-side asymmetry. The bone uptake phase of a three-phase bone scan may reveal a characteristic pattern of subcutaneous blood pool changes. Radiographic examination may demonstrate patchy bone demineralization.