Findings: Following the oral administration of 400 microcuries of iodine 123 sodium iodide, anterior images over the neck were performed at 24 hours. This demonstrates an enlarged right lobe with an oval-shaped hot focus. The left lobe is of normal configuration but with marked suppression. Biochemical markers demonstrate that the patient is mildly hyperthyroid.

Diagnosis: Plummer's disease.

Discussion: Plummer's disease is marked by an autonomous nodule which is usually a hyperfunctioning adenoma. As in this case, the autonomous nodule suppresses the remainder of the thyroid gland. Higher doses of iodine 131 are used for treatment than with Grave's disease. The goal is to knock out the autonomous nodule which can be somewhat resistant to therapy.

Autonomous nodules produce enough thyroid hormone to suppress TSH secretion and hence, suppress the remaining normal thyroid tissue.

Most hot nodules are benign and are usually hyperfunctioning adenomas. Less than 1% of hot nodules represent carcinoma.

References:
Becker DV, Hurley JR: Radioiodine Treatment of Hyperthyroidism.
In: Sandler MP, Coleman RE, Wackers FJ, et al. (Eds): Diagnostic Nuclear
Medicine (Ed3). Baltimore, Williams & Wilkins, 1996;50:943-958.

Mettler FA, Guibetreau MJ. Essentials of Nuclear Medicine Imaging, 4th Edition.
W. B. Saunders, Philadelphia. 1998:115-123.

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