According to study results published in The Journal of Clinical Endocrinology & Metabolism, early thyroid scintigraphy can predict permanent congenital hypothyroidism reliably in cases of agenesis or ectopic thyroid, but it cannot differentiate between permanent and transient congenital hypothyroidism in cases of eutopic thyroid.
This retrospective study of 142 full-term infants diagnosed with congenital hypothyroidism between 2000 and 2012 sought to assess clinical variables, such as early thyroid scan results, that might predict whether the diagnosis of hypothyroidism was permanent or transient.
Included infants were categorized into 3 groups: agenesis/ectopic thyroid and permanent congenital hypothyroidism, eutopic thyroid and permanent congenital hypothyroidism, or eutopic thyroid and transient congenital hypothyroidism. All infants underwent early thyroid scintigraphy and had regular follow-up at the research clinic.
Of the total population, 41% fit into the agenesis/ectopic thyroid group and 59% into the eutopic thyroid group based on classification of thyroid scans. Imaging showed similar findings in the eutopic-permanent and eutopic-transient groups.
Initial thyroid function evaluation revealed significantly higher levels of thyroid-stimulating hormone in the agenesis/ectopic group (71.5 ± 11.2 mIU/L) than in the eutopic-permanent and eutopic-transient groups (49.1 ± 27.9 mIU/L and 42.5 ± 29.1 mIU/L, respectively; P <.001).
Longitudinal follow-up indicated a consistent decrease in daily doses of L-thyroxine for the entire cohort. Compared with the eutopic-permanent group, the agenesis/ectopic group required higher L-thyroxine doses at 3 months (P <.001). Higher doses were also required at 6 months in the eutopic-permanent group than in the eutopic-transient group (P <.01).
Using receiver operating characteristic analysis, the researchers determined that among infants older than 6 months, thyroid-stimulating hormone levels higher than 63.5 mIU/L at diagnosis and L-thyroxine doses greater than 4.6 mcg/kg/day during follow-up predicted agenesis/ectopic gland (P <.001 for both). The same was true for an L-thyroxine dose greater than 2.2 mcg/kg/day for permanent congenital hypothyroidism in patients older than 6 months with a eutopic gland (P <.01).
The researchers noted several limitations to their study, including those inherent in early thyroid scintigraphy as well as an absence of genetic analysis.
“In infants with a eutopic gland, thyroid scan plays a limited role in predicting the course and outcome of congenital hypothyroidism,” said the researchers, adding, “Our findings suggest that thyroid-stimulating hormone levels at diagnosis and the L-thyroxine dose through treatment may better distinguish between permanent and transient congenital hypothyroidism.”
Oron T, Lazar L, Ben-Yishai S, et al. Permanent versus transient congenital hypothyroidism: assessment of predictive variables [published online September 28, 2018]. J Clin Endocrinol Metab. doi:10.1210/jc.2018-00362