Total-body positron emission tomography: a tool for systemic, quantitative evaluation of the inflammatory burden of psoriatic arthritis

Objectives: To test the hypothesis that recently-developed total body-positron emission tomography (TB-PET) imaging with integrated computed tomography (CT) will enable low-dose, quantitative, domain-specific evaluation of the total inflammatory burden of psoriatic arthritis (PsA), and associate with established outcome measures of the clinical domains of PsA.

Methods: Seventy-one adult participants (40 with PsA, 16 with rheumatoid arthritis (RA), and 15 with osteoarthritis (OA)) underwent 20-min TB-PET/CT scans using [18F]FDG, a glucose analogue radiotracer. [18F]FDG uptake was assessed qualitatively and quantitatively. Rheumatological examinations were performed prior to the scan. For both evaluations, domain-specific assessments included 68 joints, 6 entheses, 20 nails, axial disease and dactylitis.

Results: [18F]FDG PET uptake consistent with joint involvement and enthesitis were noted in 100% of participants with PsA. Other features included nail matrix pathology (53%), spinal involvement (60%), active sacroiliitis (13%) and dactylitis (10%). Patterns of [18F]FDG uptake in PsA differed from those in participants with RA or OA. There was a high concordance between TB-PET measures and the domain-specific assessments of joint (75%), entheseal (79%) and nail (65%) pathology. TB-PET was positive for an additional 15% joints, 20% entheses and 13% nails that were negative on clinical assessments.

Conclusion: TB-PET/CT identified inflammatory pathologies characteristic to all clinical domains of PsA and thus provided an in vivo evaluation of systemic PsA inflammatory burden. This promising tool may further contribute to identifying pathologies that may be occult, provide biomarkers to diagnose and differentiate PsA at an early stage, and to monitor early treatment response.