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Pulmonary tuberculosis (PTB) is a chronic granulomatous infection of the lung caused primarily by Mycobacterium tuberculosis, transmitted via aerosolized droplets. It remains a major global health burden, especially in developing countries, and manifests as primary or post-primary (reactivation) TB, each with distinct clinical and radiological patterns.
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Etiopathogenesis
Causative Organism
- Mycobacterium tuberculosis complex (MTBC), primarily M. tuberculosis.
Transmission
- Airborne: inhalation of droplets from infected individuals.
Pathogenesis
- Primary TB:
- Occurs in naïve (previously unexposed) individuals, often children.
- Bacilli implant in mid-lung zone → Ghon focus.
- Drainage to hilar lymph nodes forms Ghon complex.
- Heals with fibrosis and calcification → Ranke complex.
- May disseminate (miliary TB) or progress locally.
- Post-primary (reactivation) TB:
- Reactivation of latent bacilli, usually in immunocompromised or malnourished adults.
- Localized to posterior segments of upper lobes or superior segments of lower lobes.
- Causes cavitation, fibrosis, and bronchogenic spread.
- Miliary TB:
- Hematogenous spread leading to diffuse micronodular disease.
Clinical Features
| Primary TB |
Post-primary (Reactivation) TB |
| Common in children |
Common in adults |
| Often asymptomatic |
Insidious onset: cough, fever, night sweats, weight loss |
| Hilar lymphadenopathy prominent |
Cavitary lesions, hemoptysis |
| May progress to miliary TB |
Fibrosis, volume loss, bronchiectasis |
Complications
- Hemoptysis
- Bronchopleural fistula
- Chronic cavitary disease
- Aspergilloma