Background/Purpose: The ASAS group has defined criteria for the diagnosis of axial or peripheral spondyloarthritis (SpA). Sacroiliac joint MRI is included in these criteria and is a pivotal tool in daily practice to evaluate the patients with suspected early and non radiographic SpA. A substantial proportion of patient responds to the ASAS criteria (i.e. the clinical arm) despite negative MRI. Positron emission tomography/computed tomography (PET/CT) is a new imaging technique of potential interest in inflammatory rheumatic diseases. PET/CT has been rarely evaluated in patients with SpA and mainly used [18 F] fluorodeoxyglucose, a marker of inflammation. [18 F] fluoride is a specific bone tracer that may have potential in SpA imaging, a condition associated with spinal ossifications and sacroiliac ankylosis.

Objectives: to evaluate the clinical utility of [18 F] fluoride PET/CT in patients with negative sacroiliac joint MRI but fulfilling the ASAS criteria for SpA.

Methods: consecutive outpatients seen for inflammatory back pain and responding to the ASAS criteria for SpA were included. Patients were previously evaluated by sacroiliac joint MRI (STIR) which must be normal (no bone marrow edema). Whole body [18 F] PET/CT was performed using a SIEMENS Biograph device. Areas of interest (spine, entheseal structures and sacroiliac joints) were examined on whole body scan for the detection of increased uptake.Increased activity was defined as an activity greater than the activity of an adjacent normal bone. Patients with defined ankylosing spondylitis (AS) and positive sacroiliac joint MRI were used as positive controls.

Results: 10 patients were evaluated (8F, 2 M, mean age : 41.8, symptom duration: 3.2 years, HLA B27 positive 9/10 ; mean BASDAI : 5.6, mean ASDAS: 2.3). 9 responded to axial SpA ASAS criteria and I to peripheral SpA ASAS criteria. They all received or had received NSAIDs. No patients had DMARD or TNF inhibitors. All the patients had normal sacroiliac joint MRI. [18 F] fluoride PET/CT did not show increase activity for any patients. 5 patients with radiographic AS and positive MRI were also evaluated: for 4 patients, active lesions were detected with [18 F] fluoride PET/CT showing increased uptake in the sacroiliac joints, the spine and sternoclavicular joints.

Conclusion: [18 F] fluoride PET/CT does not seem useful in patients with inflammatory back pain, negative MRI and responding to the ASAS criteria. Thus, using this bone tracer, PET/CT does not give additional information relevant for the diagnosis of SpA. Conversely, this imaging technique using [18 F] fluoride may be able to detect active lesions in patients with defined disease and positive MRI. Measurement and quantification of maximal standard uptake value may be useful for improving the sensibility of this imaging modality in the diagnosis of SpA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/18f-fluoride-petct-assessment-in-patients-responding-to-the-asas-criteria-for-spondyloarthritis-despite-negative-sacroiliac-joint-mri/