SIADH and hyponatremia with theophylline.

Objective: To report a case of possible theophylline-induced hyponatremia due to the syndrome of inappropriate antidiuretic hormone (SIADH).

Case Summary: An 88-year-old man developed severe symptomatic hyponatremia (serum sodium 112 mEq/L) associated with inappropriate natriuresis (urinary sodium 58 mEq/L) temporally related to the initiation of theophylline. The patient fulfilled the criteria for the diagnosis of SIADH after all other causes of hyponatremia were excluded.