Thyroiditis vs Graves — RACP Adult Medicine MCQ

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ModerateEndocrinology & DiabetesThyroiditis vs GravesRACP Adult Medicine

A 40-year-old woman presents with thyrotoxicosis (suppressed TSH, elevated free T4 and T3). She has a painless, firm, diffusely enlarged thyroid. Radioactive iodine uptake scan shows ABSENT uptake. What is the most likely diagnosis?

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Correct answer: C — Subacute thyroiditis

Absent radioiodine uptake in the setting of thyrotoxicosis indicates that the thyroid is NOT actively synthesising hormones. This occurs in thyroiditis (subacute/de Quervain's – painful; silent/postpartum – painless), exogenous thyroid hormone ingestion, and struma ovarii. A painless, firm thyroid with absent uptake is most consistent with painless (silent) thyroiditis, which is autoimmune in nature and self-limiting. Treatment is supportive (beta-blockers for symptoms). In contrast, Graves' disease shows INCREASED diffuse uptake, and toxic MNG shows patchy uptake.

Reference: eTG – 2025 – Endocrinology