F-sodium fluoride PET-CT visualizes both axial and peripheral new bone formation in psoriatic arthritis patients.

Purpose: As bone formation is associated with psoriatic arthritis (PsA), positron emission tomography (PET) using a F-Fluoride tracer may enable sensitive detection of disease activity. Our primary aim was to determine the feasibility of whole-body F-sodium fluoride PET-CT in clinically active PsA patients to depict new bone formation (as a reflection of disease activity) at peripheral joints and entheses. Our secondary aim was to describe F-sodium fluoride findings in the axial skeleton.

Methods: Sixteen patients (female 10/16, age 50.6 ± 8.9 years) with PsA fulfilling CASPAR criteria or with a clinical diagnosis of PsA according to the treating rheumatologist and with ≥ 1 clinically active enthesitis site were included. Of each patient, a whole-body F-sodium fluoride PET-CT scan was performed. All scans were scored for PET-positive lesions at peripheral joints, enthesis sites and the spine. Clinical disease activity was assessed by swollen/tender joint count 44, enthesitis according to MASES and SPARCC scores.

Results: Out of 1088 evaluated joints, 109 joints showed PET enhancement, mainly in the interphalangeal and metatarsal joints of the feet (14/109, 12.9%) and the distal interphalangeal joints of the hands (14/109, 12.9%). PET positivity was found at 44/464 enthesis sites, mainly at the patella tendon insertion (11/44, 25%) and quadriceps tendon insertion (10/44, 22.7%). Of the PET-positive joints and enthesis sites, respectively 18.2% and 29.5% were clinically positive; 81.8% and 70.5% of the PET-positive joints and entheses respectively were clinically asymptomatic. In 11 patients, ≥ 1 axial PET-positive lesion was observed, mainly in the cervical spine.

Conclusions: New molecular bone formation was observed on F-sodium fluoride PET-CT scans, in all domains in which PsA disease activity can be observed, with a substantial part showing no clinical symptoms.

Clinical Trial Registration: EudraCT: 2017-004,850-40, registered on 13 December 2017.