What are the scintigraphic findings in Complex Regional Pain Syndrome? What other radiographic tests are used?
The three phase bone scan (TPBS) has emerged as an objective diagnostic test especially if performed within the first 5 months after symptom onset. Otherwise, the results of a TPBS can vary greatly depending on how early in the course of the disease the study is performed.
In stage 1, there is an increase in blood velocity and blood pooling with early and delayed hyperfixation. The bone scan is abnormal approximately 80% of the time in this stage. A quantitative increased radiotracer uptake (ipsilateral >1.32 compared with contralateral) in the third phase of the TPBS in joints distal to trauma is characteristic.
In stage 2, there is normalization of blood velocity and blood pooling but a persistence of early and delayed hyperfixation. The bone scan is abnormal approximately half the time in this stage.
In stage 3, there is reduced blood velocity and blood pooling, and a minority of patients have early and delayed hyperfixation. Thus, a bone scan performed early in the disease is usually abnormal, but as the disease progresses, scans can be normal. A negative bone scan does not exclude the diagnosis of CRPS. An abnormal (i.e., hot) bone scan may predict a good response to corticosteroids. Note that bone scans can show bilateral involvement in 22% of cases of CRPS.
There is no clear role for computed tomography scan or magnetic resonance imaging to confirm a diagnosis of CRPS. They are used only to rule out other musculoskeletal disorders that might be confused with CRPS.
What other tests can be performed to support a diagnosis of CRPS?
Autonomic testing (resting sweat output, resting skin temperature, quantitative sudomotor axon reflex test) looking for differences between the affected and unaffected extremity is time-consuming and not practical. Stress thermography with cold exposure is sometimes useful as a screening test. Regional sympathetic nerve block (stellate ganglion or lumbar sympathetic nerve) causing transient relief from pain and dysesthesia is not diagnostic of CRPS but does confirm that the pain is mediated by the sympathetic nervous system. Synovial biopsies of affected joints demonstrate multiple abnormalities, but none are diagnostic of CRPS.