Pituitary macroadenoma presenting as severe hyponatremia: a case report.

Background: Hyponatremia is defined as a serum sodium level of less than 135 mEq/L in a patient. Although hyponatremia is not an uncommon laboratory finding, especially in the elderly, hunting for the etiology is a challenging issue for any clinician. The three first-line investigations that are required for further analysis are urine osmolality, serum osmolality, and urinary sodium levels in addition to clinical assessment of volume status.

Case Presentation: A 69-year-old previously well Sinhalese man presented with lethargy, loss of appetite, vomiting, and altered behavior of 1 week's duration. An examination revealed Glasgow Coma Scale of 13/15 and marginally low blood pressure. Initial serum sodium level was 104 mmol/L, and plasma and urinary osmolalities were 251 mOsm/kg and 305 mOsm/kg, respectively. His urinary sodium level of 158 mmol/L was suggestive of a clinical picture of a syndrome of inappropriate secretion of antidiuretic hormone. Even after correction of hyponatremia with intravenously administered 3% saline, a persistent altered behavior necessitated cerebral imaging that confirmed the presence of pituitary macroadenoma. Meanwhile, his hormone profile showed very low serum cortisol and low free tetraiodothyronine levels. An ultrasound scan of his abdomen affirmed the presence of normal adrenal glands. With intravenously administered hydrocortisone and orally administered levothyroxine replacement, he showed marked clinical improvement that supported the diagnosis of hypopituitarism.

Conclusion: Hyponatremia in the elderly is not an uncommon presentation. However, etiological diagnosis is a challenging task as there are multiple overlapping differential diagnoses.