BACKGROUND:
Treated cases of Differentiated thyroid cancer(DTC) with Thyroglobulin(Tg) elevated, negative whole body I131 scan (TENIS) needs further evaluation.
OBJECTIVE:
To determine if 18FDG PETCT WB imaging is useful in predicting occult disease in DTC patients with TENIS.
METHODS:
51 treated DTC patients (post thyroidectomy, I131 therapy) having negative WB I131 scan but elevated stimulated Tg ( > 10 ng/ml) were enrolled for 18FDG PETCT (TSH >30uIU/ml). Based on PET findings, patients had empirical I131 therapy/TKI or surgical exploration. Patients were followed up for 12 months. Correlation between FDG PETCT and Tg levels done and a threshold for Tg above which highest predictive value of PETCT determined.
RESULTS:
Patient age, sex, histology, tumour size, extrathyroid extension, focality, N stage correlated and found to have not significantly associated with positive FDG PETCT results (P > 0.05). AntiTgAb levels found to be statistically significant in predicting positive PET findings (P < 0.05). Compared with TgAb level <150 IU/mL, univariate regression analysis showed that Odd Ratio value of TgAb level ≥ 150 IU/mL at diagnosis and span for progressively increased TgAb level were as much as 4.18 [CI:1.52–11.54] and 3.60 [CI:1.24–10.41] times for progressively increased TgAb level.
A threshold Tg value of > 25ng/ml found to predict highest PET positive disease burden
PET positive loco regional recurrence in 16%, pulmonary parenchymal lesions in 34 % & 3% skeletal lesions were found. Sensitivity, specificity, PPV, NPV and diagnostic accuracy of PET to predict recurrence at follow-up were 68.8, 78.3, 86.8, 54.5 and 71.9%, respectively. Sensitivity, accuracy and PPV of PET increased with increasing Tg levels.
CONCLUSION:
Our study shows that FDG PETCT is incremental in identification and predicting recurrence in DTC with TENIS syndrome. Predictive value of PET was highest at Tg > 25ng/ml with sensitivity of 76.2%, specificity of 100% to detect recurrence.