What is considered the best diagnostic study for CRPS?

• A. X-ray
• B. MRI
• C. Bone scan - 3 phase technetium Tc 99m
• D. Ultrasound

Answer: (C)

CRPS is diagnosed and managed mainly on clinical features, but imaging that captures both perfusion and bone turnover can strongly support the diagnosis, especially in the early phase. A three-phase bone scan using technetium-99m does exactly that: it assesses blood flow (perfusion), soft-tissue pooling (vascular phase), and bone metabolism (delayed phase). In active CRPS, the affected limb often shows increased tracer uptake in the early perfusion phase due to vasomotor changes, with continued or even greater uptake in the delayed bone phase from increased osteoblastic activity and remodeling. This pattern is most helpful when evaluated early, when X-rays are usually still normal, making it a sensitive modality to support CRPS before structural changes appear.

By contrast, X-ray changes, if they appear at all, come later and are nonspecific; MRI can show edema or soft-tissue changes but isn’t diagnostic for CRPS and can be seen in many conditions; ultrasound can reveal swelling or other findings but does not provide the specific functional information CRPS imaging benefits from. Remember, though, that imaging is adjunctive—the Budapest clinical criteria are the mainstay for diagnosis, with imaging serving to bolster the clinical picture.