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Difficulty: MediumEndocrinology and Metabolism

A 52-year-old woman comes to the physician after noticing a lump in her lower neck 2 weeks ago. She also reports feeling more anxious than usual recently and has had occasional palpitations. She has no difficulty swallowing, hoarseness, or shortness of breath. Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 138/82 mm Hg, and pulse of 105/min. Physical examination reveals a 2.5-cm, firm, mobile, non-tender nodule in the right lobe of the thyroid gland. There is no cervical lymphadenopathy. Laboratory studies show:

Thyroid-stimulating hormone (TSH): 0.05 μ\mu U/mL (Normal: 0.4–4.0 μ\mu U/mL)
Free thyroxine (T4): 2.4 ng/dL (Normal: 0.8–1.8 ng/dL)

A thyroid ultrasound confirms a 2.6-cm solid, hypoechoic nodule in the right lobe with increased vascularity. Which of the following is the most appropriate next step in the evaluation of this patient?

  1. Radionuclide thyroid scanAnswer
  2. B
    Fine-needle aspiration biopsy of the nodule
  3. C
    Measurement of thyroid-stimulating immunoglobulin
  4. D
    Repeat thyroid ultrasound in 6 months
  5. E
    Right thyroid lobectomy

Answer

The most appropriate next step is a radionuclide thyroid scan to determine if the nodule is hyperfunctioning.
The correct answer identifies that a radionuclide thyroid scan is required. When evaluating a newly discovered thyroid nodule, the first step is to obtain a serum TSH level and a thyroid ultrasound. If the TSH is low (suppressed), it indicates biochemical hyperthyroidism. The next step is a radionuclide thyroid scan (using Iodine-123 or Technetium-99m) to determine whether the nodule is autonomously functioning ('hot') or non-functioning ('cold'). Hyperfunctioning nodules are rarely malignant, and no further cytological evaluation (like biopsy) is typically needed; treatment focuses on the hyperthyroidism. If the nodule is 'cold', it has a higher risk of malignancy, and a fine-needle aspiration (FNA) biopsy is indicated.

Step-by-Step Solution

1
Analyze the clinical presentation and laboratory findings.
The patient has a 2.5-cm thyroid nodule, symptoms of hyperthyroidism (anxiety, palpitations, tachycardia), a suppressed TSH, and an elevated free T4.
Establishing the biochemical thyroid status is the critical first step in evaluating any thyroid nodule.
2
Apply the diagnostic algorithm for a newly discovered thyroid nodule.
Because the TSH is subnormal, a radionuclide thyroid scan is required.
The initial evaluation of a thyroid nodule depends entirely on the TSH level. A low TSH suggests the nodule may be autonomously producing thyroid hormone (a 'hot' nodule).
3
Determine the utility of the chosen intervention compared to alternatives.
A radionuclide scan will differentiate a hot nodule (which is almost never malignant and requires treatment for hyperthyroidism) from a cold nodule (which carries a malignancy risk and requires fine-needle aspiration).
Performing FNA on a hot nodule can yield suspicious cytology (cellular atypia from hyperactivity), leading to unnecessary surgery. Therefore, the scan must precede any biopsy.

Key Concept

The initial evaluation of a thyroid nodule requires measuring TSH; if TSH is suppressed, a radionuclide thyroid scan is the next best step to determine if the nodule is hyperfunctioning.
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Topics

Endocrinology and Metabolism

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