Renal Salt Wasting in Acute Myeloid Leukemia

Introduction: The idea of a salt wasting disease distinct from syndrome of inappropriate antidiuretic hormone (SIADH) has been a point of skepticism among nephrologists for decades. Discernment between hypovolemia and isovolemia easily runs afoul when fewer methods of evaluation are employed. Integrating Point Of Care Ultrasound (POCUS) bolsters confidence for clinicians trying to group patients into specific volume categories; which is demonstrated in the case below. Case Description: Our patient was a 52 yo caucasian female with cerebral palsy who was diagnosed with Acute Myeloid leukemia (AML) and admitted for platelet transfusion. Prior to her admission she had completed one cycle of azacitidine and ventecolax. She began her second cycle of chemotherapy with this admission. Nephrology was consulted for chronic hypotonic hyponatremia occurring for the past month. She was euvolemic on exam. Her urine output could not be quantified. At the time of consultation her sodium was 125 mmol/L with a serum osmolality of 272 mOsm/kg and a urine osmolality of 599 mOsm/kg. Uric acid was 2.5 g/dL Interestingly, low serum uric acid characterized the entire duration of her hyponatremia. Her urinalysis was significant for a specific gravity > 1.030 with a urine sodium, potassium, and creatinine of 77 mmol/L, 41 mmol/L, and 63 mg/dl. TSH, serum cortisol, and renal functions were normal & BNP was 43. POCUS of the inferior vena cava (IVC) was performed for further clarification of the patient’s volume status. The max IVC diameter was 0.5 cm during expiration while being completely collapsed on inspiration. Collectively, these findings painted a picture of hypovolemia, which favored a diagnosis of RSW over SIADH. Recommendations were given to hydrate with IV normal saline. Over the course of 3 days, the patient’s hypotonicity resolved and her serum sodium improved to a value of 141 mmol/L. Discussion: Resolution of our patient's hyponatremia depended on an accurate volume assessment, as overt hypovolemia excluded SIADH as a diagnosis. Improvement in serum sodium with IV fluids confirmed RSW as the cause of hyponatremia. Supplementing physical exam with POCUS was an effective tool for discerning between SIADH and the more rare diagnosis of RSW. Further research is needed into optimal diagnostic strategies for RSW, including the incorporation of POCUS, which may help to address a lack of data on the disorder's prevalence.