Toxic Thyroid Adenoma

A toxic thyroid adenoma is a benign autonomous thyroid nodule that produces excess thyroid hormone independently of TSH control. It usually causes T3/T4 thyrotoxicosis with a suppressed TSH, and is more common in older adults than Graves’ disease.

🧠 Pathophysiology

• A single thyroid nodule becomes autonomous and secretes thyroid hormone without normal pituitary regulation.
• High T3/T4 suppresses pituitary TSH, so the surrounding normal thyroid tissue becomes relatively inactive.
• On radionuclide scanning, the adenoma is typically a “hot nodule” with reduced uptake in the rest of the gland.
• Unlike Graves’ disease, it is not usually autoimmune, so eye signs and TSH receptor antibodies are usually absent.

⚠️ Clinical Features

• Palpitations, tremor, heat intolerance, sweating and weight loss.
• Anxiety, insomnia, proximal muscle weakness or fatigue.
• Atrial fibrillation, worsening angina or heart failure in older patients.
• Single palpable thyroid nodule, often with no bruit and no Graves’ orbitopathy.
• Large nodules may cause local symptoms such as dysphagia, cough, dyspnoea or voice change.

🧪 Investigations

• Thyroid function tests: suppressed TSH with raised free T4 and/or free T3.
• T3-toxicosis: T3 may be raised before T4, so check free T3 if TSH is suppressed.
• TSH receptor antibodies: usually negative; useful if Graves’ disease is a differential.
• Thyroid ultrasound: assesses nodule size, structure and suspicious features.
• Radionuclide thyroid scan: shows a solitary hyperfunctioning “hot” nodule with suppression of background uptake.
• ECG: consider in older patients or those with palpitations to look for atrial fibrillation.

🚩 Red Flags

• Rapidly enlarging nodule.
• Hard, fixed or irregular thyroid mass.
• Cervical lymphadenopathy.
• Hoarseness or vocal cord palsy.
• Stridor, dyspnoea, dysphagia or symptoms of tracheal compression.
• Previous neck irradiation or strong family history of thyroid cancer.

💊 Initial Management

• Refer to endocrinology for confirmation and definitive management.
• Beta-blocker: propranolol may be used for tremor, palpitations and adrenergic symptoms if not contraindicated.
• Carbimazole: may control thyrotoxicosis before definitive treatment, but it does not usually cure toxic adenoma.
• Before antithyroid drugs, check FBC and LFTs, and warn about sore throat, fever, mouth ulcers or jaundice.

🏥 Definitive Treatment

• Radioactive iodine: first-line definitive option if suitable; destroys overactive thyroid tissue.
• Surgery: usually hemithyroidectomy/lobectomy for a solitary toxic adenoma, especially if large, compressive, suspicious, or radioiodine is unsuitable.
• Long-term antithyroid drugs: an option if radioactive iodine and surgery are unsuitable.
• Monitor for hypothyroidism after definitive treatment and replace with levothyroxine if required.

👶 Pregnancy

• Radioactive iodine is contraindicated in pregnancy and breastfeeding.
• Specialist endocrine and obstetric input is required if thyrotoxicosis occurs during pregnancy.
• Use antithyroid medication only with specialist advice because treatment choice depends on gestation and risk profile.

🧾 Differentials

• Graves’ disease: diffuse goitre, orbitopathy, positive TSH receptor antibodies.
• Toxic multinodular goitre: multiple autonomous nodules, usually in older adults.
• Thyroiditis: transient thyrotoxicosis from hormone leakage, often low uptake on radionuclide scan.
• Exogenous thyroid hormone: suppressed TSH from over-replacement or surreptitious use.

📌 Key Points

• Toxic adenoma is a single autonomous hot nodule causing hyperthyroidism.
• It is usually not autoimmune, so Graves’ eye signs are absent.
• Carbimazole can control hormone excess but is rarely definitive.
• NICE recommends radioactive iodine or surgery as first-line definitive treatment for adults with hyperthyroidism due to a single nodule, with life-long antithyroid drugs if these are unsuitable.