Electrolyte Disorders USMLE Step 1 Practice Question
A 74-year-old nursing home resident is brought to the hospital in July because of lethargy and decreased oral intake during a heat wave. Physical examination shows dry mucous membranes and poor skin turgor. Laboratory studies show sodium 158 mEq/L and serum osmolality 315 mOsm/kg. Which of the following is the most likely mechanism of his neurologic symptoms?
Answer choices
- AIncreased neuromuscular excitability from low calcium
- BCellular swelling from hypotonic extracellular fluid
- CNeuronal dehydration from hypertonic extracellular fluidCorrect answer
- DOligodendrocyte injury from rapid sodium correction
- ECardiac membrane instability from potassium excess
- FCerebral edema from impaired blood-brain barrier function
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