A 36-year-old woman comes to the clinic for evaluation of a neck mass. She noticed a lump … — USMLE Step 2 CK

A 36-year-old woman comes to the clinic for evaluation of a neck mass. She noticed a lump on the right side of her neck 3 weeks ago while applying lotion. She feels occasionally warm and has had mild palpitations recently, but she attributes these symptoms to stress at work. Her menstrual cycles are regular. Vital signs show a heart rate of $98/\text{min}$ and blood pressure of $128/78\text{ mmHg}$ . Physical examination reveals a firm, mobile, $2.4\text{-cm}$ nodule in the right lobe of the thyroid gland. No cervical lymphadenopathy is appreciated.

Laboratory studies reveal the following:

Laboratory Test	Result	Reference Range
Thyroid-stimulating hormone (TSH)	$0.05 \text{ mU/L}$	$0.4–4.0 \text{ mU/L}$
Free thyroxine (T4)	$1.9 \text{ ng/dL}$	$0.9–2.4 \text{ ng/dL}$

Ultrasound of the neck shows a $2.4\text{-cm}$ solid, hypoechoic nodule in the right lobe with smooth margins and no microcalcifications.

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

A
Fine-needle aspiration biopsy of the nodule
B
Right hemithyroidectomy
Radionuclide thyroid scintigraphyAnswer
D
Measurement of serum calcitonin level
E
Measurement of serum thyroglobulin level

Answer

The correct answer is radionuclide thyroid scintigraphy.

The correct answer identifies that the initial diagnostic algorithm for a palpable thyroid nodule depends heavily on the TSH level. Because this patient's TSH is subnormal (indicating possible hyperthyroidism or an autonomously functioning nodule), a radionuclide thyroid scan (scintigraphy) must be performed next. If the scan shows increased uptake in the nodule ('hot' nodule), it is almost certainly benign and fine-needle aspiration (FNA) is not needed. If it shows decreased uptake ('cold' nodule), an FNA is indicated to rule out malignancy.

Step-by-Step Solution

Analyze the clinical presentation and initial laboratory findings.

The patient has a 2.4-cm solid thyroid nodule, a suppressed TSH level (0.05 mU/L), and normal free T4.

The initial evaluation of any thyroid nodule requires measuring TSH and performing a thyroid ultrasound to establish the functional status and sonographic risk.

Determine the diagnostic pathway based on the TSH level.

The suppressed TSH indicates that the nodule may be autonomously producing thyroid hormone, which alters the standard diagnostic algorithm.

If the TSH is normal or elevated, the next step is fine-needle aspiration (FNA) based on size and sonographic features. A low TSH requires functional imaging first.

Select the appropriate imaging modality for a patient with a nodule and a low TSH.

Radionuclide thyroid scintigraphy is the most appropriate next step.

Scintigraphy distinguishes between a 'hot' (hyperfunctioning) nodule and a 'cold' (nonfunctioning) nodule. Hyperfunctioning nodules are rarely malignant, whereas 'cold' nodules require an FNA biopsy.

Key Concept

In the evaluation of a thyroid nodule, if the initial TSH is subnormal, a radionuclide thyroid scan is the required next step to determine if the nodule is autonomously functioning.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic