Severe Hypovolemic Hyponatremia Following Percutaneous External Biliary Drainage in a Patient With Metastatic Lung Adenocarcinoma: A Case Report.

Hyponatremia is a frequent electrolyte disorder that results from an imbalance between body water and sodium. While hypovolemic hyponatremia has been largely attributed to the loss of sodium either from the gut or the kidneys, sodium depletion caused by external biliary diversion remains a largely uncommon but underacknowledged condition. We report a case of a 78-year-old man with metastatic adenocarcinoma of the lung who developed severe symptomatic hyponatremia after a percutaneous transhepatic biliary drainage procedure for malignant obstructive jaundice due to metastases to the liver. He complained of generalized weakness, severe fatigue, and nausea. Laboratory analysis showed severe hyponatremia with a serum sodium level of 118 mmol/L, volume depletion, and acute kidney injury due to a prerenal cause. Urinalysis was compatible with extrarenal sodium loss. Further analysis revealed a high sodium concentration in the biliary drainage fluid, plus high daily bile output. These findings strongly suggested biliary sodium loss as the primary mechanism of hyponatremia. The patient was treated with cautious intravenous crystalloid administration and gradual correction of serum sodium levels. The hyponatremia completely resolved, as did the renal function. This case highlights the importance of close monitoring of fluid and electrolyte balance in patients with external biliary drainage, especially those with high-output drainage, simply due to the fact that the condition can potentially lead to severe life-threatening manifestations such as severe hyponatremia and neurological disturbances.