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Difficulty: MediumEndocrinology and Metabolism

A 45-year-old woman comes to the clinic for evaluation of a neck lump she noticed in the mirror while swallowing. She reports feeling generally well but mentions having occasional palpitations and a slight increase in the frequency of her bowel movements over the past few months. Her weight has been stable. Vital signs are temperature 37.1°C (98.8°F), blood pressure 128/78 mmHg, and pulse 96/min. Physical examination reveals a 1.6-cm, smooth, firm, and mobile nodule in the left lobe of the thyroid gland. No cervical lymphadenopathy is appreciated. A thyroid ultrasound confirms the presence of a 1.6-cm solid, hypoechoic nodule with regular margins in the left lobe, and no suspicious lymph nodes. Laboratory testing shows a serum thyroid-stimulating hormone (TSH) level of 0.05 µU/mL (normal: 0.4–4.0 µU/mL). Which of the following is the most appropriate next step in the management of this patient?

  1. A
    Fine-needle aspiration biopsy of the nodule
  2. Radionuclide thyroid scintigraphyAnswer
  3. C
    Measurement of anti-thyroid peroxidase antibodies
  4. D
    Administration of radioactive iodine (I-131)
  5. E
    Reassurance and repeat ultrasound in 6 months

Answer

Radionuclide thyroid scintigraphy
The patient presents with a palpable thyroid nodule and a suppressed TSH level. The initial workup of a thyroid nodule consists of a serum TSH measurement and a thyroid ultrasound. When the TSH is low, it indicates that the patient is hyperthyroid (either overtly or subclinically). In this scenario, the most appropriate next step is radionuclide thyroid scintigraphy (typically with Iodine-123 or Technetium-99m) to determine the functional status of the nodule. If the nodule is hyperfunctioning ('hot'), the risk of malignancy is extremely low, and the patient is evaluated and treated for hyperthyroidism (e.g., toxic adenoma). If the nodule is nonfunctioning ('cold'), there is a higher risk of malignancy, and fine-needle aspiration biopsy would be the subsequent step.

Step-by-Step Solution

1
Identify the primary clinical problem from the vignette.
The patient has a newly discovered 1.6-cm solid thyroid nodule, symptoms of mild hyperthyroidism (palpitations, increased bowel movements), and a suppressed serum TSH (0.05 µU/mL).
Establishing the constellation of physical and laboratory findings is essential to follow the correct diagnostic algorithm.
2
Determine the appropriate diagnostic algorithm for a thyroid nodule based on the TSH level.
Because the TSH is subnormal (suppressed), the next step is to evaluate the functional status of the nodule using radionuclide scintigraphy.
The initial evaluation of a thyroid nodule always includes a serum TSH and a thyroid ultrasound. A low TSH indicates overt or subclinical hyperthyroidism. Scintigraphy determines if the nodule is 'hot' (hyperfunctioning) or 'cold' (nonfunctioning).
3
Differentiate the indications for fine-needle aspiration (FNA) versus scintigraphy.
FNA is deferred at this stage because 'hot' nodules are very rarely malignant. If the scan shows a 'cold' nodule, FNA would then be indicated given its size (>1 cm).
Avoiding unnecessary biopsies is a key principle in the management of thyroid nodules; recognizing the proper sequence prevents procedural errors.

Key Concept

The initial workup of a thyroid nodule involves measuring serum TSH and performing an ultrasound. If the TSH is subnormal, radionuclide thyroid scintigraphy is the next best step to determine if the nodule is hyperfunctioning ('hot') or nonfunctioning ('cold').
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Topics

Endocrinology and Metabolism

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