Imaging Neoangiogenesis in Rheumatoid Arthritis (INIRA) Part II: Whole-body Synovial Uptake of 99 mTc-maraciclatide is Highly Correlated with Power Doppler Ultrasound

Abstract

Rationale and objectives: Ultrasound (US) and MRI are more sensitive than clinical examination in detecting synovitis in patients with rheumatoid arthritis (RA). It is impractical however to image large numbers of joints in routine settings. ^{99 m}Tc-maraciclatide is a radio-labeled small molecule tracer which binds with high affinity to integrin αvβ3, a cell-adhesion molecule up-regulated on neoangiogenic blood vessels, and therefore has the potential to image synovial inflammation at the whole-body level. This study explores whether ^{99 m}Tc-maraciclatide joint uptake correlates and agrees with power Doppler ultrasound (PDUS) in patients with RA.

Materials and methods: Fifty patients (41 female patients, median age 55.5 years, median DAS28-CRP 4.91) underwent clinical assessment, an US scan of forty joints, and a whole-body ^{99 m}Tc-maraciclatide scan on the same day. US images were scored using the EULAR-OMERACT grading system. ^{99 m}Tc-maraciclatide scan images were scored using binary and quantitative geometric mean (GM) methods.

Results: Strong correlation was observed between PDUS total binary (r² = 0.82) and total GM ^{99 m}Tc-maraciclatide (r² = 0.72) scores. p was <0.001 for all results. For detection of PDUS signal in small joints ^{99 m}Tc-maraciclatide had a sensitivity of 78% (95% CI 72-83), specificity of 94% (93-96), positive predictive value of 72% (67-77), and a negative predictive value of 96% (95-97).

Conclusion: ^{99 m}Tc-maraciclatide imaging of joint inflammation in RA correlates strongly with PDUS. It uses technology available in any nuclear medicine department making it easily accessible with excellent potential as an alternative modality for assessing total body synovial inflammatory load.

Keywords: Imaging; Maraciclatide; Radionuclide; Rheumatoid arthritis; Ultrasound.