What is the next step in evaluating a patient with a swollen and enlarged thyroid gland, particularly those with a history of hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid)?

Next Step: Thyroid Ultrasound

When you find a swollen and enlarged thyroid gland on physical examination, the next step is to obtain a thyroid ultrasound to characterize the structural abnormality, regardless of whether the patient has a history of hypothyroidism or hyperthyroidism. 1

Initial Laboratory Assessment

Before or concurrent with imaging, measure serum TSH as the primary screening test for thyroid dysfunction 1:

• TSH is the most sensitive test for detecting thyroid dysfunction, with sensitivity above 98% and specificity greater than 92% 2, 3
• If TSH is abnormal, measure free T4 to distinguish between subclinical (normal free T4) and overt (abnormal free T4) dysfunction 2, 3
• For patients with known hypothyroidism or hyperthyroidism, TSH and free T4 help assess current disease control 2

Role of Thyroid Ultrasound

Ultrasound is the routine preoperative and diagnostic study for all patients with thyroid enlargement (goiter) 1:

• Ultrasound evaluates for thyroid nodules, which are the most common finding in enlarged thyroid glands 1
• It distinguishes between diffuse enlargement (as in Graves' disease or Hashimoto's thyroiditis) versus nodular goiter 1
• Ultrasound can assess for extrathyroidal invasion and identify lymph nodes in the lateral compartment >8-10 mm 1
• On Doppler ultrasound, increased thyroid blood flow suggests hyperthyroidism from Graves' disease or toxic adenoma, while decreased flow suggests destructive thyroiditis 1

When Additional Imaging Is NOT Indicated

There is no role for CT, MRI, or radionuclide imaging in the initial workup of hypothyroidism in adults 1:

• Imaging for thyroid morphology does not help differentiate among causes of hypothyroidism 1
• All causes of hypothyroidism will have decreased radioiodine uptake 1
• FDG-PET/CT has no role in hypothyroidism workup 1

When Radionuclide Uptake Study IS Indicated

If the patient presents with clinical hyperthyroidism (thyrotoxicosis), a radionuclide uptake study is preferred to distinguish between true hyperthyroidism (Graves' disease, toxic adenoma) and destructive thyroiditis 1, 4, 5:

• Radionuclide uptake directly measures thyroid activity rather than inferring it based on blood flow 1
• High uptake indicates Graves' disease or toxic nodular goiter 4, 5
• Low or absent uptake indicates thyroiditis, factitious hyperthyroidism, or iodine-induced thyrotoxicosis 4, 5

Additional Diagnostic Tests to Consider

• Measure anti-TPO antibodies if autoimmune thyroid disease (Hashimoto's or Graves') is suspected, as this confirms autoimmune etiology and predicts progression risk 2, 6
• Measure TSH-receptor antibodies (TBII or TRAb) if Graves' disease is suspected clinically 5, 7, 8
• Fine needle aspiration biopsy (FNA) is indicated if ultrasound identifies suspicious thyroid nodules requiring cytologic evaluation 1, 8

Common Pitfalls to Avoid

• Do not order CT or MRI for initial evaluation of goiter unless there is concern for substernal extension or compressive symptoms requiring surgical planning 1
• Do not delay ultrasound while waiting for thyroid function tests to return—these can be done concurrently 1
• Do not assume the goiter is benign without ultrasound evaluation, as 20% of patients with thyroid cancer have additional sites of disease not appreciated on physical examination 1
• Avoid using iodinated contrast CT in patients with suspected hyperthyroidism, as this can precipitate thyroid storm or delay radioiodine therapy 1