Complex Regional Pain Syndrome (CRPS/RSD)⁹⁹ᵐTc-MDP/HDP

Quick Answer

Complex regional pain syndrome (CRPS, formerly reflex sympathetic dystrophy) is a chronic regional pain disorder, usually of a distal extremity after trauma or surgery, with disproportionate pain, vasomotor and trophic changes. The three-phase bone scan supports the diagnosis when it shows diffuse increased periarticular uptake in the affected limb — most reliably on the delayed (third) phase, in a juxta-articular distribution across multiple joints of the hand or foot. CRPS is fundamentally a clinical diagnosis (Budapest criteria); the bone scan is an adjunct — a positive delayed-phase periarticular pattern raises confidence, but sensitivity is imperfect (lower in children and in long-standing disease), so a normal scan does not exclude it.

The classic three-phase pattern

The supportive finding is increased juxta-articular (periarticular) uptake in the affected extremity, classically diffuse and involving multiple joints of the hand/wrist or foot/ankle. The delayed phase is the most useful and specific; flow and blood-pool phases may be increased (warm, early disease) or decreased (cold, later/chronic or in children). Because the pattern evolves, timing matters — early CRPS tends to be "hot" on all phases, while chronic disease can normalize or become photopenic.

What the scan adds — and its limits

The bone scan's value is objective support for a clinical impression and help distinguishing CRPS from other causes of a painful, swollen limb. But CRPS is diagnosed by the Budapest clinical criteria; imaging is not required. Reported sensitivity is variable and often modest, and is notably lower in children and in chronic disease — so a negative scan cannot rule CRPS out. The characteristic periarticular, multi-joint, delayed-phase distribution is what raises specificity above a nonspecific hot limb.

High-Yield Pearls

• The supportive sign is diffuse periarticular (juxta-articular) uptake across multiple joints, best seen on the delayed phase.
• CRPS is a clinical diagnosis (Budapest criteria) — the bone scan is an adjunct, not a gold standard.
• Findings evolve: early disease is often hot on all phases; chronic disease (and pediatric CRPS) may be normal or cold.
• A normal scan does not exclude CRPS.

Common Pitfalls

• Treating the bone scan as a rule-out test — sensitivity is imperfect, especially in children and chronic disease.
• Expecting increased flow/blood-pool in every case — later CRPS can be photopenic.
• Calling focal single-joint uptake "CRPS" — the supportive pattern is multi-joint periarticular.

Related Pages

• Protocol: Bone scintigraphy (three-phase technique).

Differential Diagnosis

• Disuse (immobilization) osteoporosis — diffuse periarticular uptake from non-use can overlap with, and be hard to separate from, CRPS.
• Osteomyelitis / septic arthritis — three-phase positive but typically focal, single-joint with intense delayed uptake, rather than the diffuse multi-joint periarticular CRPS pattern.
• Cellulitis / soft-tissue infection — increased flow and blood pool without focal delayed bony uptake.
• Inflammatory arthritis (e.g. rheumatoid) — periarticular uptake but usually bilateral and symmetric in a characteristic joint distribution.
• Recent fracture, surgery, or stress injury — focal uptake localizing to the site of injury rather than a regional multi-joint pattern.

Reporting Checklist

• Report all three phases (flow, blood pool, delayed) and state which are abnormal.
• Describe the distribution — periarticular, multi-joint, affected extremity — and compare with the contralateral side.
• Characterize the pattern as hot (early) or normal/photopenic (chronic or pediatric), noting that appearance evolves.
• State explicitly that the scan is supportive/adjunctive; CRPS is a clinical diagnosis (Budapest criteria) and a normal scan does not exclude it.
• Address alternative explanations (infection, fracture, disuse) for the observed uptake.

Self-Check

Key References

• Reviews of three-phase bone scintigraphy in CRPS; Budapest diagnostic criteria for CRPS.