Preliminary Diagnosis: Graves’ Disease
I. What imaging technique is first-line for this diagnosis
- Thyroid scan (thyroid scintigraphy)
II. Describe the advantages and disadvantages of this technique for diagnosis of Graves’ disease.
Advantages
- Can help differentiate other causes of thyrotoxicosis, such as functional thyroid nodules
- Can support the diagnosis of Graves’ disease
- After the thyroid scan is performed, further treatment with radioactive iodine may proceed
Disadvantages
- Uses radioactive pharmaceuticals
- Relatively lengthy procedure
III. What are the contraindications for the first-line imaging technique?
- Pregnancy
- Breast-feeding women
- Recent (8 weeks) intravenous administration of iodine-based contrast (relative)
- Failure to discontinue thyroid medication
IV. What alternative imaging techniques are available?
- Ultrasound
- Contrast enhanced CT of the orbits.
- Contrast enhanced MRI of the orbits.
V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of Graves’ disease.
Ultrasound
Advantages
- Characteristic findings of Graves’ disease can support the diagnosis. However, specificity is diminished.
- Characterization of thyroid nodules is identified on a thyroid scan.
- Ultrasound guided fine needle aspiration of suspicious thyroid nodules can be performed.
Disadvantages
- Imaging findings are not specific for Graves’ disease.
Contrast enhanced CT of the orbits
Advantages
- Indicated in cases of suspected thyroid ophthalmopathy
Disadvantages
- Uses ionizing radiation
- Cost.
Contrast Enhanced MRI of the orbits
Advantages
- Indicated in cases of suspected thyroid ophthalmopathy
Disadvantages
- Cost
VI. What are the contraindications for the alternative imaging techniques?
Ultrasound
- None
Contrast enhanced CT of the orbits
- Pregnancy (relative)
- Anaphylactoid reaction to iodinated contrast; steroid preparation may be used in patients with mild or moderate allergic reactions.
Contrast enhanced MRI of the orbits
- Non-MRI compatible implanted devices
- Relative contraindications include claustrophobia, obesity (due to MRI weight limits), and metallic implants in region of interest that are not MRI compatible
- Renal dysfunction; use of gadolinium contraindicated when glomerular filtration rate is less than 30
- Allergy to gadolinium contrast agents
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