Case report: Hyponatremia due to syndrome of inappropriate antidiuresis associated with normal pressure hydrocephalus.

Hyponatremia is common in hospitalized patients. Syndrome of inappropriate antidiuresis (SIAD) is a known cause of hyponatremia, with many different causes. Normal pressure hydrocephalus-related SIAD with resultant hyponatremia is a less known association. This case report is of a 77-year-old male with known normal pressure hydrocephalus (NPH) presenting with acute mental status changes and severe hyponatremia and found to have SIAD due to his NPH. A lumbar puncture quickly improved both his confusion and hyponatremia. The association between SAID and NPH is important as the management may require a lumbar puncture to improve symptoms. Emergency physicians must know this association to help make correct diagnoses and guide treatment.