Background The prevalence of spondylitis has been estimated at between 0.3% and 0.8% of the population, depending on the country and region considered, with ankylosing forms accounting for only 0.08% of cases. Non-radiographic forms are the most frequent, potentially concerning two thirds of patients. Effective treatments for this condition have been available for a few years and the major challenge now concerns preradiographic diagnosis, despite recent progress in the use of MRI to detect active axial forms. In the absence of objective radiographic criteria, the diagnosis of these axial forms remains less than straightforward.
Objectives The aim of this study was to evaluate the value of 18-F FDG PET scans for spondylitis, without translation into conventional imaging.
Methods Inclusion criteria: We carried out an open, prospective study on seven patients meeting all the ASAS criteria for axial spondylitis, for whom two experienced rheumatologists were both in favor of a diagnosis of spondylitis. Sacroiliitus and the shiny corner sign were absent on conventional X rays.
All patients underwent at least one X ray examination of the pelvis, dorsolumbar spine and an 18-F FDG PET scan, with a machine equipped with a DISCOVERY 710-(128) gamma camera that came into operation on January 6 2014.
The results were read by two doctors specializing in nuclear medicine.
Exclusion criteria: Patients not meeting the ASAS criteria for axial spondylitis.
Patients with clinical signs of axial spondylitis and objective radiographic signs (with no signs of sacroiliitis on X ray).
Results All our patients were female, with a mean age of 41.1 years. Two patients had a family history of spondylitis, four had a family history of psoriasis and three patients were HLAB27-positive. Six patients presented inflammatory spinal pain, five had peripheral arthritis and four had enthesitic pain. Five patients presented a moderate biological inflammatory syndrome. Six patients were still taking NSAIDs at the time of the examination and four were taking at least one anti-TNF alpha antibody three months before the examination. The tracer used was 18-F FDG, for all patients. All examinations met the validity criteria, for all patients. Hypermetabolism was considered to be inflammatory if it had an intensity corresponding to a Suv max of at least 3. PET scans were found to be discriminant in two of our patients, demonstrating the presence of marked spinal and sacroiliac hypermetabolism in one of these patients and moderate spinal hypermetabolism in the other. The results were negative in the other five patients, four of whom had received anti-TNF alpha treatment during the preceding three months, potentially accounting for the negative results obtained. No tangible explanation could be identified for the remaining patient with negative PET scan findings.
Conclusions PET scans may be useful for non-radiographic forms of axial spondylitis, and could be important for diagnosis in subjects that have not received anti-TNF alpha treatment in the three months preceding the examination. Larger studies are required to confirm and extend these findings.
Disclosure of Interest None declared
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