THU239 Tolvaptan For SIADH Management In Children

Disclosure: M. Igarashi: None. T. Kashima: None. H. Doi: None. K. Yoshii: None. Y. Naiki: None. R. Horikawa: None. [Background] Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is common after brain surgery and its’ management is difficult. In Japan, tolvaptan was approved for SIADH management in adults, but there are limited reports on the use of tolvaptan for SIADH in children.We presented two cases which showed triphasic response after neurosurgery and was treated with tolvaptan for SIADH phase. We will also summarize other cases which were treated with tolvaptan for SIADH phase after neurosurgery in discussion. [Case] Case1 is a 5-month-old boy with choroid plexus papilloma.A tumor resection was performed after chemotherapy. After tumor resection, serum sodium level went up to 171 mEq/L with diluted polyuria. So he was diagnosed as diabetes insipidus and treated with vasopressin. The dose of vasopressin was decreased and it was stopped on postoperative day (POD) 6, but serum sodium level further decreased and he was diagnosed as SIADH. Water restriction and hypertonic saline administration were performed. Tolvaptan at a dose of 0.1mg/kg was administered and sodium level improved from 123 mEq/L to 137 mEq/L.However, urine volume was decreased again and sodium level went down to 132 mEq/L, so tolvaptan was administered again. After second administration of tolvaptan, polyuria lasted and sodium level went up to 145 mEq/L, which was managed with temporary use of vasopressin. Case 2 is a 6-year-old girl with craniopharyngioma. After tumor resection, polyuria was observed and she was diagnosed as diabetes insipidus, which was treated with vasopressin.On POD 4, she was diagnosed as SIADH. Since water restriction was not effective, tolvaptan was administered twice (0.1mg/kg and 0.4mg/kg respectively). After second administration of tolvaptan, due to polyuria and diluted urine sodium level went up to 161 mEq/L, which was treated with vasopressin. Diluted urine and polyuria lasted, so finally she was diagnosed as diabetes insipidus. [Discussion] Tolvaptan was used for the management of SIADH that was resistant to water restriction or salt supplementation and it was useful for improving or maintaining sodium level. However, in some case, hypernatremia due to excessive free water excretion was caused after the dose of tolvaptan was increased. The appropriate dosage of tolvaptan has not yet been established. The risk of rapid sodium elevation should be considered and monitoring of water balance and sodium level was needed after using tolvaptan. [Conclusion] Tolvaptan could be an effective option for the management of SIADH, but frequent monitoring of sodium level is needed. Presentation: Thursday, June 15, 2023