Iso-osmolar hyponatremia from polyethylene glycol.

Understanding and applying pathophysiological concepts to patient care is an important skill for physicians in the clinical setting. Here, we present a case that demonstrates how the application of common physiological concepts relating to the widely accepted hyponatremia algorithm led to an accurate diagnosis of hyponatremia. This case documents iso-osmolar hyponatremia caused by orally administered polyethylene glycol absorption in the gastrointestinal tract. Herein, we discuss the workup and differential diagnosis for iso-osmolar hyponatremia in juxtaposition with the pathophysiological mechanisms unique to this case. We discuss these pathophysiological mechanisms based on the patients' laboratory data and responses to therapeutic interventions.