Case Author(s): Tate Allen, M.D. and Tom R. Miller, M.D., Ph.D. , 8/30/98 . Rating: #D3, #Q4

Diagnosis: Subacute Thyroiditis

Brief history:

51-year-old female with hyperthyroidism

View second image(tr). Thyroid Scintigraphy with Tc-99m Pertechnetate. I-131 uptake (worksheet not shown) was 0.2%

Full history/Diagnosis is available below

Diagnosis: Subacute Thyroiditis

Full history:

This patient was well until one month ago when she developed fatique, weight loss, decreased appetite, fevers and neck pain with swallowing. The patient has no eye symptoms. On physical examination, the patient has an increased heart rate, warm skin, and fine hair. The thyroid is not enlarged. The patient's free serum T4 was 3.4 ng/dl (normal range 0.8-1.8 ng/dl) and the serum TSH was less than 0.01 uU/ml (normal range 0.4-5.5 uU/ml).

Radiopharmaceutical:

5.0 uCi I-131 sodium iodide p.o. and 5.0 mCi Tc-99m Pertechnetate i.v.

Findings:

The 24-hour I-131 uptake is 0.2% (normal range 10-30%). After checking with the technologist and the patient, it was confirmed that she recieved the I-131 dose. Thyroid scintigraphy was performed. There is no thyroid uptake.

Discussion:

Subacute thyroiditis is thought to be caused by a virus. In the active phase, the inflammatory process causes a "dumping" of thyroid hormone into the circulation. The clinical picture and thyroid function tests can be mistaken for Graves' disease. However, the I-131 uptake usually is low. Later, during recovery, the symptoms will subside and the thyroid hormone level may be low. At that time the TSH level will be elevated.

Reference: Thrall J, Ziessman H: Nuclear Medicine The Requisites. St. Louis, Mosby, 1995.

Major teaching point(s):

Subacute thyroiditis should not be mistaken for Graves' disease in patient referred for radioactive iodine therapy. This two entities, which may have identical clinical and laboratory presentations, are distinguished by the 24-hour radioactive iodine uptake. Indeed, that is the primary purpose of the uptake measurment, with calculation of dose the important but secondary reason for soing the test.

ACR Codes and Keywords:

References and General Discussion of Thyroid Scintigraphy (Anatomic field:Face, Mastoids, and Neck, Category:Inflammation,Infection)

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Case number: tr007

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