II. Indications

  1. Hyperthyroidism diagnosis and management

III. Mechanism

  1. Iodine-123 (I-123) uptake by the Thyroid Gland is measured
  2. Typical uptake is 15-25% in 24 hours

IV. Causes: Diffusely Low radioidoine uptake with hyperthyrodism

  1. Medications and other intakes
    1. Exogenous Thyroid intake
    2. Excessive exogenous Iodine
    3. Amiodarone
  2. Transient Thyroiditis
    1. Subacute Thyroiditis
    2. Postpartum Thyroiditis (5-8% Incidence)
    3. Painless lymphocytic Thyroiditis

V. Causes: Focal low RAIU (cold Nodule) with Hypothyroidism

  1. Requires biopsy for Thyroid Cancer evaluation

VI. Causes: High Radioiodine Uptake with Hyperthyroidism

  1. Diffusely increased uptake
    1. Thyrotoxicosis (e.g. Grave's Disease)
  2. Localized increased uptake (Hot Nodule)
    1. Hyperfuntioning Thyroid Nodule

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