[Chronic hyponatremia due to syndrome of inappropriate antidiuretic hormone secretion in an elderly patient with chronic obstructive pulmonary disease: Favorable response to oral urea].

Introduction: syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the leading cause of euvolemic hypoosmolar hyponatremia and represents a therapeutic challenge in elderly patients. Case report: we report an 81-year-old woman with severe chronic obstructive pulmonary disease (COPD) and depressive disorder treated with drugs potentially associated with SIADH, who developed chronic euvolemic hyponatremia. Discussion: fluid restriction and oral sodium supplementation were ineffective. Tolvaptan induced a rapid increase in serum sodium and was discontinued due to risk of overcorrection. Subsequently, oral urea (15 g/day) maintained serum sodium levels within the normal range throughout follow-up. In conclusion, this case supports oral urea as an effective, safe, and cost-efficient therapeutic option for chronic SIADH, particularly in elderly patients in whom vasopressin V2 receptor antagonists may carry a risk of overly rapid correction.