A 34-year-old woman from Delhi presents with a 3-month history of palpitations, heat intolerance, and weight loss despite good appetite. On examination, she has a diffuse thyroid enlargement, fine tremor, and a resting heart rate of 110 bpm. Her TSH is <0.01 mIU/L (normal 0.4–4.0), free T4 is 28 pg/dL (normal 7.5–20), and free T3 is 8.5 pg/mL (normal 2.3–4.2). Thyroid peroxidase (TPO) antibodies and thyroglobulin antibodies are negative. Technetium-99m pertechnetate uptake is markedly elevated. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Graves' Disease ### Key Diagnostic Features **Key Point:** Graves' disease is the most common cause of hyperthyroidism (60–80% of cases) and is an autoimmune condition mediated by TSH receptor antibodies (TRAb). ### Why Graves' Disease Fits This Case 1. **Diffuse thyroid enlargement** — uniform, smooth goiter (not nodular) 2. **Elevated radioiodine uptake** — Tc-99m pertechnetate shows diffuse, high uptake across the entire gland 3. **Negative antibody testing** — TPO and thyroglobulin antibodies are negative, but TSH receptor antibodies (TRAb) would be positive (not routinely tested in this vignette, but clinical picture is pathognomonic) 4. **Young woman** — Graves' disease has a female predominance (5–10:1) and typically presents in the 3rd–4th decade 5. **Classic systemic features** — palpitations, heat intolerance, weight loss, fine tremor, tachycardia ### Differential Diagnosis Table | Feature | Graves' Disease | Toxic Multinodular Goiter | Thyroiditis | TSH-oma | | --- | --- | --- | --- | --- | | **Goiter appearance** | Diffuse, smooth | Nodular | Tender or firm | Diffuse | | **Radioiodine uptake** | Diffuse, high | Patchy/nodular | Low/absent | Low | | **TSH** | Suppressed | Suppressed | Suppressed | Elevated | | **Age of onset** | Young (20–40) | Older (>50) | Variable | Rare | | **Antibodies** | TRAb positive | Negative | TPO/Tg may be positive | Negative | | **Thyroid pain** | No | No | Yes | No | **High-Yield:** The combination of **diffuse goiter + high radioiodine uptake + suppressed TSH + young woman** is pathognomonic for Graves' disease. ### Pathophysiology Graves' disease is driven by IgG autoantibodies against the TSH receptor (TRAb), which: - Bind to and activate TSH receptors on thyroid cells - Stimulate thyroid hormone synthesis and release - Cause thyroid growth (goiter) - Are NOT blocked by negative feedback (unlike TSH) **Clinical Pearl:** Graves' disease is the only form of hyperthyroidism that causes **both** thyroid enlargement AND exophthalmos (due to orbital fibroblast activation by TRAb). This patient may develop eye signs if not treated promptly. ### Management Implications First-line treatment in India typically includes: - Antithyroid drugs (PTU or methimazole) - Beta-blockers for symptom control - Consideration of radioiodine ablation or thyroidectomy for definitive management [cite:Harrison 21e Ch 405]