Question

A university student, aged 21, visits the campus health center complaining of highly irregular menstrual periods and worsening acne. She reports menstruating only three times in the past year. Additionally, she has been troubled by thick, dark hair growing on her chin, chest, and lower abdomen, which she removes frequently. The patient takes no medications and is otherwise healthy. Her blood pressure is $112/72 \text{ mm Hg}$, and her body mass index is $23.5 \text{ kg/m}^2$. Pelvic examination reveals normal female external genitalia without clitoromegaly. A serum pregnancy test is negative.

Laboratory evaluation shows the following results:
Thyroid-stimulating hormone: $1.9 \text{ \mu U/mL}$
Prolactin: $14 \text{ ng/mL}$
Total testosterone: $78 \text{ ng/dL}$ (normal: $15$–$70 \text{ ng/dL}$)
Dehydroepiandrosterone sulfate: $310 \text{ \mu g/dL}$ (normal: $35$–$430 \text{ \mu g/dL}$)
17-hydroxyprogesterone (measured at 8:00 AM): $3,800 \text{ ng/dL}$ (normal: $< 200 \text{ ng/dL}$)

Which of the following is the most likely underlying cause of this patient's clinical presentation?