Hyperthyroid Disorders

Lesson 5: Diagnosing Hyperthyroidism

Imaging Tests

Several imaging tests are available to help diagnose the specific cause of hyperthyroidism. Imaging tests, which include X-rays and more sophisticated techniques, are the procedures performed in the radiology department.

The RAI-Uptake Test At one time the RAI-Uptake Test and Scan was the only procedure available to help determine the cause of hyperthyroidism. In this test, the patient is given an oral dose of radioiodine usually in the form of I-123. Sometimes technetium or I-131 are used.

At 6 or 24 hours after the dose is administered, the amount of residual radioiodine is measured. The thyroid gland is also scanned at this time to determine the pattern of uptake. Areas that take up less or more radioiodine than the surrounding tissue represent nodules. In Graves’ disease, hereditary hyperthyroidism and thyroiditis, the scan is diffuse or even with all the cells taking up the same amount of radioiodine.

In patients with thyroid nodules and Graves’ disease, the uptake is generally elevated. At 24 hours, patients with mild disease usually have an uptake as high as 60 percent. In patients with thyroiditis, the uptake is low. Excess dietary iodine can falsely decrease the uptake results. Medications with high concentrations of iodine, such as amiodarone, and iodine contrast dyes can falsely decrease the results for several months. The dose of radioiodine used in the uptake is much lower than that used for ablation. Still, radioiodine remains in the blood circulation for several days. Results can suggest Graves’ disease but can’t distinguish between Graves’ disease and hereditary hyperthyroidism. A blood test for TSI can be used to definitively diagnose Graves’ disease.

Ultrasonography
Ultrasonagraphy offers the benefits of a thyroid scan and the advantage that it’s not an invasive procedure. Ultrasound is very sensitive for detecting thyroid lesions and for distinguishing nodules from cysts. Like the thyroid scan, ultrasonography cannot distinguish benign from malignant masses. For this a fine needle aspiration biopsy is needed. Ultrasound can easily determine thyroid volume. A reduction in volume shows a good response to anti-thyroid drug therapy in subsequent ultrasounds.

Cat Scans
Computed tomography can also be used to distinguish nodules and help diagnose Graves’ disease. This procedure is more expensive and not generally used unless the position of the gland in relation to other organs needs to be determined.

MRI
In magnetic resonance imaging, the thyroid can be studied and the amount of fat to muscle can be determined. The vascularity of the thyroid gland can also be studied. This procedure is not routinely used to determine the cause of hyperthyroidism although it can be used to show the degree of gland enlargement and any involvement of adjacent organs.

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