Pertechnetate scintigraphy in primary congenital hypothyroidism

Primary congenital hypothyroidism (PCH) is currently detected effectively b y heel-stick screening. When elevated thyrotropin (TSH) and/or decreased T4 are found in the blood of neonates, they are recalled, values are confirme d in venous blood and thyroxine replacement therapy (TRT) is immediately in stituted, thus cretinism or severe retardation is prevented. However, in a significant percentage of neonates with abnormal blood levels of T4 or TSH, the disorder is transient. To help determine the exact cause of PCH and th e possibility of transient PCH, pinhole thyroid imaging is performed 30 min after an intravenous injection of 18.5 MBq (500 mu Ci) Tc-99m-pertechnetat e (TcPT). Patients with a nonvisualized gland or patients with images sugge sting dyshormonogenesis are reevaluated at age 3-4 y to exclude transient P CH. Methods: To define the role of TcPT imaging in determining the exact et iology of PGH and the possibility of its being transient, we reviewed data from 103 neonates with PCH who had scintigraphy in our laboratory between 1 970 and 1996 and we correlated the results with clinical outcome. Results: Four patterns of thyroid scintigrams were recognized and these determined p atient classification: (a) normal in 7 patients with false-positive heel-st ick screening but normal venous blood hormone levels; (b) hypoplasia-ectopi a in 32 patients requiring lifelong TRT; (c) nonvisualization in 35 patient s-32 with agenesis requiring lifelong TRT and 3 with fetal thyroid suppress ion by maternal antibodies whose TRT was discontinued at a later age; and ( d) dyshormonogenesis (markedly increased TcPT concentration) in 29 patients -25 with permanent PCH requiring lifelong TRT and 4 with transient PCH in w hom TRT was discontinued. Of the 25 patients with dyshormonogenesis, 12 bel onged to five families with two or three siblings having the same disorder. Conclusion: TcPT thyroid scintigraphy in the neonate with PCH provides a m ore specific diagnosis, is useful for selecting patients for re-evaluation to uncover transient PCH and discontinue TRT and defines dyshormonogenesis, which is familial and requires genetic counseling. It is also cost-effecti ve.