Severe Hyponatremia Caused by the Syndrome of Inappropriate Antidiuresis Due to Urinary Retention.

We present a case of a 90-year-old female patient with severe hyponatremia due to syndrome of inappropriate antidiuresis (SIAD) induced by urinary retention. The patient had a history of neurogenic bladder and developed fatigue that progressively worsened over 10 days prior to admission. Initial treatment with hypertonic saline and bladder catheterization led to improvements in her serum sodium levels and symptoms. Based on her clinical course and laboratory findings, urinary retention was determined to be the underlying cause of SIAD. This case highlights that, although rare, urinary retention should be considered a potential trigger for SIAD in patients with unexplained hyponatremia. After relieving urinary retention, suppression of antidiuretic hormone secretion can occur, sometimes leading to rapid correction of serum sodium levels. Therefore, careful monitoring of sodium levels is required to prevent complications such as osmotic demyelination syndrome.