Total Body (TB)-positron emission tomography/computed tomography with the 18F-FDG radiotracer (TB 18F-FDG PET/CT) is a valid tool for diagnosing psoriatic arthritis (PsA) and making the distinction between PsA and rheumatoid arthritis, according to a poster presentation from the American College of Rheumatology (ACR) 2021 Convergence meeting on Saturday, November 6.

The presentation was delivered by Siba P. Raychaudhuri, MD, from the University of California-Davis and the Veterans’ Administration Medical Center in Sacramento, California, on behalf of the research team.

TB 18F-FDG PET/CT, Dr Raychaudhuri explained, “captures glucose metabolism across the entire body, and provides standardized measures as surrogates for degree of inflammation such as SUVmax. So, we predicted that these indices will correlate with the existing outcome measures of the 5 clinical domains of PsA (DAPSA, Leeds Enthesitis Index, Leeds Dactylitis Index, BASDAI and NAPSI).”

The researchers recruited 15 patients diagnosed with PsA; 10 with rheumatoid arthritis (RA); and 15 with osteoarthritis (OA). All participants underwent a single-timepoint TB-PET/CT scan using the PET radiotracer 18F-FDG. The investigators quantified inflammation using maximum standardized uptake value (SUVmax) for the 3 conditions.

Among patients with PsA, the scans revealed several joints with positive findings for inflammation. “Multiple sites of enthesitis were visualized in the majority of scans (n=14/15). Furthermore, nail matrix showed increased uptake in 9/15 participants. Less frequent features included spine involvement of the supra/interspinous ligaments/bursae (n=6), sacroiliac joint (n=2), and dactylitis (n=2),” the abstract authors wrote.  

The uptake patterns and intensity were significantly different in patients with PsA compared to those with OA and RA, the study revealed. Participants with PsA showed asymmetrical affects in the joints as well as other characteristic pathologies for PsA, such as inflammation of the extensor tendon. “The relative SUVmax was significantly higher in participants with PsA compared to OA. There was a fair (68%) agreement between the DAPSA score and the PET averaged SUVmax,” the authors stated.

The results, the researchers said, indicated that “TB-PET/CT measures can identify unique pathologies of PsA compared to RA and OA such as (asymmetric synovitis of large and small joints, (ii) systemic generalized enthesitis (iii) DIP inflammation, (iv) inflammation of the extensor tendons of fingers and its association with its enthesitis and adjacent nail matrix inflammation, (v) nail matrix inflammation, (vi) dactylitis, (vii) spondyloarthritis with sacroiliitis and diffuse enthesitis of the spine,” enabling diagnosis of the extent and severity of PsA and providing identification of total inflammatory burden and subclinical pathologies.

—Rebecca Mashaw

Reference:

Raychaudhuri SP, Abdelhafez Y, SmritiKundu-Raychaudhuri S, Chaudhari A. Total-Body 18F-FDG PET/CT imaging: a tool for diagnosis and quantifying inflammatory burden of psoriatic arthritis. Presented at: American College of Rheumatology Convergence 2021; November 5-9, 2021; virtual. Abstract 0452.