A 5-year-old boy is brought to the clinic by his parents due to rapid growth, facial acne,… — USMLE Step 2 CK

A $5$ -year-old boy is brought to the clinic by his parents due to rapid growth, facial acne, and the development of pubic hair over the past $6$ months. The parents also report that he has recently developed adult-type body odor. His height is at the $99$ th percentile for his age, whereas it was at the $50$ th percentile one year ago. His weight is at the $90$ th percentile. Vital signs are within normal limits. Physical examination reveals coarse, dark pubic hair (Tanner stage III) and facial acne. Genitourinary examination shows a stretched penile length of $6$ cm and bilaterally enlarged, symmetric testes with a volume of $8$ mL each. Neurologic examination is unremarkable.

Laboratory studies show:
Testosterone: $180$ ng/dL (Normal prepubertal: $<30$ ng/dL)
Basal luteinizing hormone (LH): $0.1$ mIU/mL (Normal prepubertal: $<0.3$ mIU/mL)
Thyroid-stimulating hormone (TSH): $1.8$ $\mu$ U/mL

A radiograph of the left hand and wrist reveals a bone age of $8$ years.

Which of the following is the most appropriate next step in the evaluation of this patient?

Administration of exogenous leuprolide and measurement of subsequent luteinizing hormone levelsCevap
B
Magnetic resonance imaging of the brain
C
Ultrasonography of the testes
D
Measurement of serum 17-hydroxyprogesterone
E
Reassurance and routine follow-up in 6 months

Cevap

Administration of exogenous leuprolide and measurement of subsequent luteinizing hormone levels

The correct next step is a GnRH stimulation test (leuprolide administration). This patient presents with precocious puberty (advanced bone age, rapid growth, virilization). His bilaterally enlarged testes (

8

mL) strongly suggest gonadotropin-dependent (central) precocious puberty (CPP). However, his basal LH is prepubertal (

0.1

mIU/mL). Because LH is secreted in a pulsatile manner, a single basal LH measurement can be falsely reassuring in early CPP. Therefore, standard algorithms mandate a GnRH stimulation test to differentiate CPP (which will show a robust LH surge) from peripheral precocious puberty (which will show a suppressed LH response).

Adım Adım Çözüm

Analyze the patient's physical examination and growth parameters.

The patient has advanced bone age, linear growth acceleration, virilization, and bilateral testicular enlargement (

8

mL).

Testicular volume

>4

mL indicates activation of the hypothalamic-pituitary-gonadal (HPG) axis, pointing toward Central Precocious Puberty (CPP) or a rare peripheral disorder like testotoxicosis.

Evaluate the laboratory results in the context of the physical exam.

Testosterone is high, confirming precocious puberty. However, the basal LH is

0.1

mIU/mL, which is in the prepubertal range (

<0.3

mIU/mL).

Because LH secretion is pulsatile, a single basal LH level may be low even in early CPP.

Determine the algorithmic next step for advanced bone age and low basal LH.

A GnRH stimulation test (using a GnRH agonist like leuprolide) must be performed.

If the stimulated LH rises to pubertal levels, it confirms CPP, and a brain MRI is the subsequent step. If the stimulated LH remains suppressed, it confirms peripheral precocious puberty (e.g., testotoxicosis), necessitating targeted imaging of the testes or adrenal glands.

Anahtar Kavram

In the evaluation of precocious puberty, bilateral testicular enlargement suggests central precocious puberty, but a GnRH stimulation test is required to biochemically confirm HPG axis activation if the basal LH is in the prepubertal range.

Soru

Cevap

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