Elsevier

Joint Bone Spine

Volume 82, Issue 6, December 2015, Pages 411-416
Joint Bone Spine

Original article
Sodium 18F-sodium fluoride PET failed to predict responses to TNFα antagonist therapy in 31 patients with possible spondyloarthritis not meeting ASAS criteria

https://doi.org/10.1016/j.jbspin.2015.08.012Get rights and content

Abstract

Objectives

To determine whether 18F-NaF positron-emission tomography (PET) contributes to the diagnosis of spondyloarthritis and whether observed uptakes predict the response to TNFα antagonist therapy.

Methods

We studied patients who had suspected spondyloarthritis but did not meet ASAS criteria and who were referred for an assessment of eligibility for TNFα antagonist therapy. 18F-NaF PET was offered instead of bone scintigraphy. TNFα antagonist therapy was given if the clinician's level of confidence in the diagnosis of spondyloarthritis based on 18F-NaF PET findings was ≥ 50/100.

Results

Thirty-one patients accepted to undergo 18F-NaF PET. Their mean age was 39.9 ± 11.7 years; 22% were HLA-B27-positive and none had evidence of sacroiliitis by magnetic resonance imaging. Of the 31 patients, 30 had abnormal 18F-NaF PET findings. However, of the 312 high-uptake foci, only 123 (39.4%) matched sites of pain. TNFα antagonist therapy was given to 16 patients. The treated group and untreated group (n = 15) were not significantly different for the mean number of high-uptake foci per patient (11.7 ± 8.1 vs. 8.3 ± 5.1, respectively) or for the proportion of patients with high uptake by the sacroiliac joints (13/16 [81%] vs. 8/15 [53%], respectively). In the treated group, 5 patients met ASAS response criteria after 3 months. These 5 patients were among the 9 treated patients who met Amor's modified criteria (arthritis instead of asymmetrical oligoarthritis). In the 5 responders, the 18F-NaF uptake scores were nonsignificantly lower than in the 11 nonresponders (9.0 ± 8.5 vs. 13.0 ± 6.4, respectively). In the patients for whom the 18F-NaF PET findings increased the level of confidence in the diagnosis of spondyloarthritis, this effect was short-lived.

Discussion

The positive predictive value of 18F-NaF PET for diagnosing spondyloarthritis or predicting a response to TNFα antagonist therapy seems very low. This finding is probably ascribable to poor specificity.

Section snippets

Patients

We prospectively identified consecutive patients who were referred to a single hospital-based rheumatologist between May 2011 and December 2012 for an assessment of eligibility for TNFα antagonist therapy and who met the following criteria: diagnosis by a rheumatologist of possible or probable spondyloarthritis; failure to meet ASAS criteria, with absence of suggestive SIJ abnormalities by radiography and MRI; eligibility for further diagnostic evaluation by 99mTc scintigraphy; and no

Patient characteristics

Between May 2011 and December 2012, 36 patients were offered 18F-NaF PET instead of 99mTc scintigraphy and 35 accepted (Table 2). Of these 35 patients, 2 were lost to follow-up and 1 underwent 18F-fluorodeoxyglucose PET. In a young woman, 18F-NaF PET unexpectedly disclosed two severe thoracic vascular malformations that were not visible by chest radiography; semi-emergent treatment was followed by lasting pain relief, suggesting that the pain might have been related to a mild form of

Discussion

The radiotracer 18F-NaF binds only to bone, with high affinity. Thus, 90% of the injected dose is cleared from the bloodstream within 1 hour [20]. The mechanism of 18F-NaF uptake is similar to that seen with 99mTc-bisphosphonates used for bone scintigraphy: the radiotracer binds to developing hydroxyapatite crystals. The amount of deposited 18F-NaF depends on the degree of osteoblast activity and local blood flow [21], [22]. Whether NSAID therapy affects 18F-NaF PET results has not been

Funding

None.

Disclosure of interest

Occasional interventions for Pfizer, Abbot, UCB, and Schering-Plough-Merck: Y. Maugars, B. Le Goff, and J.M. Berthelot.

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