What is the best management for a patient with a 2x2 cm thyroid nodule, severe hyperthyroidism (low Thyroid Stimulating Hormone (TSH), high Triiodothyronine (T3) and high Thyroxine (T4))?

Management of Hyperfunctioning Thyroid Nodule with Biochemical Hyperthyroidism

Radioactive iodine therapy is the preferred definitive treatment for this patient with a 2x2 cm toxic thyroid adenoma causing biochemical hyperthyroidism. 1

Initial Medical Management

Before definitive therapy, antithyroid drugs should be initiated to achieve a euthyroid state and prevent thyroid storm during treatment. 1

• Start methimazole as the initial medical management to control hyperthyroidism prior to definitive therapy. 1
• Methimazole inhibits thyroid hormone synthesis but does not inactivate existing circulating thyroid hormones, so clinical improvement takes time. 2
• Monitor thyroid function tests periodically during therapy, and once clinical hyperthyroidism resolves with rising TSH, reduce the methimazole dose. 2
• Patients should be under close surveillance and report immediately any evidence of illness, particularly sore throat, fever, or general malaise, as agranulocytosis occurs in 0.1-0.5% of patients. 2, 3

Definitive Treatment Selection

Radioactive iodine (RAI) is the treatment of choice for this patient based on nodule size and clinical presentation. 1

• For autonomously functioning nodules ≤3 cm (this patient has a 2x2 cm nodule), a standard 10 mCi dose of I-131 achieves complete cure in the majority of cases within 6 months, with only a 10% failure rate. 1
• RAI therapy provides definitive treatment without the surgical risks and is highly effective for toxic adenomas of this size. 1

Why Surgery Is Not the Best Option

• Hemithyroidectomy (Option C) is not preferred because RAI offers equivalent efficacy with lower morbidity for nodules of this size. 1
• Total thyroidectomy (Option D) is inappropriate for unilateral toxic adenoma and is reserved for bilateral toxic multinodular goiter or when malignancy is suspected. 1
• Surgery carries risks of hypoparathyroidism, recurrent laryngeal nerve injury, and requires general anesthesia. 1

Why Antithyroid Drugs Alone Are Insufficient

• Antithyroid drugs alone (Option A) are not definitive treatment and serve only as initial medical management to achieve euthyroid state prior to definitive therapy. 1
• Long-term continuous methimazole treatment requires indefinite medication use with ongoing monitoring and carries a 3-5% risk of adverse effects, including the life-threatening complication of agranulocytosis. 3
• Toxic adenomas are autonomous and do not remit with medical therapy alone, unlike Graves' disease where remission is possible. 1

Alternative Treatment Consideration

• Percutaneous ethanol injection (PEI) represents an alternative for patients refusing RAI or surgery, achieving complete cure in 78% of toxic adenomas with minimal complications. 1
• However, PEI is not listed among the answer choices and remains a second-line option when standard treatments are refused or contraindicated. 1, 4

Critical Management Points

• Never confuse this with central hyperthyroidism, which would show elevated or inappropriately normal TSH with elevated T3/T4 (from TSH-producing pituitary tumors or pituitary resistance to thyroid hormone). 5
• In this patient, the very low TSH with high T3/T4 confirms primary hyperthyroidism from autonomous nodule function, not central causes. 5
• The nodule size of 2x2 cm is ideal for RAI therapy, as nodules >40 ml may have reduced response rates, though this patient's nodule is well below that threshold. 4

Monitoring After RAI Treatment

• Following RAI therapy, monitor for development of hypothyroidism, which may require levothyroxine replacement. 1
• Thyroid function should be assessed at 6 weeks, 3 months, and 6 months post-treatment to evaluate response and detect hypothyroidism. 1

Answer: B. Radioactive iodine 1