Multifactorial Hyponatremia: Don’t Miss Ruling Out Malignancy

A 62-year-old male with a history of chronic obstructive pulmonary disease (COPD), schizoaffective disorder treated with Zoloft, type 2 diabetes mellitus, and tobacco use presented with an acute on chronic hyponatremia of 120 mEq/L. He presented with only a mild headache and endorsed recently increasing his free water intake due to a cough. Labs and physical exam findings suggested a true, euvolemic hyponatremia. Polydipsia and Zoloft-induced syndrome of inappropriate antidiuretic hormone (SIADH) were determined to be likely contributors to his hyponatremia. However, given his tobacco use, further workup was done to rule out malignancy causing hyponatremia. Chest CT did ultimately suggest malignancy and further workup was recommended. With the hyponatremia treated, the patient was discharged with recommended outpatient workup. This case serves as a reminder to consider that hyponatremia may be multifactorial and even if there is a likely cause identified, malignancy should be ruled out in patients with risk factors.