High-resolution [18F]fluoride positron emission tomography of the distal interphalangeal joint in psoriatic arthritis—a bone–enthesis–nail complex

Objective. This study used high-resolution PET to explore the pattern of DIP joint bone metabolism to test the hypothesis that the nail was functionally integrated with the bone, based on patterns of distal phalange (DP) bone metabolism in PsA compared with OA and normal joints. Methods. A total of 234 DIP joints were scanned in 30 subjects (10 PsA, 10 OA, 10 healthy control) with [ 18 F]fluoride using the quad-high-density avalanche chamber nano PET scanner. The images were assessed blinded to diagnosis and symptoms for site and intensity of increased [ 18 F]fluoride uptake. Results. [ 18 F]fluoride uptake in the DP was strong relative to the intermediate phalange in both PsA and OA. In PsA there was a trend for uptake to occur in a diffuse pattern involving the entire DP. There was also greater uptake at the enthesis, the periosteum and at the tufts of the DP of PsA compared with OA. In OA, uptake was greatest in the subchondral region adjacent to known sites of osteophytosis and erosions. Both PsA and OA joints with uptake at the subchondral or periosteal bone are likely to be more symptomatic. Conclusion. This exploratory study suggested diffuse increased bone metabolism involving the entire DP, periosteum and entheses, especially in PsA. The subchondral bone and periosteum at the DP have large concentrations of enthesis attachments, including attachments from the nail, supporting the concept of an integrated nail and joint apparatus leading to a wide area of abnormal bone metabolism in PsA.