A-040 Incidence of Hyponatremia and Syndrome of Inappropriate Antidiuretic Hormone in Hematolymphoid Malignancies: A Five-Year Analysis

Abstract Background Hyponatremia is a common and potentially serious complication in malignancy, arising either from the cancer itself or as a consequence of treatment. In hematolymphoid malignancies, hyponatremia has been observed in a substantial proportion of patients, with rates ranging from 20% to 50%. The Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is a primary cause of hyponatremia in this population, contributing to low serum sodium levels. Although the incidence of SIADH in hematological cancers is less well-defined compared to other malignancies such as small cell lung cancer, it remains a significant clinical concern, particularly in advanced stages of lymphoma and multiple myeloma. This study aims to assess the incidence of hyponatremia and SIADH in patients with hematolymphoid malignancies at our institution. The Schwartz and Bartter Clinical Criteria for SIADH diagnosis include serum sodium 135 mEq/L, serum osmolality 275 mOsm/kg, urine sodium 40 mEq/L, urine osmolality 100 mOsm/kg, absence of volume depletion, and exclusion of other causes. Methods This retrospective study reviewed adult patients diagnosed with hematolymphoid malignancies between January 2020 and December 2024. Inclusion criteria included patients with serum sodium concentrations of less than 135 mEq/L. Key diagnostic measures included serum osmolality, urine osmolality, and serum sodium levels, which were analyzed using indirect ion-selective electrode (ISE) methodology and a freezing point depression osmometer. SIADH was diagnosed when patients presented with hyponatremia, normal serum osmolality (275–295 mOsm/kg), and euvolemia. Descriptive statistics were used to evaluate the incidence of hyponatremia and the mean serum sodium concentrations across patient subgroups. Results Among 1,366 patients with hematolymphoid malignancies, 179 (13.10%) presented with hyponatremia, defined as serum sodium levels below 135 mEq/L. Of these, 43 patients (3.14%) met the diagnostic criteria for SIADH. The most common disorders associated with SIADH included lymphoma (n=21), followed by acute myeloid leukemia (n=9), acute lymphoid leukemia (n=8), and multiple myeloma (n=5). The mean serum osmolality was 260 mOsm/kg (SD = 9.9), with urine osmolality averaging 405 mOsm/kg (SD = 154). Serum sodium was measured at 124.51 mEq/L (SD = 3.33), and urinary sodium levels were 102.18 mEq/L (SD = 45), all indicative of SIADH. Conclusion Patients with hematolymphoid malignancies are at increased risk for developing hyponatremia, with a notable prevalence of SIADH. Both the malignancy and its associated treatments contribute to disruptions in sodium balance. The incidence of SIADH in our cohort aligns with findings from earlier studies. However, it is particularly important to note that lymphoma cases accounted for the majority of SIADH diagnoses in our cohort. This emphasizes the need for heightened vigilance in monitoring sodium levels in patients with lymphoma, a subgroup at higher risk for developing SIADH. Early identification and management of hyponatremia, particularly in the context of SIADH, are essential for optimizing patient care and improving clinical outcomes in this vulnerable population. The findings reinforce the importance of timely clinical intervention in managing electrolyte imbalances in hematolymphoid malignancies, particularly lymphoma.