A 34-year-old woman presents to the outpatient clinic with a 3-month history of palpitations, heat intolerance, and weight loss despite good appetite. On examination, she has a resting heart rate of 110/min, fine tremor of the hands, and a diffuse, non-tender thyroid enlargement. Her TSH is <0.01 mIU/L (normal 0.4–4.0), free T4 is 28 ng/dL (normal 7–18), and free T3 is 8.5 pg/mL (normal 2.3–4.2). Thyroid peroxidase (TPO) antibodies and thyroglobulin antibodies are negative. Thyroid uptake scan shows diffusely increased uptake. 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-stimulating antibodies (TRAb). ### Clinical Presentation in This Case 1. **Diffuse thyroid enlargement** — uniform, non-nodular goiter is characteristic of Graves' disease 2. **Elevated free T3 and T4** — indicates true thyroid hormone overproduction 3. **Suppressed TSH** — reflects negative feedback from excess thyroid hormone 4. **Diffusely increased thyroid uptake on scan** — confirms autonomous thyroid hormone synthesis (not destruction or exogenous source) 5. **Negative TPO/thyroglobulin antibodies** — rules out Hashimoto's thyroiditis; note that TRAb (not measured here) would be positive in Graves' disease ### Why Diffuse Uptake Matters | Feature | Graves' Disease | Toxic Multinodular Goiter | Thyroiditis | |---------|-----------------|---------------------------|-------------| | **Thyroid uptake** | Diffusely increased | Patchy/nodular uptake | Low/absent | | **Thyroid size** | Diffuse enlargement | Nodular enlargement | Normal or enlarged | | **Duration** | Gradual onset | Insidious, years | Acute/subacute | | **Antibodies** | TRAb positive | Negative | Negative | **Clinical Pearl:** In Graves' disease, the TSH receptor antibodies stimulate the entire thyroid gland uniformly, producing diffuse uptake on radioiodine scan. This distinguishes it from toxic nodules (focal uptake) and thyroiditis (suppressed uptake). ### High-Yield Mnemonic: GRAVES **G** — Goiter (diffuse) **R** — Receptor antibodies (TRAb+) **A** — Autoimmune **V** — Vascular (bruit, increased blood flow) **E** — Eye signs (exophthalmos, lid lag) **S** — Suppressed TSH ### Management Approach ```mermaid flowchart TD A[Graves' Disease Diagnosed]:::outcome --> B{Treatment Choice}:::decision B -->|First-line in India| C[Antithyroid drugs: PTU/MMI]:::action B -->|Refractory/intolerant| D[Radioactive iodine or surgery]:::action C --> E[Beta-blocker for symptom relief]:::action E --> F[Remission or progression to ablation]:::outcome ``` [cite:Harrison 21e Ch 405]