A 35-year-old woman presents with palpitations, heat intolerance, and weight loss despite good appetite. On examination, she has a diffuse thyroid enlargement, lid lag, and exophthalmos. What is the most common cause of hyperthyroidism in this patient?

Explanation

## Most Common Cause of Hyperthyroidism **Key Point:** Graves' disease is the most common cause of hyperthyroidism worldwide, accounting for 60–80% of all cases of thyroid hormone excess. ### Clinical Features Pointing to Graves' Disease The clinical presentation in this case is pathognomonic: - **Diffuse thyroid enlargement** (smooth, uniform goiter) - **Exophthalmos** (eye protrusion — unique to Graves') - **Lid lag** (delayed descent of upper eyelid on downward gaze) - **Systemic symptoms:** palpitations, heat intolerance, weight loss These features together form the classic triad of **Graves' disease: hyperthyroidism + goiter + eye signs (Graves' ophthalmopathy)**. ### Pathophysiology Graves' disease is an **autoimmune disorder** caused by IgG antibodies against the **TSH receptor (TSHR)**, which: 1. Bind to TSH receptors on thyroid follicular cells 2. Stimulate thyroid hormone synthesis and release (mimicking TSH action) 3. Cause thyroid hypertrophy and hyperplasia → diffuse goiter 4. Cross-react with orbital fibroblasts and preadipocytes → orbital inflammation, adipogenesis, and exophthalmos **High-Yield:** The presence of **exophthalmos and lid lag** is virtually diagnostic of Graves' disease and distinguishes it from other causes of hyperthyroidism. ### Epidemiology | Feature | Graves' Disease | Toxic Multinodular Goiter | Thyroiditis | | --- | --- | --- | --- | | **Frequency** | 60–80% of hyperthyroidism | 10–15% | 5–10% | | **Age of onset** | 20–40 years (female > male, 5:1) | >50 years | Variable | | **Goiter** | Diffuse, smooth | Nodular, irregular | Often absent or tender | | **Eye signs** | Yes (exophthalmos, lid lag) | No | No | | **Antibodies** | Anti-TSHR, anti-TPO, anti-thyroglobulin | None | Anti-TPO (variable) | | **Course** | Chronic, relapsing-remitting | Progressive | Self-limited (weeks to months) | **Clinical Pearl:** Graves' disease is the only cause of hyperthyroidism that produces **orbital manifestations** (exophthalmos, myositis, optic neuropathy). This clinical finding alone makes it the diagnosis. ### Why Other Causes Are Less Common - **Toxic multinodular goiter:** Second most common (10–15%), but typically occurs in older patients (>50 years) with long-standing nodular disease; no eye signs. - **Thyroiditis:** Accounts for only 5–10% of hyperthyroidism; is self-limited and presents with thyroid pain/tenderness; no goiter enlargement in most cases. - **TSH-secreting pituitary adenoma:** Rare cause of hyperthyroidism; would show elevated TSH (not suppressed), which is the opposite of the expected lab pattern. [cite:Harrison 21e Ch 405]