Review Question - QID 215099

A 22-year-old man presents to the clinic with a complaint of enlarged breasts. Over the past few months, he has noticed that both of his breasts appear larger than before. This is associated with mild tenderness and nipple sensitivity, especially when wearing a shirt. His roommate adds that the patient has been increasingly irritable lately. The patient has no prior medical history and states that he takes no medications. He drinks 5-6 alcoholic beverages on weekends. He is a collegiate swimmer. The patient’s temperature is 97.8°F (36.6°C), blood pressure is 142/78 mmHg, pulse is 86/min, and respirations are 16/min. Physical exam reveals a muscular man with facial acne and thinning hair at the crown of his head. A concentric ridge of rubbery tissue is palpated under both areolas. Testicular size is normal. Laboratory results are shown:

Hematocrit: 60%
Prolactin: 18 ng/mL (reference range: < 20 ng/mL)
Luteinizing hormone (LH): Undetectable
Beta-human chorionic gonadotropin (ß-hCG): Undetectable

Which of the following is the most likely explanation for this patient's symptoms?