How should a patient with a history of thyroid nodules and low TSH be managed?

Management of Thyroid Nodules with Low-Normal TSH

In this patient with thyroid nodules and a low-normal TSH (0.330), you should proceed with high-resolution thyroid ultrasound to characterize the nodules and determine if fine-needle aspiration is indicated based on size and sonographic features. 1, 2

Initial Diagnostic Pathway

Measure serum TSH first (already done) as it determines the subsequent diagnostic pathway and is the single best initial test of thyroid function. 2 Your patient's TSH of 0.330 mIU/L is at the lower end of normal but not suppressed, which means:

• Do not proceed to radioiodine uptake scan - this is only indicated when TSH is frankly suppressed/low, as hyperfunctioning "hot" nodules are rarely malignant and don't require FNA. 2
• Proceed directly to ultrasound-guided evaluation without radionuclide scanning since TSH is within normal range. 2

The free T3 (3.1) and T4 (1.22) are normal, confirming euthyroid status. 3

Ultrasound Evaluation Strategy

Perform high-resolution thyroid ultrasound of the thyroid and central neck to characterize all nodules. 2 Ultrasound can detect nodules as small as 5mm and is the only appropriate initial imaging study for thyroid nodule characterization. 1

Suspicious Ultrasound Features Requiring FNA:

Look specifically for these malignancy-associated features: 1, 2

• Microcalcifications (highly specific for papillary thyroid carcinoma)
• Marked hypoechogenicity (solid nodules darker than surrounding thyroid)
• Irregular or microlobulated margins (infiltrative borders)
• Absence of peripheral halo
• Central hypervascularity (chaotic internal vascular pattern)
• Taller-than-wide shape

FNA Decision Algorithm:

Proceed with ultrasound-guided FNA when: 1, 4

• Any nodule >1 cm with ≥2 suspicious ultrasound features
• Any nodule <1 cm with suspicious features PLUS high-risk clinical factors (see below)
• Any nodule >4 cm regardless of ultrasound appearance
• Suspicious cervical lymphadenopathy present

Important caveat: For nodules ≤10 mm diameter, FNA should only be considered when suspicious US signs are present. Nodules ≤5 mm should be monitored rather than biopsied. 4

High-Risk Clinical Features Assessment

Evaluate for these factors that lower the threshold for FNA: 2

• History of head and neck irradiation
• Family history of thyroid cancer or associated syndromes (MEN 2A/2B, familial adenomatous polyposis, Carney complex, Cowden's syndrome)
• Age <15 years or male gender
• Nodule that is firm, fixed, or rapidly growing
• Vocal cord paralysis or symptoms of invasion

Additional Diagnostic Considerations

Do not routinely measure serum calcitonin in all patients with thyroid nodules, as this remains controversial and cost-effectiveness is not established in the United States. 2 However, it may be considered if there are specific concerns for medullary thyroid carcinoma. 1

Follow-Up Strategy if FNA Not Indicated

If ultrasound shows benign features without indication for immediate FNA: 2

• Initial follow-up at 1,3,6, and 12 months during the first year
• After 12 months, annual ultrasound for benign nodules
• Repeat FNA if nodule increases by ≥3 mm in any dimension or develops new suspicious features
• Low-risk patients with nodules <6 mm without suspicious features may not require routine follow-up

Critical Pitfall to Avoid

Do not rely on thyroid function tests (TSH, T3, T4) for malignancy assessment, as most thyroid cancers present with normal thyroid function. 1 The slightly low-normal TSH does not exclude malignancy and should not provide false reassurance. The decision for FNA is based on ultrasound characteristics and nodule size, not thyroid function. 2, 3