## Most Common Site of Tuberculosis **Key Point:** Pulmonary tuberculosis (TB) accounts for approximately 80–85% of all TB cases in India and globally. ### Epidemiology of TB Sites | Site | Frequency | Clinical Presentation | |------|-----------|----------------------| | **Pulmonary** | 80–85% | Cough, hemoptysis, fever, night sweats | | Lymph node (extrapulmonary) | 10–15% | Cervical/mediastinal lymphadenopathy | | Meningitis (extrapulmonary) | 1–2% | Meningeal signs, CSF changes | | Abdominal (extrapulmonary) | 1–2% | Ascites, abdominal pain, malabsorption | | Bone/Joint | 1–2% | Spinal/joint involvement | **High-Yield:** Pulmonary TB is the most common form because *Mycobacterium tuberculosis* is primarily transmitted via respiratory droplets and establishes initial infection in the lungs. The patient's presentation (productive cough, sputum smear positivity) confirms pulmonary involvement. ### Why Pulmonary TB is Most Common 1. **Route of transmission:** Airborne droplet nuclei lodge in alveoli 2. **Primary site of infection:** Lungs are the initial and most frequent site 3. **Infectivity:** Smear-positive pulmonary TB is the main source of transmission in the community 4. **Natural history:** Extrapulmonary TB usually follows hematogenous dissemination from a primary pulmonary focus or reactivation **Clinical Pearl:** While extrapulmonary TB occurs in 15–20% of TB cases (higher in immunocompromised patients), pulmonary TB remains the most common presentation even in HIV-coinfected individuals in India.
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