Tuberculosis
(TB)
Epidemiology:
- Risk populations:
- Immigrants
- Urban poor
- Elderly
- AIDS
- Diseases that
increase the risk:
- DM
- Hodgkin’s
lymphoma
- Chronic lung
disease (esp silicosis)
- Chronic renal
failure
- Malnutrition
- Alcoholism
- immunosuppression
Common sites:
Gross features:
- primary infection:
- Ghon complex:
- 1 to
1.5cm gray-white pleural-based consolidation (Ghon
focus) which undergoes caseous necrosis
- caseation
of hilar lymph nodes
- Resolution:
- Progressive fibrosis
of Ghon complex
- Calcification of
Ghon complex (Ranke
complex)
- progressive
primary infection (at risk individuals):
- lower and middle
lobe consolidation without cavitation
- hilar lymphadenopathy
- reactivation TB:
- initial lesion
<2cm consolidation within 1-2cm of the apical pleura
- sharply
circumscribed, firm, gray-white to yellow
- central caseation and peripheral fibrosis
- apical disease
with cavitation
- progressive
reactivation TB (at risk individuals):
- erosion of caseation into a bronchus leaving a cavity
- miliary pulmonary TB:
- 2mm foci of
yellow-white consolidation scattered through the lungs
- pleural
effusions
- tuberculous empyema
- obliterative fibrous pleuritis
- systemic miliary TB:
- most prominent
in liver, bone marrow, spleen, adrenals, meninges,
kidneys, fallopian tubes, and epididymis
- any organ
- intestinal TB:
- ulcerations,
particularly in the ileum
Histologic features:
- granulomatous inflammatory reaction
- caseating and non-caseating
tubercles
- enclosed within
a fibroblastic rim punctuated by lymphocytes
- multinucleate
giant cells within the granulomas
- Note: immunosuppressed patients may not form a granulomatous response
- Instead, sheets
of foamy histiocytes packed with mycobacteria on acid-fast stains
- Tubercle bacilli
can be demonstrated in early exudative and caseous phases of granuloma
formation
- Not found in
late, fibrocalcific stages
Immunophenotype:
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Marker:
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Sensitivity:
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Specificity:
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Molecular features:
Other features:
- Mycobacterium tuberculosis
- Reservoir is
humans
- Macrophages are
the primary cells infected
- Active inhibition
of fusion of phagosome with lysosome
- TH1 ---à IFN-gamma ---à TNF response
- Infection is
usually asymptomatic, leaving only a fibrocalcific
nodule at the site of infection
- When immune
defenses are lowered, infection may reactivate
- Tuberculin (Mantoux) test:
- Palpable induration peaks in 48-72h (delayed hypersensitivity reaction)
References: