Differential Diagnosis for a Solitary Thyroid Nodule with Radioactive Iodine Uptake

• Single most likely diagnosis
  • Toxic Adenoma: This is the most likely diagnosis because a solitary thyroid nodule that takes up radioactive iodine suggests a functioning adenoma, which can produce thyroid hormones independently of the normal thyroid tissue, leading to hyperthyroidism.
• Other Likely diagnoses
  • Follicular Adenoma: Although less likely to be functional (take up iodine) than a toxic adenoma, some follicular adenomas can have varying degrees of iodine uptake, making them a consideration.
  • Hyperfunctioning Thyroid Nodule: Essentially synonymous with a toxic adenoma, this term emphasizes the nodule's ability to produce excess thyroid hormone.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Papillary Thyroid Carcinoma: Although thyroid cancers are generally cold (do not take up iodine) on scintiscan, a small percentage can be functional. Missing a diagnosis of thyroid cancer could have significant consequences.
  • Follicular Thyroid Carcinoma: Similar to papillary carcinoma, most follicular carcinomas are cold, but the rare ones that take up iodine must be considered to avoid missing a malignant diagnosis.
• Rare diagnoses
  • Thyroid Metastasis: Rarely, a metastasis from another cancer can mimic a thyroid nodule and, even more rarely, take up iodine.
  • Thyroid Hyperplastic Nodule: In the context of a multinodular goiter, a single nodule might be hyperfunctioning, but this would typically be part of a larger gland with multiple nodules rather than a solitary finding.