Severe Hyponatremia in Acute Myeloid Leukemia: A Rare Manifestation of Cytarabine-Induced Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

Introduction: Hyponatremia is common among patient with cancer. Patient with acute myeloid leukemia are likely to received Cytarabine and Anthracycline drug for induction. Cytarabine is an antimetabolic agent. Common toxicities of Cytarabine are myelosuppression and GI disturbances. SIADH is a rare manifestation of Cytarabine. Case Description: 52-year-old man with newly diagnosed AML who presented for chemotherapy induction. He received Cytarabine and Idarubicin as 7+3 regimen. His initial serum sodium level was 137 mmol/L prior to Cytarabine administration. His serum sodium dropped to 132 mmol/L after day 2 of Cytarabine infusion. Urine studies reveals urine osmolarity of 381, urine sodium 74 mmol/L and urine potassium 43.5 mmol/L .TSH and cortisol were within normal range. He was given salt tab and fluid restriction. His serum sodium continued to decrease to 120 mmol/L. He was then given tolvaptan 7.5 mg. His serum sodium increased to 125 mmol/L He was given tolvaptan 7.5 mg daily for 3 days. Serum sodium increased to 131 mmol/L on second day and returned to 137 mmol/L on third day of tolvaptan administration. Tolvaptan was stopped after he finished 7+3 induction regimen. His serum sodium had been normal. He did not require tolvaptan or salt tab to maintain his serum sodium. Discussion: Patient with malignancy are likely to develop hyponatremia from multiple etiologies. One of the common causes is SIADH from drug induced. Cytarabine is a common chemotherapeutic agent for acute leukemia. There are only few case reports of Cytarabine-induced SIADH. In this case, there is a casual relationship of Cytarabine and SIADH. Patient developed hyponatremia after day 2 of Cytarabine infusion. His sodium level normalized after he finished Cytarabine infusion and did not require any treatment to maintain his sodium level.