White Thyroid Scintigraphy

We report the case of a 22-day-old newborn with congenital hypothyroidism with thyroid-stimulating hormone (TSH) >60 μIU/mL, and a family history of an older sister being treated for dysthyroidism; however, the mother has no history of any thyroid disease or antithyroid drugs use. First, an iodine interference was ruled out. As part of the etiological assessment, a cervical ultrasound was performed and showed a normal echo-structured thyroid gland with no detectable lesions or vascular anomalies [Figure 1]. On the other hand, a Tc 99m thyroid scintigraphy was also performed and revealed a lack of radiotracer uptake in the thyroid area in favor of a white thyroid scintigraphy. The image also showed an absence or gastric uptake of pertechnetate in regard of the gastric area [Figure 2]. The patient was treated with 50 μg/day of levothyroxine, and 1 month after treatment, the TSH was at 0.311 μIU/mL.

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Figure 1 Cervical ultrasound showing a normal echo-structured thyroid gland with no detectable lesions or vascular anomalies

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Figure 2 Tc 99m thyroid scintigraphy showing a lack of radiotracer uptake in the thyroid area and an absence or gastric uptake of pertechnetate in regard of the gastric area

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Congenital hypothyroidism is the leading cause of preventable mental retardation and growth abnormalities. It may be permanent or transient.[1] Thyroid dysgenesis is the most common etiology of neonatal hypothyroidism, and disorders of hormone synthesis are rarer.[23] Thyroid scintigraphy is currently the most important imaging test that enables the determination of the etiology in the greatest number of cases.[4] A discrepancy between ultrasound and scintigraphy results may point to an anomaly in the gene coding for the iodine transporter known as sodium/iodide symporter.[56] In fact, there is a lack of iodine uptake, and the thyroid scan is, therefore, most frequently “white,” without any contrast, whereas thyroid tissue in place is visible on ultrasound.[78] However, dyshormonogenesis cannot be ruled out, all the more as we have no data of any further investigations carried out on this patient. A syndrome of resistance to TSH can be revealed in a similar form. The phenotypic expressivity of TSH resistance is highly variable going from severe congenital hypothyroidism with thyroid gland of normal/reduced size sometimes with no uptake in the scintigraphy to mild hyperthyrotropinemia (hyperTSH) associated with an apparent euthyroid state.[9] However, the syndrome of resistance to TSH is a rare condition, so the diagnostic workup should exclude other potential causes such as TSH receptor (TSH-R) blocking antibodies that lead to chronic autoimmune hypothyroidism. Similarly, blocking TSH-R antibodies that develop in patients with Graves’ disease during pregnancy may also cause fetal hypothyroidism.[10]