SUN-580 Pituitary Hyperplasia Secondary to Primary Hypothyroidism in Pediatrics: A Diagnosis Not to Be Forgotten

Background: Pathologic pituitary hyperplasia (PH) in Pediatrics may be observed in several clinical settings. In PH secondary to primary hypothyroidism the increased TRH levels, due to a long-standing hypothyroidism state and loss of negative thyroxin feedback, causes thyrotroph and lactotroph cells hypertrophy, leading to an enlarged pituitary gland. Herein we report on two pediatric patients presenting this condition. Patient 1: A 9 year-old female was referred due to severe short stature (height Z-score: -5 SDS), face myxedema and a suprasellar mass on MRI. She had a past of headache, fatigue and learning disabilities. Laboratory evaluation showed anaemia and dyslipidemia (total cholesterol 282 mg/ dL, LDL 222 mg/dL); severe hypothyroidism: TSH 1,300 IU/L (NR 0.27-4.2), fT4 0.14 ng/dL (NR 0.93-1.7), negative thyroid antibodies TgAb 0.9 mcg/L (NR <4); and hyperprolactinemia (PRL: 110 ng/mL; NR 4.79-23.3). Her bone age was delayed (2,6 yr). Pituitary MRI revealed a 19×16×12-mm mass pushing the optic chiasm. Thyroid ultrasound revealed a diminished gland. After fourteen months on LT4 therapy, she presented catch up growth (height Z-score: -3,8 SDS); and improvement in school duties. Lab evaluation showed improvement on thyroid function (fT4 0.89 ng/dL, TSH 1.57 IU/L), PRL (18.25 ng/mL) and lipids (total cholesterol 151 mg/ dL, LDL 83 mg/dL). A follow up pituitary MRI evidenced a normal-sized pituitary gland inside a still enlarged sella. Patient 2: A 19 year-old female was referred due to severe short stature (height Z-score: -4.61 SDS), myxedema, madarosis, and delayed puberty (Tanner B2PH1). Neurological complaints were absent, except for a mild slowing of the speech. Bone age was delayed (10 yrs). Her labs showed a severe primary autoimune hypothyroidism: TSH 606.60 IU/L, fT4 < 0.023 ng/dL, anti-TPO 85.8 IU/mL (NR < 4); and a mildly elevated PRL 67.59 ng/mL. Thyroid ultrasound revealed a small gland volume with heterogeneous texture. MRI evidenced a pituitary macroadenoma measuring 11x9x8 mm. After eight months on LT4 therapy, her thyroid function (fT4 1.04ng/dL, TSH 1.48 IU/L) and PRL (11.73 ng/mL) were in the normal range. A follow up MRI revealed a normal-sized pituitary gland. Conclusion: Evaluation of the hypothalamic-pituitary axis must always be taken into account when investigating pituitary masses, since MRI alone is unable to reliably differentiate the underlying condition. In both reported cases, hormonal profile was unequivocal, unmasking the diagnosis of pituitary hyperplasia secondary to primary hypothyroidism. A specialized and integrated approach is essential to adequately define treatment and prevent unnecessary intervention.