Endocrine Abstracts

Introduction: Thyroid tissue may be found anywhere along the course of thyroglossal duct. Sublingual thyroid is a rare type of ectopic thyroid tissue resulting from failure of the embryonic development and migration of the thyroid gland to its normal pre-laryngeal site, reaching between genio-hioid and mylohyiod muscles. In most cases, hypothyroidism develops due to inadequate hormon production. Hypothyroidism may produce pituitary enlargement secondary to thyrotroph hyperplasia. Hyperprolactinemia may occur in these cases.

Case report: We present a case of a 13-year-old girl with growth failure and severe headache. At clinical examination: height=121 cm (−4 S.D.), weight=22 kg (−3 S.D.); there was no palpable thyroid gland in the pre-tracheal region. Biochemical findings were high serum cholesterol and triglycerides. Hormonal profile diagnosed primary hypothyroidism based on high levels of TSH (37.9 μIU/ml with normal values of 0.4–7 μIU/ml) and low FT₄, associated with hyperprolactinemia; GH levels were low but responded to stimulating tests. The cervical US examination showed the absence of the thyroid tissue in its normal location and a well defined, heterogeneous and hypoechogeneous mass in sublingual region. The thyroid scan with Tc-99m O4 and the MRI confirmed the presence of sublingual thyroid tissue. Pituitary imaging by X-ray revealed an enlarged sella turcica, confirmed by MRI that described a homogeneous enhancement of the pituitary gland. L-T₄ treatment was initiated and after 5 months TSH, FT₄ and PRL returned to normal levels. At 2 years follow-up the height increased by 24 cm and menarche installed.

Conclusions: In this case the diagnosis of growth disorder was challenging, having to distinguish between pituitary tumor and primary hypothyroidism. The efficacy of the L-T₄ treatment proved that pseudoprolactinoma was caused by hyperplasia of the TSH and PRL-producing cells.