Background 18F-FDG PET/CT is a unique imaging technique that can assess the metabolic activity of spondyloarthritis. It thus, has a role as an effective imaging biomarker for assessing response to therapy.
Objectives To study the role of 18F-fluorodeoxyglucose positron emission tomography, computed tomography (FDG/PET-CT) in quantifying disease activity in patients with spondyloarthritis on anti tumour necrosis factor (TNF) biological disease modifying antirheumatic drugs (bDMARD). To assess the response to therapy with anti TNF bDMARD and to correlate extent of inflammation as quantified by FDG/PET-CT with measures of disease activity as well as treatment responses in the same group of patients.
Methods This was a prospective observational single center study done at a tertiary care rheumatology centre of Army Hospital Research and Referral, New Delhi. Thirty two adults with moderate to severe active Ankylosing Spondylitis were initiated on anti TNF-α bDMARD Infliximab or Etanercept.
Analysis using PET/CT consisted of quantification of 18F-FDG uptake in metabolically active lesions by measurements of their maximum standardized uptake values (SUVmax) at baseline and after 24 weeks of therapy. Change in cumulative SUVmax (CSUVmax) from baseline for each patient was denoted as ΔCSUVmax. This value was correlated with change from baseline in Ankylosing Spondylitis Disease Activity Score (ASDAS), Bath Ankylosing Spondylitis Functional Index (BASFI), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Maastricht Ankylosing Spondylitis Enthesitis Score (MASES) and Bath Ankylosing Spondylitis Metrology Index (BASMI) linear. Strength of correlation of a post therapy 50% reduction in CSUVmax (CSUVmax50) was sought with ASAS20 (Assessment of SpondyloArthritis international Society 20), ASDAS and BASDAI response.
Results Statistical significance was established for ΔCSUVmax (mean (SD) = 8.75 (8.0),95% CI of the difference=5.77-11.7; p=0.000) demonstrating significant response to 24 weeks of treatment with anti TNF biologicals. Significant correlation of ΔCSUVmax was established only with ΔBASDAI (p=0.026, r=0.405) and not with ΔASDAS-ESR or ΔASDAS-CRP. Strength of relationship of significance was established between CSUVmax50 and ASAS 20 response (p=0.044, r=4.073), BASDAI response (p=0.019, r=5.468) and ASDAS response (p=0.044, r=4.073). No adverse event related to PET/CT procedure was reported.
Conclusions 18F-FDG PET is capable of quantifying, both, baseline disease activity in patients and therapeutic response to TNFα inhibitors. CSUVmax 50 response correlates well with ASAS20, BASDAI and ASDAS responses.
Acknowledgements Department of Nuclear Medicine, Army Hospital Research and Referral, New Delhi.
Disclosure of Interest None declared