A 48-year-old woman comes to the clinic for evaluation of a newly noticed lump in her ante… — USMLE Step 3

A 48-year-old woman comes to the clinic for evaluation of a newly noticed lump in her anterior neck, which she discovered while applying lotion two weeks ago. Over the past two months, she has experienced a $3\text{-kg}$ ( $6.6\text{-lb}$ ) unintentional weight loss, increased sweating, and intermittent palpitations. She denies dysphagia, hoarseness, or dyspnea. Vital signs show a blood pressure of $132/78 \text{ mm Hg}$ , a heart rate of $104\text{/min}$ , and a respiratory rate of $16\text{/min}$ . Physical examination reveals a $2.5\text{-cm}$ , firm, mobile, non-tender nodule in the right lobe of the thyroid gland. No cervical lymphadenopathy is appreciated.

Initial laboratory and imaging studies are obtained. The serum thyroid-stimulating hormone (TSH) level is $0.05 \text{ mU/L}$ (normal: $0.4-4.0 \text{ mU/L}$ ). A targeted neck ultrasound confirms a $2.5\text{-cm}$ solid, primarily hypoechoic nodule in the right thyroid lobe with regular margins and no suspicious microcalcifications.

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
Right thyroid lobectomy

Answer

Radionuclide thyroid scintigraphy

The correct next step is radionuclide thyroid scintigraphy. When a patient presents with a thyroid nodule and a suppressed TSH level (indicating biochemical hyperthyroidism), the diagnostic algorithm prioritizes determining whether the nodule is autonomously hyperfunctioning. Scintigraphy (using Iodine-123 or Technetium-99m) will reveal if the nodule is 'hot' (hyperfunctioning) or 'cold' (non-functioning). This sequencing is crucial because hot nodules are almost never malignant and do not require fine-needle aspiration (FNA), saving the patient from an unnecessary invasive procedure.

Step-by-Step Solution

Analyze the initial clinical presentation and laboratory results.

The patient has clinical symptoms of hyperthyroidism (weight loss, palpitations, tachycardia) and a suppressed TSH level (

0.05 \text{ mU/L}

Identifying the patient's biochemical thyroid status is the critical first branching point in the thyroid nodule diagnostic algorithm.

Integrate the ultrasound findings with the biochemical status.

2.5\text{-cm}

structural nodule is confirmed in the setting of biochemical thyrotoxicosis.

The presence of a discrete nodule alongside a suppressed TSH raises the question of whether the nodule itself is the source of excess hormone production, such as a toxic adenoma.

Determine the appropriate sequential diagnostic test.

Radionuclide thyroid scintigraphy is selected as the next step.

Scintigraphy differentiates between a hyperfunctioning ('hot') nodule, which is rarely malignant and does not require biopsy, and a non-functioning ('cold') nodule, which carries a higher risk of malignancy and requires fine-needle aspiration.

Key Concept

Evaluation of a thyroid nodule in the setting of a suppressed TSH requires radionuclide scintigraphy to determine functionality prior to considering any invasive biopsy.

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