Congenital hypothyroidism and dyshormonogenesis: Role of 123I perchlorate discharge test

Abstract

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Objectives: The aim of this study is to characterize dyshormogenesis in children with congenital hypothyroidism (CH) and orthotopic thyroid gland. Methods: In this prospective study, 14 children (5 male, 9 female, median 7,8 y) with CH and orthotopic thyroid gland were referred for reexamination around the age of 4. During neonatal period, they were diagnosed by means of TSH screening test, thyroid scintigraphy, blood analysis and ultrasonography, beginning immediately the substitutive T4 treatment. The PDT consisted in the intravenous injection of 123I-iodine (weight adapted dose). In order to quantify the absolute thyroid iodine uptake before and after the perchlorate administration, the full dose, the empty syringe (with needle) as well as anterior cervical frames of the patient 2 hours after the iodine injection and 30 and 60 minutes after the perchlorate administration (500 mg, orally) were quantified in gammacamera (same collimator, 120 sec/frame). The quantification included the absolute thyroid iodine uptake (in basal conditions and after perchlorate) and the relative thyroid iodine clearance 30 and 60 minutes after perchlorate. Results: 9/14 children showed more than 10% decrease in 123I thyroid uptake after perchlorate administration (mean 27.3 % at 30 min, 34.9 % at 60 min). The thyroid absolute iodine uptake showed similar results of thyroid clearance comparing the basal and the post-perchlorate images. In 5 cases the PDT was negative (thyroid clearance under 10 %): one transient neonatal hypothyroidism, two severe hypothyroidism with thyroglobulin defect and two mild hypothyroidism. Conclusions: Perchlorate discharge test remains very useful in conjunction with hormones (TSH, T4, TG) to make a diagnosis of organification defect in infants with CH and orthotopic thyroid and to distinguish permanent from transient CH. On the other hand, definitive diagnosis of dyshormonogenesis requires a molecular genetic analysis.