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Difficulty: MediumDiagnostic Workup and Test Sequencing

A 48-year-old man is evaluated in the primary care clinic after noticing a lump in his lower anterior neck while shaving. He reports a recent onset of increased sweating, frequent bowel movements, and an unintended weight loss of 3 kg (6.6 lbs) over the past two months. Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 134/86 mm Hg, and heart rate of 104/min. Physical examination reveals a 2.5-cm, firm, mobile, non-tender nodule in the left thyroid lobe. There is no cervical lymphadenopathy. Laboratory testing reveals a serum thyroid-stimulating hormone (TSH) level of 0.05 µU/mL (normal: 0.4–4.0 µU/mL) and a free thyroxine (T4) level of 2.6 ng/dL (normal: 0.8–1.8 ng/dL). A subsequent neck ultrasound confirms a 2.5-cm solid nodule in the left thyroid lobe without any suspicious sonographic features (e.g., no microcalcifications or irregular margins). Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?

  1. Radionuclide thyroid scintigraphyAnswer
  2. B
    Fine-needle aspiration biopsy of the nodule
  3. C
    Computed tomography of the neck with intravenous contrast
  4. D
    Measurement of serum calcitonin level
  5. E
    Routine clinical and ultrasonographic follow-up in 6 months

Answer

Radionuclide thyroid scintigraphy
The correct sequence for evaluating a newly discovered thyroid nodule begins with a serum TSH and a thyroid ultrasound. When the TSH is suppressed (as seen in this patient with biochemical and symptomatic hyperthyroidism), the most appropriate next step is radionuclide thyroid scintigraphy. This test determines whether the nodule is hyperfunctioning (a 'hot' nodule, which is almost always benign) or nonfunctioning (a 'cold' nodule). If the scan reveals a 'hot' nodule, fine-needle aspiration is not indicated, and the patient is treated for hyperthyroidism. If the scan shows a 'cold' nodule, fine-needle aspiration is then required to evaluate for malignancy.

Step-by-Step Solution

1
Analyze the clinical presentation and laboratory results.
The patient has a 2.5-cm solid thyroid nodule, symptoms of thyrotoxicosis, a suppressed TSH, and an elevated free T4.
Establishing the initial biochemical status is the first step in the algorithm for evaluating any new thyroid nodule.
2
Apply the diagnostic algorithm for a thyroid nodule with a suppressed TSH.
The guideline-indicated next step is to assess the functional status of the nodule using radionuclide thyroid scintigraphy.
If the TSH is suppressed, it is necessary to determine whether the nodule is hyperfunctioning ('hot') or non-functioning ('cold') because hyperfunctioning nodules carry an extremely low risk of malignancy and generally do not require biopsy.

Key Concept

The initial evaluation of a thyroid nodule depends on the TSH level; a suppressed TSH mandates a radionuclide thyroid scan to differentiate a benign hyperfunctioning nodule from a non-functioning nodule that requires fine-needle aspiration.
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Diagnostic Workup and Test Sequencing

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