A 32-year-old woman from Delhi presents with a 3-month history of palpitations, tremor, and heat intolerance. She reports weight loss of 4 kg despite good appetite. On examination, she is anxious, has a resting heart rate of 110 bpm, fine tremor of outstretched hands, and a diffuse, non-tender thyroid enlargement. Her TSH is <0.01 mIU/L (normal 0.4–4.0), free T4 is 28 pg/dL (normal 7.5–21), and free T3 is 8.2 pg/dL (normal 2.3–4.2). Thyroid peroxidase (TPO) antibodies are negative. Technetium-99m thyroid uptake is uniformly increased. Which is the most likely diagnosis?

Explanation

## Diagnosis: Graves' Disease ### Clinical Presentation **Key Point:** The constellation of diffuse thyroid enlargement (goiter), elevated free T3 and T4, suppressed TSH, and uniformly increased radioiodine uptake is pathognomonic for Graves' disease. ### Diagnostic Criteria Met | Feature | Finding | Significance | |---------|---------|---------------| | **Thyroid enlargement** | Diffuse, non-tender | Characteristic of Graves'; nodular pattern would suggest toxic MNG | | **Free T4 & T3** | Both elevated | Confirms primary hyperthyroidism | | **TSH** | Suppressed (<0.01) | Indicates autonomous thyroid function | | **Radioiodine uptake** | Uniformly increased | Diffuse uptake excludes thyroiditis (low uptake) and MNG (patchy uptake) | | **TPO antibodies** | Negative | Graves' is not primarily autoimmune against TPO; TSI (TSH receptor antibodies) would be positive | ### Pathophysiology **High-Yield:** Graves' disease is caused by IgG antibodies against the TSH receptor (TSI—thyroid-stimulating immunoglobulin), which activate the receptor and mimic TSH signaling, leading to: 1. Unregulated thyroid hormone synthesis and release 2. Thyroid growth (diffuse goiter) 3. Orbital and dermal manifestations (Graves' ophthalmopathy, pretibial myxedema) in ~30% of cases ### Why Uniformly Increased Uptake Excludes Other Diagnoses **Clinical Pearl:** The **uniform** distribution of radioiodine uptake is the key discriminator: - **Toxic multinodular goiter (MNG):** Patchy/heterogeneous uptake in autonomous nodules; suppressed uptake in non-nodular tissue - **Thyroiditis (subacute, silent, postpartum):** Low or absent uptake because inflammation causes release of preformed hormone, not new synthesis - **Iodine-induced hyperthyroidism:** History of iodine exposure (contrast, amiodarone); low uptake initially ### Age & Demographics **Key Point:** Graves' disease has a peak incidence in women aged 20–50 years, making this 32-year-old woman a typical presentation. [cite:Harrison 21e Ch 397]