Primary hypothyroidism in a child simulating a prolactin-secreting adenoma

Abstract

To report a case of primary hypothyroidism associated to hyperprolactinemia mimicking a prolactin secreting adenoma. A girl (10 years and 10 months old) was evaluated for hyperprolactinemia (prolactin: 317 ng/mL [1.9-25]). Diagnostic evaluation demonstrated free thyroxine (F-T4): 0.22 ng/dL (0.75-1.80) and thyroid-stimulating hormone (TSH): 135 UI/mL (0.3-5.0). Pituitary magnetic resonance imaging (MRI) showed an intrasellar and suprasellar mass measuring 1.9 x 1.7 x 1.7 cm, impinging on the optic chiasm. Due to the possibility of a pseudoprolactinoma caused by hyperplasia of the TSH and prolactin-producing cells, she was treated for the primary hypothyroidism with levothyroxine. After 2 months, F-T4, TSH, and prolactin returned to normal values. A new pituitary MRI, 8 months later, demonstrated a complete resolution of the pituitary mass confirming the initial suspicion of thyrotroph hyperplasia. This paper illustrates the importance of thyroid function investigation in patients with hyperprolactinemia and possible prolactinoma in order to avoid unnecessary surgery.