Which of the following is the most common cause of hyperthyroidism worldwide?

Explanation

## Epidemiology of Hyperthyroidism **Key Point:** Graves' disease accounts for 60–80% of all hyperthyroidism cases globally, making it the single most common cause. ### Causes of Hyperthyroidism — Frequency Ranking | Cause | Prevalence | Mechanism | | --- | --- | --- | | **Graves' disease** | 60–80% | TSH receptor antibodies (IgG); autoimmune | | Toxic multinodular goiter | 10–15% | Autonomous thyroid nodules | | Toxic adenoma | 5–10% | Single autonomous nodule | | Thyroiditis (subacute, postpartum) | 5–10% | Inflammation → hormone release | | Iodine-induced (Jod-Basedow) | <5% | Excess iodine in iodine-deficient areas | | Pituitary adenoma (TSH-secreting) | <1% | Rare; secondary hyperthyroidism | **High-Yield:** In iodine-replete regions (including India), Graves' disease dominates. Iodine deficiency causes hypothyroidism and goiter, not hyperthyroidism. ### Graves' Disease — Pathophysiology 1. Autoimmune production of TSH receptor antibodies (TRAb) 2. Antibodies bind TSH receptor → mimic TSH signaling 3. Continuous stimulation of thyroid → thyroid hormone overproduction 4. Diffuse thyroid enlargement (diffuse goiter) 5. Extrathyroidal manifestations: ophthalmopathy, dermopathy **Clinical Pearl:** Graves' disease is the only cause of hyperthyroidism that presents with **exophthalmos** and **pretibial myxedema** — these features are pathognomonic and help distinguish it from other causes. **Mnemonic:** GRAVES = **G**oiter, **R**adioacitve uptake (high), **A**ntibodies (TRAb), **V**alues (T3/T4 high, TSH low), **E**xophthalmos, **S**ystemic (autoimmune).