A 35-year-old man visits his physician with complaints of sudden onset of fatigue,polydipsia,and polyuria.Laboratory results indicate a normal fasting blood sugar.Serum sodium was slightly elevated.The most likely cause of these symptoms and laboratory results would be:

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The patient's symptoms of polydipsia (excessive thirst) and polyuria (excessive urination) suggest a water metabolism disorder. The slightly elevated serum sodium is also a clue. The normal fasting blood sugar rules out diabetes mellitus. Pituitary adenoma and secondary hypothyroidism are less likely to cause these symptoms. Therefore, the most likely cause of these symptoms and laboratory results would be diabetes insipidus due to hypothalamic dysfunction.

A 35-Year-Old Man Visits His Physician with Complaints of Sudden