SAT0669 99mtc-hdp spect/ct – a new method in early diagnosis of sacroileitis
Authors: R.A. Hemelein, Z. Besenyi, A. Bakos, L. Kovács, L. Pávics
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> 99Tc hydroxyl-disphophonate SPECT-CT (HDP SPECT-CT) is a hybrid imaging technology, which is a new modality in the examination of the sacroiliac joint. It is a high resolution, low dose structural computer tomography scan fused with a functional metabolism recording. Our aim was to investigate whether it is comparable in sensitivity with MRI, to analyse quantitatively the radioisotope uptake, to assess its potential in the assessment of inflammatory activity, and in the diagnosis of spondylarthitis (SpA). <h3>Objectives</h3> Seventeen patients (9 women, 8 men, mean age 35 years) were involved into the study from July 2016. The patients were selected according the following clinical features: inflammatory type low back pain raising the suspicion of axial SpA,<sup>17</sup> elevated CRP level,<sup>6</sup> HLA-B27 positivity,<sup>8</sup> associated oligo- or polyarthritis,<sup>5</sup> dactylitis,<sup>1</sup> enthesitis,<sup>1</sup> psoriasis,<sup>1</sup> uveitis<sup>1</sup> and inflammatory bowel disease.<sup>1</sup> All patients were therapeutic-naive for glucocorticostreroids, DMARDs or TNF-α inhibitors. <h3>Methods</h3> First, we performed examination of the sacroiliac joint with X-ray, to exclude those patients, who already had radiographic lesions. Then an MRI was performed in the following sequences: T2- weighted STIR for the bone marrow oedema (BME) and T1-weighted sequence for the fat metaplasia (FM). The HDP SPECT/CT was used within one week to examine the sacroiliac joint. Thereafter, the MRI images were fused with HDP SPECT/CT images. On the MRI images the BME (active lesion) and FM (chronic lesion), on the CT scans the sclerotic lesions (SCL, chronic lesion) were drawn manually as volume of interest (VOI). Uninvolved cortical areas were drawn on the different modality slices as reference region (ref). Then, we determined the isotope (99mTc-labelled HDP) uptake of the different lesions and areas. <h3>Results</h3> Four active sacroileitis and five chronic sacroileitis without active lesions were diagnosed according to the MRI results. On the other 8 patient's sacroiliac joints images (MRI, scintigraphy, CT scans), no inflammation-related lesions were observed. The MRI and HDP SPECT-CT findings were 100% concordant. The isotope uptake of BME was the highest, the radioisotope uptake of sclerotic lesions was moderate, whereas the isotope uptake of FM lesions was not different from the HDP uptake of reference regions. <h3>Conclusions</h3> According to the initial results, the different MRI lesions have different isotope uptake, which suggests, that the HDP SPECT/CT can distinguish the early and chronic stage of axial SpA from chronic lesions. Thank to whole body imaging technique we can have further information about disease activity and extent. The presented data are the first of our prospective study, and examinations of new patients are still in progress and we plan to investigate our SpA patients in remission to explore the utility of this new method in subclinical activity assessment. We also plan to investigate the corner lesions of the spine to find other potential uses of the HDP SPECT-CT imaging in SpA. <h3>Disclosure of Interest</h3> None declared