68Ga-DOTATATE PET/CT Versus 18F-FDG PET/CT in TENIS Syndrome: A Head-to-Head Comparison With Elevated and Suppressed TSH Levels in Papillary Thyroid Carcinoma—A Pilot Study

Background TENIS syndrome is characterized by reduced expression of sodium-iodine symporter, rising serum thyroglobulin (Tg) levels, and negative whole-body 131 I scans. In such patients, somatostatin receptor imaging with 68 Ga-DOTATATE PET/CT (somatostatin receptor SSR PET/CT) and 18 F-FDG PET/CT (FDG PET/CT) can identify metastases and were compared under 2 conditions: elevated (eTSH) and suppressed (sTSH) TSH serum levels. Potential candidates for peptide receptor radionuclide therapy (PRRNT) were identified in 15 patients prospectively enrolled. All patients underwent 4 examinations. Images were blindly evaluated for differences in SUV max values and lesion detectability. Reference standard consisted of neck ultrasound, CT, MRI, PET/CT, biopsy, and follow-up. Three patients were received PRRNT. Results sTSH SSR PET/CT detected a greater number of cervical ( P = 0.0253 and P = 0.0176) and distant LNs ( P = 0.0253 and P = 0.0391) when compared with sTSH FDG PET/CT, respectively, in a per-patient and on a per-lesion based analysis. Likewise, eTSH SSR PET/CT detected a greater number of patients with local recurrences ( P = 0.0455) and distant LN metastases ( P = 0.0143). Per-lesion analysis revealed greater number of cervical and distant LNs ( P = 0.0337 and P = 0.0039, respectively) when compared with eTSH FDG PET/CT. There was no difference in detection of distant metastases by both tracers for lung and bone metastases (κ = 1). Both skeletal and pulmonary lesions were also detected by conventional CT part of FDG or DOTATATE PET/CT scans. TSH stimulation had no additional value in a per-patient analysis for both FDG and DOTATATE PET scans (κ varying from 0.6087 to 1). However, TSH stimulation led to more lesion identifications in DOTATATE PET/CT; most of those metastases were not confirmed by the reference standard leading to a decrease in specificity (84% vs 74%). One of 3 patients submitted to 3 cycles of PRRNT presented with a visual partial response, a 20% reduction in quantitative analyses, and stable disease regarding Tg and TgAb levels. Conclusions Patients with TENIS syndrome can be imaged with SSR PET/CT as well as FDG PET/CT with high overall accuracy regardless of TSH levels (86% to 92% and 92% to 85%, respectively, with eTSH and sTSH). SSR PET/CT detected a greater number of locoregional and distant LN metastases than FDG PET/CT with both sTSH and eTSH. One of 3 patients submitted to PRRNT presented a partial response to treatment. Our findings may impact in patient restaging, management, and theranostics strategies with radiolabeled somatostatin analogs.