Paper I
Question
Clinicopathological classification of tuberculosis.
Answer
Primary tuberculosis
- Occurs in a previously unexposed (non-sensitized) individual, typically in childhood
- Forms the “Ghon complex” — a peripheral, usually subpleural lung lesion (Ghon focus) with caseous necrosis, together with caseous hilar/mediastinal lymph node involvement
- Usually heals with fibrosis and calcification; may occasionally progress to progressive primary tuberculosis (in immunocompromised/malnourished individuals) or disseminate (miliary tuberculosis)
Secondary (post-primary/reactivation) tuberculosis
- Occurs in a previously sensitized host, either by reactivation of a dormant primary lesion or by re-infection
- Classically localized to the apex of one or both upper lobes (site of highest oxygen tension)
- Characterized by a more vigorous, well-organized immune (Th1) response, producing well-formed caseating granulomas with cavitation
- More likely to progress to symptomatic, communicable disease with cavitary lung destruction
Clinicopathological forms/complications
- Localized pulmonary tuberculosis: Fibrocaseous cavitary disease, typically apical
- Miliary tuberculosis: Haematogenous dissemination producing numerous small (millet seed-sized) granulomas across multiple organs (lung, liver, spleen, kidney, bone marrow, meninges)
- Extrapulmonary tuberculosis: Lymphadenitis (scrofula), skeletal tuberculosis (Pott’s disease of the spine), tuberculous meningitis, renal/genitourinary tuberculosis, gastrointestinal tuberculosis, tuberculous pericarditis/peritonitis
- Isolated organ tuberculosis: May occur from haematogenous seeding without clinically evident miliary disease