During a routine health maintenance visit, a 16-year-old adolescent female and her mother … — USMLE Step 2 CK

During a routine health maintenance visit, a $16$ -year-old adolescent female and her mother express concern regarding the patient's worsening facial acne and irregular menstrual periods. Menarche occurred at age $12$ , but over the past $2$ years, her menses have become increasingly unpredictable, occurring every $3$ to $5$ months. Recently, she has also noticed the development of coarse, dark hair on her upper lip and chin. The patient takes no medications and has no other medical conditions. Her blood pressure is $112/72\text{ mmHg}$ , and her body mass index is $24\text{ kg/m}^2$ . Physical examination reveals moderate cystic acne on the face and back, as well as significant hirsutism. A transabdominal pelvic ultrasound demonstrates bilaterally enlarged ovaries with multiple small peripheral cysts.

Laboratory studies obtained the previous week show the following:

Laboratory Parameter	Patient Value	Reference Range
Thyroid-stimulating hormone (TSH)	$3.5\text{ mU/L}$	$0.5\text{--}5.0\text{ mU/L}$
Free thyroxine (T4)	$1.0\text{ ng/dL}$	$0.9\text{--}1.7\text{ ng/dL}$
Total testosterone	$85\text{ ng/dL}$	$15\text{--}70\text{ ng/dL}$
Prolactin	$12\text{ ng/mL}$	$3\text{--}30\text{ ng/mL}$
$\beta$ -hCG	Negative	Negative

Based on the clinical presentation and laboratory findings, which of the following is the most appropriate next step in the management of this patient?

Measurement of early morning serum 17-hydroxyprogesteroneAnswer
B
Initiation of combined oral contraceptive therapy
C
Initiation of levothyroxine therapy
D
Prescription of oral spironolactone
E
Administration of leuprolide acetate

Answer

Measurement of early morning serum 17-hydroxyprogesterone

The correct answer is measurement of early morning serum 17-hydroxyprogesterone. This patient presents with clinical signs of hyperandrogenism (hirsutism, severe acne), oligomenorrhea, and polycystic ovaries on ultrasound. While polycystic ovary syndrome (PCOS) is a highly likely diagnosis, it is fundamentally a diagnosis of exclusion. Non-classic congenital adrenal hyperplasia (NCCAH), most commonly due to 21-hydroxylase deficiency, can present identically to PCOS in adolescents and young adults, including the presence of polycystic ovaries on ultrasound. Therefore, a definitive diagnosis of PCOS cannot be made until NCCAH is excluded. The most appropriate next step is to measure an early morning fasting serum 17-hydroxyprogesterone level, which would be elevated in NCCAH.

Step-by-Step Solution

Identify the patient's core clinical syndrome based on history and physical examination.

The patient exhibits hyperandrogenism (hirsutism, acne) and oligo-ovulation (irregular menses every 3 to 5 months).

Recognizing this triad narrows the differential diagnosis to androgen-excess disorders.

Evaluate the provided laboratory and imaging findings.

Ultrasound shows polycystic ovaries. Prolactin and TSH are normal, ruling out hyperprolactinemia and primary thyroid dysfunction. Total testosterone is mildly elevated.

These findings are highly consistent with Polycystic Ovary Syndrome (PCOS), but they also overlap significantly with other endocrine disorders.

Determine the diagnostic requirements for Polycystic Ovary Syndrome (PCOS).

PCOS is a diagnosis of exclusion. Non-classic congenital adrenal hyperplasia (NCCAH) must be ruled out.

Because NCCAH mimics PCOS perfectly in adolescents, checking an early morning 17-hydroxyprogesterone level is mandatory before confirming PCOS.

Key Concept

Polycystic ovary syndrome (PCOS) is a diagnosis of exclusion; non-classic congenital adrenal hyperplasia must be ruled out via 17-hydroxyprogesterone testing before confirming PCOS.

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