Anterior images from an iodine 123 thyroid scan with and without markers at the thyroid cartilage and suprasternal notch demonstrate uniformly markedly decreased thyroid activity (circle). This low uptake is confirmed on the uptake portion (normal, 10–30% at 24 hours).

Differential Diagnosis

•  Subacute thyroiditis: In a thyrotoxic patient, markedly decreased thyroid radioiodine accumulation on thyroid uptake and scan is most commonly due to this entity.

•  Thyrotoxicosis factitia: This entity, as well as amiodarone-or iodine-induced thyrotoxicosis and struma ovarii, can appear identical to thyroiditis on thyroid uptake and scan but are less common and usually do not include neck tenderness.

•  Graves disease: