An internal medicine resident is reviewing the electronic medical record of a 50-year-old … — USMLE Step 2 CK

An internal medicine resident is reviewing the electronic medical record of a $50$ -year-old female patient who recently underwent routine laboratory screening. The patient had mentioned experiencing mild, intermittent fatigue over the last few months but otherwise felt well. She has no significant past medical history and takes no medications. The physical examination documented in the chart is entirely unremarkable, with a normal body mass index and a resting heart rate of $72/\text{min}$ . Her thyroid panel reveals a serum thyroid-stimulating hormone (TSH) level of $8.2\text{ mU/L}$ (normal: $0.5 - 5.0\text{ mU/L}$ ) and a serum free thyroxine (T4) level of $1.3\text{ ng/dL}$ (normal: $0.9 - 1.7\text{ ng/dL}$ ). Which of the following is the most accurate diagnosis based on these laboratory findings?

Subclinical hypothyroidismCevap
B
Overt primary hypothyroidism
C
Central hypothyroidism
D
Euthyroid sick syndrome
E
Thyroid hormone resistance syndrome

Cevap

Subclinical hypothyroidism

The correct answer is subclinical hypothyroidism, which is biochemically defined by an elevated serum TSH level in the presence of a normal serum free T4 level. Patients are often asymptomatic or have only mild, nonspecific symptoms such as fatigue.

Adım Adım Çözüm

Interpret the serum TSH level.

The TSH is elevated at

8.2\text{ mU/L}

TSH is the most sensitive initial indicator of primary thyroid dysfunction.

Interpret the serum free T4 level in the context of the elevated TSH.

The free T4 is within normal limits at

1.3\text{ ng/dL}

The free T4 level distinguishes between subclinical and overt primary thyroid disease.

Synthesize the laboratory findings to determine the diagnosis.

The combination of an elevated TSH and a normal free T4 indicates subclinical hypothyroidism.

Overt primary hypothyroidism would present with an elevated TSH and a low free T4, rather than a normal one.

Anahtar Kavram

Subclinical hypothyroidism is defined biochemically by an elevated serum TSH level in the presence of a normal serum free T4 level.

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