Flashcards in Pathology of TB Deck (10):
What causes TB?
inhalation of aerosolized Mycobacterium tuberculosis
What arises with initial (exogenous) exposure to TB?
*after 3 weeks a Th1 response is mounted, producing interleukin, which drives the macrophages to become competent to contain the organism.
*Note only 5-10% of these people develop clinically significant disease.
What does PRIMARY TB result in?
focal, caseating necrosis in the lower lobe of the lung and hilar lymph nodes that undergoes fibrosis and calcification, forming a Ghon complex (classically sub-pleural).
Is PRIMARY TB usually symptomatic?
NO, but after 6-8 weeks it will produce a positive PPD test.
What is SECONDARY (endogenous) TB?
- reactivation of Mycobacterium tuberculosis from a Ghon complex, due to AIDS, aging, or TNF-a inhibiting drugs.
- it occurs at the apex of the lung due to the high O2 tension and poor lymphatic drainage here.
- this forms cavitary foci of caseous necrosis and may lead to miliary pulmonary TB or tuberculous bronchopneumonia.
What are the clinical features of SECONDARY TB?
- fevers, night sweats, cough with hemoptysis and weight loss (cachexia).
How do you diagnose SECONDARY TB?
biopsy reveals caseating granulomas and AFB stain reveals acid-fast bacilli (this property allows the bacteria to retain the stain even after treatment with a mixture of acid and alcohol).
What are the high-yield sites of systemic spread of TB?
- meninges (meningitis at the BASE of the brain)
- cervical lymph nodes
- kidneys (sterile pyuria)- MOST COMMON extrapulmonary site.
- adrenals (Addison's disease)
- lumbar vertebrae (Pott's disease)
How does Mycobacterium tuberculosis prevent phagosome-lysosomal fusion inside the macrophages?
via a protein (CORD FACTOR) that inhibits Ca2+ signals