A 52-year-old woman is evaluated in the ambulatory clinic for a routine wellness examinati… — USMLE Step 3

A 52-year-old woman is evaluated in the ambulatory clinic for a routine wellness examination. She reports feeling generally well but mentions experiencing mild, intermittent palpitations over the last three months. She denies heat intolerance, unintentional weight loss, or changes in bowel habits. She has no history of neck radiation or family history of thyroid disease. Her heart rate is $88 \text{ /min}$ and blood pressure is $126/78 \text{ mm Hg}$ . On physical examination, a $2.2 \text{ cm}$ , firm, mobile, and non-tender nodule is palpated in the right lobe of her thyroid gland. There is no cervical lymphadenopathy. Initial laboratory testing reveals a serum thyroid-stimulating hormone (TSH) level of $0.05 \text{ mU/L}$ (normal: $0.4 - 4.0 \text{ mU/L}$ ). A subsequent ultrasound of the neck confirms a $2.2 \text{ cm}$ solid, isoechoic nodule in the right thyroid lobe without suspicious sonographic features such as microcalcifications or irregular margins. Which of the following is the most appropriate next step in the diagnostic workup of this patient's nodule?

Radionuclide thyroid scintigraphyAnswer
B
Fine-needle aspiration biopsy of the nodule
C
Computed tomography of the neck with intravenous contrast
D
Measurement of serum thyroglobulin concentration
E
Repeat thyroid ultrasound in 6 months

Answer

Radionuclide thyroid scintigraphy

The correct diagnostic sequencing for a patient presenting with a thyroid nodule measuring

>1 \text{ cm}

begins with measuring serum TSH and obtaining a neck ultrasound. Once a suppressed TSH is identified, it indicates the possibility of an autonomously functioning thyroid nodule (toxic adenoma). Because hyperfunctioning ('hot') nodules are extremely rarely malignant, the standard next step is a radionuclide thyroid scan (scintigraphy). If the scan demonstrates increased uptake localized to the nodule, no biopsy is needed, and the patient is treated for hyperthyroidism. If the nodule is nonfunctioning ('cold'), the risk of malignancy is higher, and a fine-needle aspiration (FNA) biopsy is then indicated.

Step-by-Step Solution

Identify the primary clinical problem from the vignette.

A 52-year-old woman has a newly discovered

2.2 \text{ cm}

thyroid nodule with an abnormally low (suppressed) TSH level of

0.05 \text{ mU/L}

Recognizing the size of the nodule and the correlated thyroid function state is essential for applying correct diagnostic guidelines.

Apply standard diagnostic algorithms for thyroid nodules.

Guidelines dictate that the next step depends on the TSH level. Because the TSH is subnormal, the diagnostic priority shifts to assessing the nodule's functional status.

A suppressed TSH suggests the nodule may be autonomously secreting thyroid hormone. Hyperfunctioning nodules carry an extremely low risk of malignancy.

Select the correct imaging modality to assess functional status.

Radionuclide thyroid scintigraphy is selected to evaluate iodine uptake.

Scintigraphy will classify the nodule as 'hot' (hyperfunctioning), 'warm' (isofunctioning), or 'cold' (nonfunctioning). A 'hot' nodule requires no biopsy, whereas a 'cold' nodule requires fine-needle aspiration.

Key Concept

In the evaluation of a thyroid nodule measuring >1 cm, a subnormal TSH dictates that the next step in the diagnostic sequence is radionuclide thyroid scintigraphy to rule out an autonomously functioning toxic adenoma.

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