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Heterogeneity of congenital primary hypothyroidism: the importance of thyroid scintigraphy
E J Schoen1, L V dos Remedios, M Backstrom
1Department of Pediatrics, Kaiser Permanente Medical Center, Oakland, California.
Insights
Newborn screening for congenital hypothyroidism needs better diagnostic methods. Thyroid scintigraphy is recommended before treatment to identify specific causes of the condition.
Area of Science:
- Endocrinology
- Pediatrics
- Neonatology
Background:
- Current newborn screening for congenital primary hypothyroidism relies on elevated thyrotropin (TSH) and low thyroxine (T4) levels.
- This screening method cannot differentiate between transient hypothyroidism and permanent forms like athyrosis or dyshormonogenesis.
Purpose of the Study:
- To evaluate the diagnostic utility of thyroid scintigraphy in confirming congenital hypothyroidism in newborns.
- To assess the spectrum of thyroid conditions identified through screening.
Main Methods:
- Screened 166,300 infants over 6.5 years for congenital hypothyroidism.
- Utilized thyroid scintigraphy with Tc-99m and I-123 in confirmed cases.
- Analyzed anatomical and functional thyroid status in diagnosed infants.
Main Results:
- Confirmed 46 cases of congenital hypothyroidism; none had goiters.
- Thyroid scintigraphy revealed 15 infants were athyroid, 7 had ectopic/hypoplastic glands, and 18 had normally located glands.
- Identified a spectrum of thyroid abnormalities, from transient to complete absence.
Conclusions:
- Standard newborn screening for congenital hypothyroidism has limitations in specific diagnosis.
- Thyroid scintigraphy is crucial for confirming the anatomic and functional diagnosis before initiating treatment.
- Congenital hypothyroidism encompasses a range of conditions requiring precise etiological identification.
Abstract:
Current newborn screening programs in California and most of the U.S. depend for diagnosis of congenital primary hypothyroidism on demonstrating an elevated thyrotropin (TSH) level in infants with the lowest 5% to 10% of thyroxine (T4) levels by filter-paper bloodspot test. The diagnosis of primary congenital hypothyroidism based on low T4 with high TSH fails to distinguish between transient hypothyroidism, ectopic or hypoplastic thyroid, athyrosis, dyshormonogenesis, and transient hyperthyrotropinemia. We screened 166,300 newborn infants for primary congenital hypothyroidism for 6.5 years and confirmed the diagnosis in 46 cases; none of these patients had a goiter. Thyroid scintigraphy was performed in 40 with technetium-99m (Tc-99m) in the first eight cases tested and iodine-123 (I-123) in 29 of the last 32 cases. Fifteen infants were athyroid and seven had ectopic or hypoplastic glands; in 18 the thyroid gland appeared normal (present, normal location). Congenital hypothyroidism represents a spectrum of diseases from transient underactivity to complete absence of the thyroid gland. We recommend that, before starting treatment, a specific anatomic and functional diagnosis be confirmed by thyroid scintigraphy and other thyroid function tests.