AB0542 Poor value (lack of specificity) of na-f pet scan to predict which patients referred for possible spondylo-arthropathy, but not fulfilling asas criteria, will respond to an anti-tnf trial.
Authors: C. Darrieutort, C. Ansquer, B. L. Goff, E. Soltner, Y. Maugars, J.-M. Berthelot
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> It has been claimed that F-Na PET-scan was more sensitive than technetium bone scan and MRI to detect aseptic osteitis of SAPHO syndrome, and the same might hold true for SpA enthesitis (1). <h3>Objectives</h3> We sought to study the ability of F-Na PET-scan to enhance physican's confidence in the diagnosis of SpA and select patients who could respond to anti-TNF among those not fulfilling ASAS or other SpA criteria. <h3>Methods</h3> 32 patients referred as possible SpA were offered the possibility of a F-Na PET-scan if they had a negative MRI scan and did not fulfilled ASAS criteria for SpA (as well as Amor's, ESSG, and CASPAR criteria). A second visit (V2) was scheduled quickly after the PET-scan, and anti-TNF was prescribed if both physician's confidence in SpA diagnosis and patient's expectation of anti-TNF were strong enough. Physician's confidence in the diagnosis of SpA was recorded before F-Na PET-scan (V0), following F-Na PET-scan (V1), after V2, and, for those who tested it, after 3 months of anti-TNF (V3). FM criteria (WPI and SS scores), BASDAI, BASFI, and AS-DAS scores were collected at V0, V2 and V3. <h3>Results</h3> Na-F PET-scans showed abnormal uptake of at least one enthesis (including spinal sites) in 30/32 patients: mean of 6.0 +/- 4.67 [0 to 17] (out of the 42 possible sites). None showed signs of osteitis. Those 32 patients (12 males), were 40.3 +/- 11.7 years old, and only 7/32 (22%) were positive for HLA-B27. Mean +/- SD BASDAI at baseline was 5.99 +/- 1.76; mean BASFI 4.13 +/- 2.75 and mean AS-DAS 3.03 +/- 0.7. CRP (3.74 +/- 5.7 mg/dl) was normal in 78%. Mean WPI and SS scores were 9.1 +/- 4.2 and 5.5 +/- 2.8, respectively, and 44% patients fulfilled criteria for FM at V0. Physician's confidence in SpA diagnosis was rather low at V0 (3.86 +/- 2.14). However, as F-Na PET-scan was abnormal in 30/32 cases, this confidence raised to 5.20 +/- 2.53 after the PET-scan, and 5.42 +/- 2.56 at the end of V2 (mean increase since V0 = 1.34 +/-2.1: increment in 24/32 cases). An anti-TNF trial was then proposed to 19 patients, of whom 17 were still willing to experiment the drug. A good response (according to ASAS criteria) was observed in only 5/17 patients at V3. Physician's confidence in the diagnosis of SpA had dropped back to 3.54 +/- 2.4 at V3 (whole group). After 6 months, only 2/17 patients were still good responders to anti-TNF. 2/12 non-responders at V3 were reluctant to stop anti-TNF despite lack of significant changes in BASDAI/BASFI/AS-DAS, and 2 were given another anti-TNF despite failure of the first one, so that at 6 months 6/32 patients were still treated by anti-TNF, although only 2/32 had responded. Finally, 16/32 patients were diagnosed as FM (despite F-Na PET-scan uptakes in 15/16, mean = 6.1 +/- 4.4 sites), and only 2/32 as definite SpA (F-Na PET-scan uptakes in 10.5 +/- 9.2 sites). <h3>Conclusions</h3> Although F-Na PET scans showed uptakes of enthesis in 94% of patients, and transiently raised physician's confidence in the diagnosis of SpA in 24/32 cases, only 2 of the 17 patients thereafter treated by anti-TNF trial were improved by the drug. F-Na PET is very sensitive to detect ossifying processes but much probably lack specificity for SpA, and seems more often misleading than helpful. <h3>References</h3> Poisson T et al. Rev Rhum 77 (Suppl 3).A63 <h3>Disclosure of Interest</h3> None Declared