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Difficulty: MediumEndocrinology and Metabolism

A 42-year-old woman comes to the physician for evaluation of a lump in her neck that she noticed two weeks ago. She has no neck pain, hoarseness, or difficulty swallowing. Over the past two months, she has experienced unintentional weight loss, frequent palpitations, and increased sweating. Vital signs show a heart rate of 110/min and a blood pressure of 135/85 mm Hg. Physical examination reveals warm, moist skin and a fine tremor of the outstretched hands. Palpation of the anterior neck demonstrates a 3-cm, firm, non-tender, mobile mass in the right lobe of the thyroid gland. A targeted bedside neck ultrasound confirms a 3.2-cm solid, hypoechoic nodule with regular margins and no microcalcifications. Laboratory testing reveals:

TestResultReference Range
Thyroid-stimulating hormone (TSH)0.01 µU/mL0.4 - 4.0 µU/mL
Free thyroxine (T4)2.6 ng/dL0.8 - 1.8 ng/dL

Which of the following is the most appropriate next step in the evaluation of this patient's nodule?

  1. Radionuclide thyroid scintigraphyAnswer
  2. B
    Fine-needle aspiration biopsy of the nodule
  3. C
    Measurement of serum calcitonin levels
  4. D
    Right thyroid lobectomy
  5. E
    Routine ultrasound follow-up in 6 to 12 months

Answer

Radionuclide thyroid scintigraphy
The correct sequence for evaluating a thyroid nodule begins with a serum TSH and a thyroid ultrasound. When the TSH is subnormal (suppressed), it indicates the presence of autonomous thyroid hormone production. The next most appropriate step is radionuclide thyroid scintigraphy (using iodine-123 or technetium-99m) to establish the functional status of the nodule. If the scan shows focal uptake isolated to the nodule ('hot' nodule), it confirms a toxic adenoma, which has an exceedingly low risk of malignancy and does not require cytological evaluation.

Step-by-Step Solution

1
Analyze the clinical and laboratory presentation.
The patient has symptoms of hyperthyroidism (weight loss, palpitations, tremor, tachycardia), a palpable 3-cm thyroid nodule, and labs showing a suppressed TSH with an elevated free T4.
Establishing the functional thyroid status (hyperthyroid vs. euthyroid/hypothyroid) is the primary branch point in the evaluation algorithm of a newly discovered thyroid nodule.
2
Determine the next step based on standard thyroid nodule guidelines.
Because the TSH is suppressed, the next indicated step is a radionuclide thyroid scan (scintigraphy).
If a patient with a thyroid nodule has a low TSH, scintigraphy is required to check if the nodule is 'hot' (hyperfunctioning). Hyperfunctioning nodules rarely harbor malignancy and typically do not require fine-needle aspiration biopsy.

Key Concept

In the evaluation of a thyroid nodule, if the initial serum TSH is subnormal, a radionuclide thyroid scan should be performed next to determine if the nodule is hyperfunctioning.
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Topics

Endocrinology and Metabolism

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