In a population-based study of hyperthyroid patients in India, which is the most common cause of hyperthyroidism in iodine-sufficient urban areas?

Explanation

## Most Common Cause of Hyperthyroidism in Iodine-Sufficient Regions ### Geographic and Epidemiologic Context **Key Point:** In iodine-sufficient regions (including urban India), Graves' disease is the most common cause of hyperthyroidism, accounting for 60–80% of cases. In iodine-deficient regions, toxic multinodular goiter becomes relatively more common. ### Why Graves' Disease Dominates in Iodine-Sufficient Areas 1. **Autoimmune prevalence**: Graves' disease is an autoimmune disorder with genetic and environmental triggers (infections, stress, female sex) 2. **Age distribution**: Peaks in young to middle-aged adults (20–50 years) — the most economically active population 3. **Female predominance**: 5–10 times more common in women 4. **Iodine status**: In adequate iodine intake, the thyroid is larger and more prone to autoimmune attack ### Epidemiologic Comparison by Region | Region | Most Common Cause | Prevalence | Second Most Common | |--------|-------------------|-----------|--------------------| | **Iodine-sufficient (India urban, USA, Europe)** | Graves' disease | 60–80% | Toxic nodular goiter (15–20%) | | **Iodine-deficient (India rural)** | Toxic multinodular goiter | 40–50% | Graves' disease (30–40%) | | **Iodine-replete (post-iodization)** | Graves' disease | 70–80% | Thyroiditis (10–15%) | **High-Yield:** The shift from toxic nodular disease to Graves' disease as the leading cause occurs when iodine supplementation programs are implemented — this is a classic epidemiologic transition. ### Why Other Options Are Less Common **Iodine-induced hyperthyroidism (Jod-Basedow phenomenon)** - Occurs when iodine is introduced to iodine-deficient populations - Rare in iodine-sufficient areas where iodine intake is already adequate - Accounts for <5% of hyperthyroidism in urban India **Toxic nodular goiter** - More common in elderly patients (>50 years) and iodine-deficient regions - Develops over decades from autonomous nodules - In iodine-sufficient regions, accounts for only 15–20% of hyperthyroidism **Thyroid cancer** - Does not cause hyperthyroidism in the acute phase - Thyroid cancer with hyperthyroidism is exceptionally rare and usually occurs with metastatic disease producing ectopic thyroid hormone ### Clinical Implications for India - **Urban India** (iodine-sufficient): Graves' disease is most common → expect young women, autoimmune features - **Rural India** (iodine-deficient): Toxic multinodular goiter more prevalent → expect older patients, nodular disease [cite:Harrison 21e Ch 405]