A patient with a subarachnoid hemorrhage admitted to the intensive care unit has been stable for several days. But about 5 days after admission, routine labs show an elevated hematocrit and hyponatremia (130 mEq/L). The plasma osmolality is low, the urine osmolality is high (350 mOsm), and urine sodium is high (45 mEq/L).You go and see the patient. Due to a baseline poor mental status you can't get much subjectively. But your exam shows hypotension, decreased skin turgor, and dry mucous membranes. Worried about hypovolemia, you administer isotonic saline. This leads to a dilute urine and correction of the hyponatremia.
Challenge: This may be an unfair case as "some authorities contend that [this disease] does not really exist." What disease am I talking about?
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Made-Up Disease
The challenge of this case is differentiating between cerebral salt wasting (the answer here) and syndrome of inappropriate secretion of ADH (SIADH) as the cause of the hyponatremia. Cerebral salt wasting can be distinguished by symptoms of hypovolemia (whereas SIADH presents with normo or hypervolemia); furthermore, isotonic saline is the treatment for cerebral salt wasting while it often worsens hyponatremia in SIADH. SIADH is treated with fluid restriction.
Source: UpToDate.
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