[Hyponatremia due to syndrome of inappropriate antidiuretic hormone secretion in a childhood cancer survivor ‒ The role of oral urea in treatment].

Introduction: syndrome of inappropriate antidiuretic hormone secretion (SIADH) is one of the most common causes of euvolemic hyponatremia and is especially relevant in patients with central nervous system disorders. Case report: we present the case of a 37-year-old man with a history of cerebellar medulloblastoma treated in childhood with surgery, radiotherapy, and chemotherapy, who developed long-term endocrine sequelae and intracranial tumor recurrence in adulthood, and was admitted with symptomatic hyponatremia secondary to chronic SIADH. Evaluation showed hypoosmolar hyponatremia, elevated urinary sodium, and inappropriately high urine osmolality, after excluding adrenal insufficiency by ACTH stimulation testing and confirming adequate control of central hypothyroidism. Given the recurrence of the condition and the limited suitability of vaptans, oral urea was indicated as maintenance treatment, initially at 7.5 g/day and later at 15 g every 12 hours, achieving stabilization of serum sodium levels and good clinical tolerance. Discussion: this case highlights the diagnostic and therapeutic complexity of SIADH in neuro-oncological patients with associated endocrinopathies and supports the role of oral urea as an effective and safe therapeutic alternative.