INTRODUCTION: Diagnosis of congenital hypothyroidism is made during neonatal trials and thyroid hormone reposition is essential during the first days after birth in affected patients. Differential diagnosis between the three possible etiologies - agenesis, ectopy and disgenesis - is important due to malignant transformation and familial prevalence of disgenesis. Thyroid scintigraphy with 99mTc-pertechnetate or 123/131I-iodine have been used for the differential diagnosis. The patients need to interrupt the hormone therapy for one month and follow the low iodine diet for fifteen days before the study. The lack of thyroid hormone has deleterious effects upon the brain in development and the damage is estimated as loss of 3 IQ points a month without hormone before age of 4. 99mTc-sestamibi could be an alternative for the differential diagnosis of congenital hypothyroidism before the age of four, once its uptake does not depend on thyroid hormone levels.
OBJECTIVE: Evaluation of 99mTc-sestamibi thyroid scintigraphy in the differential diagnosis of congenital hypothyroidism in children, without the interruption of the hormone treatment and without the low iodine diet.
METHODS: Eight patients were included in the study, with ages between 2 and 14 (medium 4.8 years old), 4 with the diagnosis of thyroid disgenesis, 2 with agenesis and 2 with sublingual thyroid. None of the patients interrupted the hormone treatment nor was placed on the low iodine diet before the study. The images of the anterior cervical region were obtained at 5 and 20 minutes after the intravenous injection of 110 to 260 MBq (3 to 7 mCi) of 99mTc-sestamibi, using a scintillation camera equipped with LEHR collimator. The images of the seringe with the radiotracer before and after the injection were also obtained for the calculation of the uptake.
RESULTS: All four patients with the diagnosis of disgenesis showed normal or increased uptake of 99mTc-sestamibi at 5 and 20 minutes (medium uptake 0.17% at 5 minutes and 0.13% at 20 minutes). No cervical or sublingual uptake of 99mTc-sestamibi was identified in 4 patients with diagnosis of agenesis or thyroid ectopy.
CONCLUSION: Thyroid scintigraphy with 99mTc-sestamibi was efficient in the differential diagnosis of congenital hypothyroidism, identifying patients with disgenesis, without the interruption of the hormone treatment.