Osteoarthritis and fibroblast activation: an imaging study assessing feasibility and reliability of whole-body...

Primary aim was to evaluate whether presence of osteoarthritis (OA), as assessed by ordinal grading on whole-body computed tomography (CT), is associated with ⁶⁸ Ga fibroblast activation protein inhibitor (FAPI) positron emission tomography (PET) tracer uptake as a measure of fibroblastic activation. Secondary aim was to evaluate whether OA disease severity is positively correlated with increased tracer uptake and to evaluate reliability.

In a retrospective study design, patients who had undergone ⁶⁸ Ga-FAPI PET-CT for a spectrum of clinical reasons were included. Whole-body CT was assessed for OA using the OsteoArthritis Computed Tomography-Score in multiple joints and the spine. Maximum standard uptake value (SUV_max) was determined correspondingly. Logistic regression and correlation analyses were used to describe associations between structural OA and ⁶⁸ Ga-FAPI PET activity.

Fifty-four patients were included. Presence of OA in the acromioclavicular joints (ACJ) was associated with odds of SUV_max being in the highest tertile. Increased odds were seen for one location of the cervical spine (OR 5.7, 95% confidence interval [1.6, 20.4]) and both locations of the lumbar spine (OR 8.3, 95% confidence interval [1.5, 46.6]; 5.0, 95% confidence interval [1.3, 18.7]). Moderate correlations were observed for OA severity and ⁶⁸ Ga-FAPI PET uptake for most joints and spine. Reliability for OA scoring (overall percent agreement) ranged from 40 to 100% (intra-reader) and from 66.3 to 100% (inter-reader). Mean intraclass correlation coefficients for SUV_max were 0.76 and 0.82, respectively.

Presence of OA was associated with increased SUV_max uptake for the ACJ and the cervical and lumbar spine. In this feasibility study, CT-based OA scoring and ⁶⁸ Ga-FAPI PET SUV_max determinations could be achieved with good reliability.