A case of lymphocytic hypophysitis with masked diabetes insipidus unveiled by glucocorticoid replacement.

Lymphocytic hypophysitis may involve the pituitary gland and various hormonal abnormalities. A 72-year-old man presented with euvolemic hyponatremia caused by glucocorticoid deficiency. After glucocorticoid replacement, hypernatremia in the presence of dilute urine was found. Central diabetes insipidus (DI) was confirmed later by a significant increase in urine osmolality after vasopressin administration. Brain magnetic resonance imaging showed a pituitary mass and loss of hyperintense signal in the posterior pituitary gland on T1-weighted imaging. The patient underwent a transsphenoidal adenectomy, and pathological examination of dissected tissues showed a typical finding of lymphocytic hypophysitis. Two months after surgery, the patient's central DI had resolved sufficiently that 1-desamino-8- d -arginine vasopressin therapy was discontinued without polyuria. However, he was kept on glucocorticoid and levothyroxine therapy. In conclusion, lymphocytic hypophysitis may feature a concealed central DI caused by glucocorticoid deficiency-associated hyponatremia.