Lec 8 TB

Question 1

What is morphology of mycobacterium tuberculosis?

Answer 1

aerobic rod-shaped bacterium
acid-fast bacilli
not dyed by gram stain

Question 2

What is pathogenesis of TB infection?

Answer 2

• primarily intracellular
• slow growth rate
• induces granulomatous response in normal host

Question 3

How is TB transmitted?

Answer 3

small aerosol droplets w/ close contact

not transmitted by fomites [articles of clothing, eating utensils]

Question 4

What happens in primary TB infection?

Answer 4

• droplets containing mycobacteria reach alveoli –> develop primary Ghon lesion
• alveolar macrophages are defense
• organism spreads via hilar lymph nodes via lymphatics = Ghon complex or travels via blood stream

in majority of pts, body’s defense mech controls and limits primary infection

Question 5

Which pts are at risk for having clinially apparent primary TB?

Answer 5

• medications [immunotherapy, immune suppressant]
• alcoholism
• HIV
• malignancy

Question 6

What is delayed hypersensitivity in TB?

Answer 6

• develops a few wks after primary infection
• cell mediated immunity

hallmark = development of granulomas + can have caseous necrosis + multinucleated giant cells

high Ca deposition here is why it shows up

Question 7

How is granuloma formed?

Answer 7

alveolar macrophage in contact with TB –> sends out cytokines to recuit T cells

IFN-gamma and TNF-alpha are important in development

IFN-y by T cells; TNF-a by macrophage

Question 8

What is latent TB? how likely does it happen?

Answer 8

small number of TB organisms remain in granuloma in latent state

can develop reactivation

• over lifetime ~10% of normal immune with latent TB develop reactivation; [5% within 2 yrs; 5% after that]
• if HIV = 10% PER YEAR

Question 9

When does skin test conversion develop?

Answer 9

6-8 wks

Question 10

What does TB skin test test? Who gets false pos/neg?

Answer 10

• put small amount of purified protein [PPD] from TB intradermally
• those with acquired cell immunity to TB will get swelling at injection site
• does not distinguish between active TB and previous infection

false positive if past infection with other not tuberculous mycobacteria

false negative if depressed cell immunity

Question 11

What is interferon gamma release assay [IGRA]?

Answer 11

take blood + expose to antigens specific to TB –> cells process it and measure IFN-gamma presented by T cells

helps with false positives but not false negatives

Question 12

What is definition latent tuberculous infection?

Answer 12

+ PPD or +IGRA but no evidence of active disease

Question 13

WHat is defintion TB disease aka active TB?

Answer 13

presence of clinically active disease in 1 or more organ systems ideally with confirmation of diagnosis by isolation of organism

Question 14

What is defintion primary TB?

Answer 14

disease after initial exposure

Question 15

What is definition primary progressive TB?

Answer 15

primary diease that has not been controlled by immune defense mech –> continues to be active beyond point at which delayed hypersensitivity has developed

Question 16

What is reinfection TB?

Answer 16

disease in previously infected person results from exposure to another source of organisms

Question 17

How does TB spread in body?

Answer 17

• during primary infection via blood stream

- can also spread hematogenously to other parts of lung

Question 18

What are characteristic location of reactivation TB?

Answer 18

apical regions of upper lobes b/c less perfused + high PO2 = good for survival

and less so–> superior segment of lower lobes

Question 19

What are clinical feature of TB?

Answer 19

• consumption = weight loss, wasting, loss of appetite
• fatigue, low fever, night sweats
• scarring and loss of lung tissue but resp function generally preserved

pulm symptoms: cough, sputum, hemoptysis

usually insidious rather than acute onset

Question 20

What do you see in chest radiograph from primary TB?

Answer 20

nonspecific infiltrate often in lower lobes

hilar lymphe node enlargement

pleura effusion

when primary disease heals –> small calcified lesions

Question 21

What do you see in reactivation TB on chest radiograph?

Answer 21

apical/posterior segments of upper lobes more affected

infiltrates, cavities, nodules, scarring, contraction

Question 22

What is miliary TB?

Answer 22

progressive widely disseminated hematoenous spread of TB

can arise as result of progressive primary infection or via reactivation

Question 23

How do you diagnose TB?

Answer 23

• stain smears from sputum
• nucleic acid amplification
• culture

Question 24

What is treatment for TB?

Answer 24

need for ~6 months

Question 25

Why do you have to test for latent TB before starting anti-TNF

step1

Answer 25

to make sure you don’t give anti-TNF which inhibits granuloma formation

Question 26

WHat is most common organism of atypical mycobacteria?

Answer 26

mycaobacterium avium complex [MAC]

Question 27

Who gets non-TB mycobacteria?

Answer 27

• pts with underlying lung disease who are immune compromised
• pts with systemic immunity = AIDS

can be localized to lung and mimic TB or hematogenously disseminate in body [particuarly in AIDS]