Ultrasound images demonstrate diffusely heterogeneous echotexture of the the thyroid gland, without discrete nodules. The right lobe is mildly enlarged. Compare the above images with this example of normal thyroid echotexture:

The patients lab results from her initial encounter came back as:
TSH <0.02 uiU/ml (Normal 0.50-4.50)
Free T4 3.6 ng/dL (Normal 0.8-1.8)

She underwent further evaluation with Iodine 123 imaging:

The Iodine 123 scan shows markedly decreased activity in the thyroid gland. The 24-hour uptake was measured as 2% (normal 10-30%).

The differential diagnosis for decreased radioiodine uptake in a thyrotoxic patient includes:

• Subacute thyroiditis
• Iodine-induced thyrotoxicosis
• Amniodarone-induced thyrotoxicosis (type 2)
• Thyrotoxicosis factitia (exogenous thyroid hormone)
• Struma ovarii

Ziessman HA, O’Malley JP, Thrall JH, eds. Nuclear Medicine, the Requisites, 4th ed. Philadelphia: Elsevier, 2014.

Given this patient’s ultrasound findings and lack of another cause for thyrotoxicosis, this case is a classic example of subacute thyroiditis.

Subacute thyroiditis has both painful (Granulomatous/de Quervain’s thyroiditis) and painless (silent thyroiditis and postpartum thyroiditis) forms, and can be due to a preceding viral illness. The initial presentation is classically with thyrotoxicosis, followed by a brief hypothyroid phase, before return of euthyroid state in 6-12 months.

Here are our patient’s labs (normal TSH 0.50-4.50, normal free T4 0.8-1.8):

• presentation: TSH <0.02 uiU/ml, Free T4 3.6 ng/dL
• 1 month: TSH 15.1 uIU/ml, Free T4 0.5 ng/dL
• 2 months: TSH 6.3 uIU/ml, Free T4 0.7 ng/dL
• 4 months: TSH 3.5 uIU/ml, Free T4 0.8 ng/dL
• 12 months: TSH 4.0 uIU/ml, Free T4 1.0 ng/dL

Here is schematic diagram of the 3 phases of subacute thyroiditis as illustrated in this case.

Based on Figure 6-14. Ziessman HA, O’Malley JP, Thrall JH, eds. Nuclear Medicine, the Requisites, 4th ed. Philadelphia: Elsevier, 2014.