IMPE Abstracts

Tolvaptan, a V2-receptor antagonist, is used for the treatment of chronic hyponatremia in adult patients with syndrome of inappropriate antidiuretic hormone secretion (SIADH). However, its use in children has not been established. Here we present a child case of chronic SIADH successfully treated with tolvaptan. The patient is a 5-year-old boy with congenital intracranial teratoma, complicated with hydrocephalus and severe motor and mental retardation. He has combined central hypothyroidism and chronic hyponatremia, treated with L-thyroxine, oral administration of sodium chloride at 1 g daily, and the restriction of water intake up to 600 ml/day. Sodium level has been maintained around 130 – 131 mEq/L (reference range: 136 – 144 mEq/L), uric acid 1.0 – 1.1 mg/dL (2.6 – 6.4 mg/dL), hematocrit 37-38%, and serum osmolarity of 265 mOsm/L. The patient was admitted to the hospital due to poor appetite after Covid19 vaccination. On admission, his sodium level was 121 mEq/L UA at 1.0 mg/dL, hematocrit at 30% and serum osmolarity of 244 mOsm/L. Serum AVP was detectable at 7.2 pg/mL despite the severe hyponatremia and diagnosed as having acute exacerbation of chronic SIADH. We started treatment of tolvaptan at 0.025 mg/kg/day. The dose was titrated gradually up to 0.18 mg/kg/day according to the serum sodium levels, which has been successfully maintained over 130 mEq/L. The AVP levels were detectable (0.7-1.5 pg/mL) during severe hyponatremia. Administration of sodium chloride was stopped with the improvement of serum sodium levels. To date, tolvaptan has been chronically administered for 5 months without apparent side effects. Our case suggested the usefulness and safety profile of tolvaptan in chronic SIADH in children. The close monitoring of fluid balance and serum sodium levels is necessary for the appropriate management of chronic SIADH, and the individualized dosing regimen should be considered.