A 23-year-old man with a 3-year history of schizophrenia is brought to the physician for a follow-up examination. He has

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A 23-year-old man with a 3-year history of schizophrenia is brought to the physician for a follow-up examination. He has been taking an antipsychotic medication for auditory hallucinations, paranoia, and disorganized thinking for 2 years. Physical examination shows no abnormalities. During the interview, he does not make eye contact with the physician and occasionally turns his head when no one is talking as if he hears someone. Laboratory studies show a serum sodium concentration of 120 mEq/L, urine sodium concentration of 8 mEq/L, and urine osmolality of 80 mOsmol/kg H20. Which of the following is the most likely cause of this patient's laboratory findings?


A) Destruction of the neurohypophysis
B) Hyperglycemia
C) Increased degradation of ADH (vasopressin)
D) Psychogenic polydipsia
E) Resistance to the antidiuretic action of vasopressin