A 28-year-old man comes to the physician for a new patient evaluation. He has no physical … — USMLE Step 2 CK

A $28$ -year-old man comes to the physician for a new patient evaluation. He has no physical complaints. When asked about medication use, he admits to self-administering intramuscular testosterone for the past $2$ years to assist with bodybuilding. He denies fatigue, heat or cold intolerance, or changes in bowel habits. Vital signs are within normal limits. Physical examination reveals a heavily muscled physique, scattered cystic acne on the shoulders, and bilateral testicular atrophy. The thyroid gland is palpably normal in size without nodules.

Routine laboratory screening is performed, and results show:

Laboratory Study	Result	Reference Range
Thyroid-stimulating hormone (TSH)	$1.8$ $\mu$ U/mL	$0.4$ - $4.0$ $\mu$ U/mL
Total thyroxine (T4)	$3.2$ $\mu$ g/dL	$4.5$ - $12.0$ $\mu$ g/dL
Free thyroxine (T4)	$1.4$ ng/dL	$0.9$ - $2.4$ ng/dL
Total triiodothyronine (T3)	$65$ ng/dL	$80$ - $200$ ng/dL

Based on the laboratory findings, which of the following is the most appropriate next step in management?

Reassurance and routine follow-upCevap
B
Initiate levothyroxine therapy
C
Order magnetic resonance imaging of the brain
D
Measure serum reverse triiodothyronine levels
E
Perform a cosyntropin stimulation test

Cevap

The most appropriate next step is reassurance and routine follow-up, as the patient has normal active thyroid hormone levels (Free T4) despite low total levels due to androgen-induced reduction in thyroxine-binding globulin.

The correct answer is reassurance and routine follow-up. This patient is physiologically euthyroid, as evidenced by his normal thyroid-stimulating hormone (TSH) and normal Free T4 levels. The isolated low Total T4 and Total T3 are an artifact of decreased thyroxine-binding globulin (TBG). Approximately 99% of circulating thyroid hormone is bound to plasma proteins, primarily TBG. Exogenous androgens (such as the testosterone this patient is using for bodybuilding) inhibit the hepatic synthesis of TBG. This decreases the total carrying capacity for thyroid hormones in the blood, leading to low measured Total T4 and Total T3. However, the hypothalamic-pituitary-thyroid axis responds to any transient drop in free hormone by increasing TSH slightly to restore the Free T4 and Free T3 to normal levels. Because the active (free) fraction of the hormone is normal, the patient remains asymptomatic and requires no thyroid-specific intervention.

Adım Adım Çözüm

Analyze the patient's clinical presentation.

The patient is a healthy young man using anabolic steroids (testosterone), presenting with no symptoms of thyroid disease.

To establish the pre-test probability of true endocrine pathology versus drug-induced laboratory artifacts.

Interpret the thyroid function panel.

TSH and Free T4 are within normal limits, confirming a euthyroid state. Total T4 and Total T3 are low.

To differentiate between true thyroid dysfunction (where Free T4 would be abnormal) and isolated binding protein abnormalities.

Identify the underlying cause of the laboratory abnormalities.

Exogenous androgens decrease hepatic synthesis of thyroxine-binding globulin (TBG), lowering the total measurable pool of T4 and T3 without altering the physiologically active free hormone levels.

To explain the discrepancy between the Total and Free hormone measurements.

Determine the appropriate management.

Because the patient is physiologically euthyroid and the hypothalamic-pituitary-thyroid (HPT) axis is intact, no treatment is indicated for the thyroid values.

Intervening with thyroid hormone would be inappropriate and potentially harmful.

Anahtar Kavram

Thyroxine-binding globulin (TBG) deficiency secondary to androgen use

Tahmini Süre:1m 30s

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