ESPE Abstracts

Introduction: Euvolemic hyponatremia is a typical feature of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Excessive secretion of antidiuretic hormone (ADH) leads to activation of the type 2 vasopressin receptor (AVPR2) in the kidneys, which plays a role in concentrating urine. Etiologies of SIADH include cranial surgery, intracranial malignancy, meningitis-encephalitis, cerebral hemorrhage, other cerebral pathologies, pulmonary pathologies, and drug-induced excessive ADH production. Tolvaptan suppresses water reabsorption in the collecting duct by inhibiting the AVPR2.

Case: A 3-year-old girl with growth retardation and persistent vomiting for the last 3 months, leading to the discovery of persistent hyponatremia on investigations, was referred to us. Anthropometric measurements revealed a height of 86 cm (-2.73 standard deviations [SD]) and a body weight of 10 kg (-2.75 SD). Physical examination revealed no pathological findings. In the biochemical analyses sodium level was 127 mmol/L, uric acid was 2.8 mg/dL, creatinine was 0.43 mg/dL and hematocrit was %28.3. The patient's total fluid intake was 1510 mL/24 hours, with urine output of 520 mL/24 hours, and plasma osmolality of 272 mOsm/kg. Spot urine sodium was 76.8 mmol/L, and blood pressure was normal. Given the current clinical and laboratory findings, SIADH was considered in the patient. Therefore, fluid restriction of 900cc//day, furosemide at a dose of 1-2 mg/kg/dose, and oral salt supplementation of 1g/day were initiated. In response to the patient's sodium levels persisting in the range of 121-125 mmol/L, treatment with the AVPR2 antagonist tolvaptan was initiated at a dose of 0.1 mg/kg/day. We observed that incrementally increasing the dose of tolvaptan to 0.8 mg/kg/day led to an improvement in sodium levels and normalization of urinary sodium excretion. Radiotherapy was initiated for the patient diagnosed with a 21x20x32 mm hypothalamic astrocytoma and diffuse metastatic nodular lesions in the cisterns as demonstrated on cranial MRI. At the last visit, the patient was receiving tolvaptan at a dose of 0.8 mg/kg/day, and sodium levels were within the reference range.

Result: Oral AVPR2 therapy is a suitable alternative treatment in children with inappropriate ADH who do not benefit from fluid restriction and diuretic treatment. Unfortunately, there are few studies in the literature regarding the use of tolvaptan in children. Although further studies are needed to strengthen its effectiveness and reliability, we consider tolvaptan to be a beneficial treatment option for chronic hyponatremia associated with SIADH.