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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