FRI348 Ectopic Posterior Pituitary As A Cause Of Panhypopituitarism Presenting With Hyponatremia

Disclosure: C. Choo: None. Background: Ectopic posterior pituitary gland (EPP) can occur from defective embryogenesis affecting neuronal migration, or from neurodegeneration of the hypothalamic nuclei. While isolated growth hormone deficiency is most common, it is also associated with pan-hypopituitarism. The posterior pituitary function is often preserved. Clinical Case: We report a case of pan-hypopituitarism from congenital EPP, presenting with hyponatremia. A 63-year-old male with hyperlipidemia was admitted for gastroenteritis. Serum sodium was 106mmol/L [reference range 136-146mmol/L] on admission but he was otherwise asymptomatic and haemodynamically stable. This initially improved with intravenous fluids, however subsequently stagnated at 121mmol/L despite achieving euvolemia. Thyroid and cortisol axes were evaluated in view of persistent hyponatraemia. 8am cortisol was low at 119nmol/L with inappropriately normal ACTH 13.9 pg/mL [reference range 7.2 – 62.3 pg/mL]. Thyroid function test showed central hypothyroidism consistently on repeat testing with a low fT4 of 6.1 pmol/L and 7.7 pmol/L [reference range 8.8-14.4pmol/L] and inappropriately normal TSH of 2.98MU/L and 2.41MU/L respectively [reference range 0.65-3.70MU/L]. 1mcg short synacthen test done following suspicion of hypocortisolism peaked at 468 nmol/L. He had no symptoms or signs of hypocortisolism or hypothyroidism. He was a bachelor and had clinical features of hypogonadism including short stature (142cm), high-pitched voice, scarce sexual hair and pubescent sized testes. His mid-parental height is unknown as his parents were deceased. FSH, LH, testosterone and IGF-1 were all undetectable. Prolactin was otherwise normal 9.4ug/L [reference range 4.2-16.4ug/L]. Radiographs of the forearm showed unfused epiphyseal plates at the distal radius and ulna. Thus, the diagnosis of pan-hypopituitarism was made. Magnetic resonance imaging of the pituitary revealed a T1 hyperintense nodule at the floor of the third ventricle, suggestive of ectopic posterior pituitary. There was otherwise minimal normally enhancing tissue in the pituitary fossa, and the posterior pituitary bright spot and infundibulum were absent. He was started on hydrocortisone and subsequently levothyroxine replacement, with resolution of hyponatraemia (serum sodium 139nmol/L). He did not develop polyuria or polydipsia to suggest diabetes insipidus. Due to financial concerns however, he declined growth hormone and testosterone replacement therapy. Conclusion: Most reports of EPP are in the pediatric population often presenting with short stature. This was a seemingly ordinary case of hyponatraemia initially deemed to be from hypovolaemia. His atypical clinical features led to the eventual diagnosis of EPP with panhypopituitarism at a rather late age, highlighting the importance of a thorough clinical examination necessitating further evaluation. Presentation: Friday, June 16, 2023