Which is the most common site of involvement in tuberculosis-induced Addison disease?

Explanation

## Tuberculosis-Induced Addison Disease: Pathology and Site of Involvement ### Pathological Features of TB-Adrenalitis **Key Point:** Tuberculosis causes bilateral adrenal destruction in >90% of TB-induced Addison cases. The hallmark histological finding is caseating granulomas (tubercles) with central caseous necrosis, epithelioid cells, and Langhans giant cells. ### Why Bilateral Involvement Occurs 1. **Haematogenous spread:** TB disseminates via bloodstream during primary infection or reactivation, seeding both adrenal glands simultaneously. 2. **Rich vascular supply:** The adrenal glands have extensive blood flow, making them a common site for miliary TB. 3. **Threshold for insufficiency:** Approximately 90% of adrenal cortical destruction is required before clinical Addison disease manifests; bilateral involvement ensures this threshold is exceeded. ### Histological Pattern | Feature | TB-Adrenalitis | Autoimmune Adrenalitis | |---------|----------------|------------------------| | Bilateral involvement | >90% | ~95% | | Histology | Caseating granulomas | Lymphocytic infiltration, fibrosis | | Adrenal calcification | Common ("eggshell" pattern) | Absent | | Speed of onset | Acute to subacute | Gradual (months to years) | | Associated TB elsewhere | Pulmonary, renal, bone | None | ### Clinical Implications **High-Yield:** In endemic TB regions, always suspect TB-induced Addison disease if: - Bilateral adrenal enlargement or calcification on imaging (CT/ultrasound) - History of TB or TB exposure - Acute presentation of adrenal insufficiency - Elevated inflammatory markers (ESR, CRP) **Clinical Pearl:** "Eggshell" calcification of the adrenal glands (rim-like calcification) is pathognomonic for TB-adrenalitis and helps differentiate it from autoimmune disease (no calcification) or metastatic disease (irregular calcification). ### Why Unilateral Disease Does Not Cause Addison Unilateral adrenal destruction (even if complete) is insufficient to cause clinical adrenal insufficiency because the contralateral gland can maintain adequate cortisol and aldosterone production. Addison disease requires bilateral involvement. **Mnemonic: "90-90 Rule" for TB-Adrenalitis** **90%** of the adrenal cortex must be destroyed for insufficiency **90%** of TB-adrenalitis cases are bilateral [cite:Robbins 10e Ch 24]