18F-fluoride PET/CT for detection of axial involvement in ankylosing spondylitis: correlation with disease activity

Aim of the current study was to evaluate the relationships between the findings of 18F-fluoride PET/CT (F-PET/CT) reflecting osteo-proliferative processes and the clinical indexes related to the disease activity. The clinical indexes are Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS). We studied 29 AS patients aged 26-69 years with a wide range of disease activity using F-PET/CT. The number of regions of high bone turnover or osteoarthritis features at the spine and at sacroiliac joints was counted. The number of F-PET/CT positive sites was significantly higher in patients with severe functional impairment and higher disease activity and it was positively related to both BASDAI (r = 0.336; P = 0.036) and ASDAS (r = 0.408; P = 0.014) while the number of degenerative features (osteoarthritis) was related neither with functional impact nor with disease activity. With a single examination, F-PET/CT accurately identifies the functional impairment and the clinical involvement of AS. The good correlation we found between the number of F-PET/CT positive sites and disease activity candidates this technique also for follow-up of AS.