The pathogenicity of Mycobacterium tuberculosis is caused by which of the following mechanisms?
A Is impaired antibody response/cell mediated
B Is a hypersensitivity response to products of the tuberculosis bacteria
C Is due to caseous necrosis
D Is direct host cell killing by the bacillus
B Is a hypersensitivity response to products of the tuberculosis bacteria
Causative agent of TB
Mycobacterium tuberculosis
Acid-fast bacillus (AFB)
Obligate aerobe
High lipid content in cell wall (mycolic acid)
what type of hypersensitivity is TB
type IV hypersensitivity
what is a Ghon focus and a Ghon complex
Ghon focus (subpleural granuloma, often in lower/middle lung zones)
Ghon complex = Ghon focus + involved hilar lymph nodes
what is secondary TB
Reactivation of latent TB due to immunosuppression
Affects apices of lungs (higher oxygen tension)
More tissue necrosis and cavitation
May spread locally or via bloodstream (→ miliary TB)
what is histopathology of TB
Type IV hypersensitivity (T-cell mediated)
Caseating granulomas (central necrosis)
Central: eosinophilic, acellular debris (caseous necrosis)
Surrounding: epithelioid histiocytes, Langhans giant cells, lymphocytes
AFB positive with Ziehl–Neelsen stain
what tests are used to diagnose TB
AFB stain
Culture (Lowenstein-Jensen medium)
NAAT / PCR
Mantoux test / Quantiferon Gold
Which of the following statements is correct regarding pulmonary tuberculosis?
A The Ghon focus is a parenchymal peri-hilar lesion
B Bacilli establish themselves in sites of low oxygen tension
C Liquefactive necrosis precedes the formation of granulomata
D Langhans cells occur in coalescent granulomata
D Langhans cells occur in coalescent granulomata
The Ghon focus is a subpleural parenchymal lesion (often in mid-lung zones), not perihilar.
Mycobacterium tuberculosis prefers areas of high oxygen tension (apices of lungs), as it is an obligate aerobe.
Liquefactive necrosis occurs later in progressive disease (cavitary lesions).
The most frequent site of a primary tuberculous lesion in lung is?
A Apex
B Hilum
C Lower zone of upper lobe
D Peripherally
C Lower zone of upper lobe
Primary tuberculosis (TB) implants in the lower part of the upper lobe or the upper part of the lower lobe. Secondary TB occurs near the apical pleura
