Endocrinologist Attending Oceans Prime Diabetes and Endocrinology Toms River, New Jersey, United States
Disclosure(s):
George Altarcha, MD: No financial relationships to disclose
Background Diabetes insipidus (DI) is a rare cause of polyuria and polydipsia and is typically associated with pituitary disease, neurosurgery, trauma, or lithium exposure. In elderly patients, symptoms are frequently misattributed to aging or diabetes mellitus, leading to delayed diagnosis and risk of severe hypernatremia. Case A 72-year-old woman with hypertension and hyperlipidemia presented with two months of progressive thirst, dry mouth, and nocturia, drinking nearly one gallon of water daily. Symptoms worsened with nausea and decreased oral intake. She denied head trauma, pituitary disease, malignancy, psychiatric illness, or lithium exposure. Laboratory evaluation revealed hypernatremia with inappropriately dilute urine: serum sodium 150 mEq/L, urine osmolality 134 mOsm/kg, urine sodium < 20 mEq/L, and urine creatinine 18.6 mg/dL. Despite hypernatremia, failure to concentrate urine indicated impaired antidiuretic hormone (ADH) activity. After desmopressin administration, urine osmolality increased to 361 mOsm/kg (>160% rise), confirming preserved renal responsiveness and establishing central diabetes insipidus (CDI). Her hypernatremia and symptoms improved with DDAVP. MRI of the pituitary demonstrated abnormal homogeneous pituitary stalk thickening to 5 mm without focal nodularity, raising concern for inflammatory lymphocytic hypophysitis. Conclusion This case highlights new-onset CDI in an elderly patient without classic risk factors. Hypernatremia with hypotonic urine and a robust desmopressin response rapidly established the diagnosis. MRI findings suggest inflammatory or infiltrative pituitary pathology as a potential etiology. Clinicians should maintain a high index of suspicion for DI in older adults with polyuria and polydipsia to prevent severe dehydration and neurologic complications.
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