Electrolyte Disorders USMLE Step 1 Practice Question
A 72-year-old woman with SIADH secondary to small-cell lung cancer presents with confusion, headache, and nausea. Vital signs: BP 128/76, HR 92, RR 16, Temp 37.2°C, SpO2 98% on room air. Serum sodium is 118 mEq/L with osmolality of 245 mOsm/kg. Urine osmolality is 680 mOsm/kg. She denies recent seizures. She receives hypertonic saline 3% at 1 mL/kg/hr. Which of the following best describes the pathophysiology underlying her neurological symptoms?
Answer choices
- ACerebral edema from acute hyposmolarity of extracellular fluidCorrect answer
- BDirect toxicity of antidiuretic hormone on neuronal membranes
- COsmotic demyelination from overly rapid sodium correction
- DSeizures from hyperexcitability of cortical neurons due to hypernatremia
- EIncreased intracranial pressure from water retention in glial cells
- FVasogenic edema from disruption of the blood-brain barrier due to hyponatremia
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