What is the most common cause of primary adrenal insufficiency (Addison disease) worldwide?

Explanation

## Epidemiology of Addison Disease **Key Point:** Autoimmune adrenalitis is the most common cause of primary adrenal insufficiency (Addison disease) worldwide, accounting for approximately 70–90% of cases in developed nations and increasingly recognized as the global leader as TB control has improved. ### Global Epidemiologic Context According to Harrison's Principles of Internal Medicine (21e, Ch. 375) and standard endocrinology references, **autoimmune adrenalitis** is the leading cause of primary adrenal insufficiency globally. It accounts for: - **70–90%** of cases in developed (Western) countries - An increasing proportion of cases worldwide as tuberculosis prevalence has declined with improved public health measures Tuberculosis was historically a major cause and remains important in high-burden regions, but it is no longer the global leader in absolute case numbers. ### Comparative Causes of Primary Adrenal Insufficiency | Cause | Prevalence (Global) | Key Features | |-------|-------------------|-------------| | **Autoimmune adrenalitis** | ~70–90% (most common worldwide) | Adrenal atrophy, 21-hydroxylase autoantibodies, associated with other autoimmune conditions (APS-1, APS-2) | | **Tuberculosis** | ~7–20% (historically higher) | Bilateral adrenal enlargement, calcification on CT, concurrent TB findings | | **Adrenal metastases** | 5–10% | Known malignancy (lung, breast, lymphoma), bilateral involvement | | **Adrenoleukodystrophy** | 1–2% | X-linked, elevated VLCFA, progressive neurologic symptoms | **Clinical Pearl:** Autoimmune adrenalitis is characterized by: - Bilateral adrenal **atrophy** on imaging (vs. enlargement in TB) - Presence of **21-hydroxylase antibodies** (most specific marker) - Association with other autoimmune endocrinopathies (Type 1 DM, Hashimoto thyroiditis, vitiligo) — Autoimmune Polyglandular Syndrome (APS) - Gradual onset over months to years ### Why Autoimmune Adrenalitis is the Global Leader 1. **Immune-mediated destruction:** CD4+ and CD8+ T-lymphocytes target adrenocortical cells, particularly those expressing 21-hydroxylase (CYP21A2). 2. **Declining TB burden:** Global TB control programs have significantly reduced TB-related adrenal disease. 3. **Diagnostic recognition:** Improved serologic testing (21-OH antibodies) has increased detection of autoimmune cases worldwide. 4. **APS associations:** APS-2 (Schmidt syndrome) — Addison disease + autoimmune thyroid disease ± Type 1 DM — is the most common polyglandular syndrome. **High-Yield:** For NEET PG/INI-CET, the standard answer for "most common cause of Addison disease worldwide" is **autoimmune adrenalitis**. Tuberculosis is the answer only when the question specifically asks about "developing countries," "high TB-burden regions," or "historically." **Mnemonic — Causes of Addison's (CATAMITE):** - **C**alcification (TB) - **A**utoimmune ← Most common worldwide - **T**uberculosis ← Most common in developing/high-burden regions - **A**drenoleukodystrophy - **M**etastases - **I**nfections (fungal, CMV in AIDS) - **T**rauma/hemorrhage - **E**ndothelial dysfunction (sepsis, DIC — Waterhouse-Friderichsen) [cite: Harrison 21e Ch. 375; Williams Textbook of Endocrinology 14e]