IS Case 67: Grave's Disease/Diffuse Toxic Goiter
Imaging Sciences URMC 2008
Publication Date: 2009-05-19
History
Patient is a 67-year-old female with intermittent palpitations, weight loss and malaise. Laboratory results obtained 3 weeks prior to thyroid uptake and scan revealed the following elevated values: T3 294 ng/dl (normal 60-181), free T4 2.7 ng/dl (normal 0.9-1.8) and thyroid peroxidase antibody 581.4 IU/mL (normal 0-3.9). TSH was low at <0.01 uIU/mL (normal 0.35-5.50). Anti-thyroglobulin antibody was within normal limits at 8.2 IU/mL (normal 0-14.4).
Findings
Perfusion images demonstrate increased perfusion. Spot images demonstrate increased thyroid to salivary gland ratio. There is enlargement of the thyroid with increased radiotracer activity. A pyramidal lobe may be seen.
Diagnosis
Grave's Disease/Diffuse Toxic Goiter
Discussion
Graves' disease accounts for most cases of hyperthyroidism, especially in young and female patients. Graves' can cause ophthalmopathy and pretibial myxedema which are not seen with other causes of hyperthyroidism. General symptoms of hyperthyroidism are heat intolerance, weight loss, weakness, palpitations, oligomenorrhea, restlessness, insomnia, sweating, frequent bowel movements and anxiety. Signs of hyperthyroidism are brisk tendon reflexes, fine tremor, proximal weakness, fine hair, stare and eyelid lag.
Plasma TSH is the most useful first test with a TSH level of greater than 0.1 microU/ml excluding clinical hyperthyroidism. Plasma free T4 is usually elevated. Thyroid stimulating immunoglobulin antibody is positive in 80%. Antimicrosomal and antithyroglobulin antibodies as well as anti-nuclear antibodies (ANA) may be seen.
It typically manifests as thyromegaly with homogeneously increased radiotracer distribution throughout the thyroid. In many cases, a pyramidal lobe is present. On Tc-99m pertechnetate scan, the thyroid is increased in activity and the salivary glands are not well seen. Salivary glands are not normally seen on an I-123 scan so it can be difficult to differentiate Graves' disease from a normal study without knowing the uptake value. Twenty-four hour uptake values in Graves' disease are usually in the range of 40 to 70%. Cold nodules may be found in these patients, but carcinoma is very rare.
Beta blockers such as atenolol are used to relieve the symptoms of hyperthyroidism, such as palpitations, tremor and anxiety. Thioamides, such as methimazole and propylthiouracil, work by inhibiting thyroid hormone synthesis, having no permanent effect on thyroid function. Long-term control with thionamides is achieved in less than fifty percent of patients.
For definitive therapy, radioiodine treatment is most commonly used. Thyroidectomy is only used in patients refusing radioiodine treatment who relapse or develop side effects of drug treatment.
Prior to administering therapeutic I-131, the diagnosis of Graves' disease must be established by physical exam, history and laboratory work. An I-131 uptake is performed to rule out other etiologies such as silent, painless thyroiditis. Antithyroid medication should be stopper five to seven days before treatment. There is usually no noticeable improvement in symptoms until three to four weeks after treatment.
References
- Green GB, Harris IS, Lin GA, Moylan KC (Eds.). The Washington Manual of Medical Therapeutics. 31st ed., New York: Lippincott, Williams & Wilkins, 2004.
- Mettler FA, Guiberteau MJ. Essentials of Nuclear Medicine Imaging. 5th ed., Philadelphia: Sanders Elsevier, 2006.
- Sabatine MS (Ed.). Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine. 2nd ed., New York: Lippincott, Williams & Wilkins, 2004.
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