What is the appropriate next step in management for a patient with a focal hot nodule in the right lower pole of the thyroid, normal gland size, borderline‑high 24‑hour radionuclide uptake, suppressed TSH and normal free T4 (subclinical hyperthyroidism)?

Management of Focal Hot Nodule with Subclinical Hyperthyroidism

You should initiate methimazole as bridge therapy and proceed with definitive treatment using either radioactive iodine ablation or surgery, with the choice depending on nodule size, patient age, and presence of compressive symptoms. 1

Immediate Next Steps

Confirm the Diagnosis and Assess Severity

• Measure free T3 levels immediately to distinguish true subclinical hyperthyroidism from overt "free T3 toxicosis"—patients with suppressed TSH and normal free T4 may still have elevated free T3, which represents overt hyperthyroidism requiring more aggressive treatment. 2
• Your patient has TSH 0.01 mIU/L (suppressed) with normal free T4 (1.7 ng/dL), but without knowing the free T3 level, you cannot definitively classify this as subclinical versus overt hyperthyroidism. 2
• The borderline-elevated 24-hour uptake (29%, just above normal range of 4-27%) with focal increased uptake in the right lower pole confirms an autonomously functioning thyroid nodule (toxic adenoma). 1

Obtain Thyroid Ultrasound with Focused Evaluation

• Request the outside thyroid ultrasound images for direct review to evaluate the size of the hot nodule and assess for any suspicious features in other areas of the thyroid. 3
• If any nodules appear "cold" on the radionuclide scan or have suspicious ultrasound features (hypoechogenicity, microcalcifications, irregular borders), perform fine needle aspiration biopsy—while hot nodules are rarely malignant, coexisting cold nodules require evaluation. 3, 4
• The radionuclide scan report states "no apparent cold nodule," but direct correlation with ultrasound is essential since approximately 5-10% of thyroid nodules harbor malignancy. 3

Treatment Algorithm Based on Clinical Factors

Initiate Medical Management First

• Start methimazole immediately to control hyperthyroidism while preparing for definitive therapy—this serves as bridge therapy before surgery or radioactive iodine and reduces cardiac risks, particularly atrial fibrillation in older patients. 1
• Monitor for agranulocytosis, particularly in the first 3 months of methimazole therapy. 1

Choose Definitive Treatment Based on These Criteria:

Select Surgery (Total or Near-Total Thyroidectomy) if:

• The hot nodule is large (>3-4 cm) with compressive symptoms (dyspnea, dysphagia, dysphonia, orthopnea). 1, 5
• Patient is young with long life expectancy—surgery provides immediate cure without radiation exposure. 1
• Any nodules require histological evaluation due to suspicious ultrasound features. 1
• CT neck without contrast shows substernal extension or significant tracheal compression. 1
• In expert hands, complications (laryngeal nerve palsy, hypoparathyroidism) occur in <1-2% of cases. 1

Select Radioactive Iodine (I-131) if:

• Patient is elderly or has significant surgical comorbidities making anesthesia high-risk. 1
• Smaller nodule without compressive symptoms and patient preference to avoid surgery. 1
• Typical dose for toxic nodular goiter is 10-15 mCi (higher than the 4-10 mCi used for diffuse Graves' disease). 6
• Avoid iodinated contrast agents before RAI—they interfere with iodine uptake for 4-8 weeks. 3

Critical Decision Point: Treat or Observe?

You should treat this patient definitively rather than observe because:

• TSH is profoundly suppressed (<0.1 mIU/L), not just mildly low. 3, 7
• Patients with undetectable TSH (<0.1 mIU/L) have significantly higher risk of atrial fibrillation, heart failure, osteoporosis, and increased mortality compared to those with TSH 0.1-0.4 mIU/L. 3, 5
• Treatment is recommended for subclinical hyperthyroidism when TSH <0.1 mIU/L, especially in patients over age 65 or with cardiovascular risk factors. 3, 5
• The majority (66%) of thyroid specialists favor treating older patients with undetectable TSH, even when free T4 is normal. 7

Post-Treatment Monitoring

After Radioactive Iodine:

• Monitor thyroid function tests every 4-6 weeks initially, then every 3-6 months. 1
• Initiate levothyroxine replacement if hypothyroidism develops—this occurs in the majority of patients treated with RAI for toxic nodules. 1

After Surgery:

• Initiate levothyroxine replacement immediately postoperatively after total thyroidectomy. 1
• Monitor calcium levels closely for hypoparathyroidism, particularly in the first 48 hours. 1

Important Pitfalls to Avoid

• Do not delay definitive treatment in elderly patients—cardiac complications from untreated subclinical hyperthyroidism, particularly atrial fibrillation, carry significant morbidity and mortality. 1, 5
• Do not assume all hot nodules are benign—while rare, papillary thyroid carcinoma can occur in hyperfunctioning nodules, so correlate radionuclide findings with ultrasound features. 4
• Do not confuse this with central hypothyroidism—the suppressed TSH with normal-low free T4 could theoretically represent pituitary failure, but the hot nodule on scan confirms primary thyroid autonomy. 8
• Do not rely solely on TSH and free T4—measure free T3 to determine true disease severity, as some patients have isolated T3 toxicosis requiring more aggressive treatment. 2