Thyroid Radionuclide Scan

Indications

• When clinical presentation and laboratory tests cannot differentiate causes of thyrotoxicosis (e.g., when TSH receptor antibodies are negative, ~10% of cases)

• Evaluate thyroid nodules to assess "cold" or "hot" nodules

• Suspected hyperthyroidism with goitre

• Assessing the functional status of thyroid nodules in patients with a subnormal TSH

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Pathologies Detected

• Toxic Adenoma: Focal increased uptake

• Toxic Multinodular Goitre: Multiple focal increased uptake areas

• Graves' Disease: Diffuse increased uptake

• Subacute Thyroiditis: Decreased or absent uptake

• Drug-Induced Thyroiditis: Decreased or absent uptake

• Autonomous Nodule: Intense focal uptake with suppression of surrounding thyroid tissue.

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Contraindications

• Pregnancy.

• Breastfeeding (should discontinue breastfeeding for 24–48 hours post-scan)

• Recent exposure to iodine-containing contrast agents or medications (e.g., amiodarone) may affect scan results

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Patient Preparation

• Inform patients about the procedure, including the need for an intravenous injection and the duration of the scan (45–60 minutes)

• Advise patients to remove neck jewellery and wear clothing that allows easy access to the arm for injection

• Discuss potential radiation exposure and ensure women of childbearing age are assessed for pregnancy or breastfeeding status

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Medications and Substances Affecting Scan Results

• Water-soluble intravenous contrast agents (used in CT scans)

• Amiodarone

• Thyroxine or liothyronine (Tertroxin)

• Some mineral/vitamin supplements containing iodine

• Patients should discontinue these substances for an appropriate period before the scan to minimise the risk of a nondiagnostic result

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Interpretation of Results

• The pattern of radionuclide uptake helps differentiate causes of hyperthyroidism, guiding treatment decisions

• Functioning ("hot") nodules in hyperthyroid patients typically lead to treatment of hyperthyroidism

• Non-functioning ("cold") nodules may require further investigation, such as ultrasound and/or fine-needle biopsy, due to a higher risk of malignancy