[Oral urea in paraneoplastic syndrome of inadequate antidiuretic hormone secretion due to small-cell carcinoma ‒ Sustained, safe, and cost-effective correction through outpatient management].

Introduction: syndrome of inappropriate antidiuretic hormone secretion (SIADH) is an important cause of euvolemic hyponatremia and may represent the first clinical manifestation of an underlying malignancy, particularly small cell lung carcinoma. Case report: we report the case of a 71-year-old active smoker who presented to the emergency department with a three-week history of encephalopathy, including disorientation, psychomotor slowing, reduced appetite, occasional night sweats, and weight loss. Initial evaluation revealed severe symptomatic hyponatremia, requiring treatment with 3 % hypertonic saline and close monitoring. Subsequent assessment fulfilled the diagnostic criteria for SIADH. A targeted etiological work-up, including imaging studies and biopsy, confirmed the presence of pulmonary small cell carcinoma. After acute management of hyponatremia, and given its persistence, oral urea was initiated, first at a dose of 15 g/day and subsequently increased to 30 g/day, achieving progressive and sustained normalization of serum sodium levels. Discussion: this case highlights the importance of considering paraneoplastic SIADH in patients with severe euvolemic hyponatremia and supports oral urea as an effective, safe, cost-effective, and practical therapeutic option for both inpatient and outpatient management of SIADH secondary to small cell lung carcinoma.