A 42-year-old woman presents with palpitations and weight loss. Serum TSH is suppressed and free T4 is elevated. A Tc-99m pertechnetate thyroid scan shows intense, well-defined uptake confined to a nodule in the left upper lobe, with markedly reduced uptake in the remainder of both lobes. The most likely diagnosis is:

• A Graves disease
• B Toxic autonomous adenoma (Plummer disease) ✓
• C Subacute (de Quervain) thyroiditis
• D Follicular thyroid carcinoma

Explanation

An autonomously functioning nodule secretes hormone independently of TSH, suppressing pituitary TSH and thereby reducing pertechnetate uptake by the normal extranodular tissue. This produces a single intensely hot nodule on a cold background. In Graves disease the entire gland shows diffuse uniform increased uptake. Subacute thyroiditis gives globally low uptake, and a malignant nodule is almost always cold, never hyperfunctioning.

Reference: Mettler, Essentials of Nuclear Medicine Imaging, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.