Do patients with a known thyroid nodule being treated with Methimazole (methimazole) for hyperthyroidism still require regular ultrasound (US) head and neck scans to monitor the nodule for at least 5 years?

Thyroid Nodule Surveillance During Methimazole Treatment

Yes, you should continue ultrasound surveillance of the thyroid nodule according to standard thyroid nodule guidelines, independent of methimazole treatment for hyperthyroidism. Methimazole treats the hyperthyroidism but does not eliminate malignancy risk in coexisting nodules.

Key Principle: Separate the Two Conditions

• Hyperthyroidism and thyroid nodules are distinct clinical entities that require independent evaluation and monitoring 1, 2, 3
• The presence of hyperthyroidism requiring methimazole does not reduce the malignancy risk of a coexisting thyroid nodule 4
• Ultrasound surveillance ensures that suspicious nodules concerning for cancer are not overlooked, even in patients being treated for hyperthyroidism 3

Initial Evaluation Algorithm

• All thyroid nodules should first be evaluated with TSH measurement, followed by ultrasound 2, 3
• If TSH is low (as expected in untreated hyperthyroidism), perform ultrasound first to evaluate thyroid morphology and characterize the nodule, then follow with radioiodine uptake scan to determine if the nodule is hyperfunctioning 2, 3
• Hyperfunctioning ("hot") nodules on uptake scan rarely require biopsy due to very low malignancy risk, but this must be confirmed with scintigraphy 2, 3
• If the nodule is "cold" (non-functioning) on uptake scan, standard nodule surveillance and biopsy criteria apply regardless of hyperthyroidism treatment 2

Surveillance Protocol for Thyroid Nodules

• For nodules ≥1 cm or smaller nodules with suspicious ultrasound features, fine-needle aspiration biopsy (FNAB) should be performed 2, 3
• Suspicious ultrasound features include: hypoechogenicity, microcalcifications, irregular or microlobulated margins, absence of peripheral halo, solid composition, intranodular blood flow, and taller-than-wide shape 2, 5
• For benign nodules (Bethesda category II), continued surveillance is appropriate with repeat ultrasound at intervals determined by initial risk stratification 2

Critical Pitfall to Avoid

• Do not assume that methimazole treatment or the presence of hyperthyroidism eliminates the need for nodule surveillance 1, 3
• Coexisting thyroid nodules requiring biopsy for malignancy evaluation can be missed if ultrasound evaluation is skipped 1
• Even in patients with Graves disease or toxic nodules, papillary thyroid carcinoma can coexist and requires detection 6

Practical Approach During Methimazole Treatment

• Perform baseline ultrasound of the thyroid and neck (including cervical lymph nodes) to fully characterize the nodule 3
• If the nodule meets criteria for FNAB based on size (≥1 cm) or suspicious features, proceed with biopsy regardless of hyperthyroid status 2, 3
• Continue standard nodule surveillance protocols for at least 5 years based on initial risk stratification and cytology results 7
• The methimazole treatment timeline and the nodule surveillance timeline run in parallel but are managed independently 4