ESPE Abstracts

Background: Thyroid imaging is recommended to determine the aetiology of congenital hypothyroidism (CHT). Currently scintigraphy is the gold standard imaging modality. Negative scinitigraphy despite the presence of thyroid tissue may lead to a spurious diagnosis of athyreosis. Few centres routinely perform both scinitgraphy and ultrasound so that the incidence of misclassified athyreosis is unknown.

Aim: To describe the incidence of sonographically normal thyroid glands in patients scintigraphically diagnosed with athyreosis using technetium (^99mTc) and to determine if these patients have a distinct clinical phenotype when compared to patients with CHT who have normal uptake on scintigraphy.

Methods: All infants who screened positive for CHT and commenced levothyroxine treatment in the Republic of Ireland between 2007 and 2016 were identified. We identified all patients diagnosed with athyreosis on thyroid scintigraphy. Patients with no uptake on scintigraphy were invited to attend for a thyroid ultrasound scan if this had not been done previously. We re-evaluated the patients found to have a normal gland on ultrasound to establish if they had transient or permanent CHT.

Results: Four hundred and eighty-eight patients were diagnosed with CHT over this ten year period in the Republic of Ireland (incidence 1:1538 live births). Seventy-three patients had a presumed diagnosis of athyreosis with no uptake on scinitigraphy in the newborn period. Sonography demonstrated thyroid tissue (three hypoplastic thyroid glands, 15 normal glands) in 18/73 (24.6%) patients who had negative scinitgraphy. Ten of the 15 patients with a normal gland on ultrasound were eligible for re-evaluation (aged over 3 years) and of these 6 (60%) had transient CHT.

Conclusion: Absence of uptake on scintigraphy does not always correlate with athyreosis. Almost one quarter of patients with no uptake on scinitgraphy had thyroid tissue on ultrasound and of these 60% had transient CHT. Ultrasound should be performed in all patients with no uptake on scintigraphy.