Lecture 8: TB

Question 1

What shape is TB? What stain? Intra/extracellular?

Answer 1

Aerobic, rod-shaped; acid-fast; intracellular

Question 2

Describe primary TB infection

Answer 2

Mycobacteria in alvoeli –> Gohn lesion (small focus) –> spread (hilar lymph nodes) to distant organs or lung apex

Question 3

Generally, what happens after primary infection?

Answer 3

Body’s defense control it and leaves only scarring

Question 4

In 5% of patients, you can get (during the primary infection)…

Answer 4

Progressive primary TB (due to immunosupression, alcoholism…)

Question 5

What causes the development of granulomas?

Answer 5

Cell-mediated hypersensitivity

Question 6

Describe the process of healing granulomas

Answer 6

Fibrosis often with deposition of calcium

Question 7

What surrounds caseous center of a granuloma?

Answer 7

Macrophages that have become epithelioid histiocytes, surrounded by lymphocytes and fibroblasts

Question 8

Which cell begins the process of granuloma formation? What happens?

Answer 8

Alveolar macrophages: come in contact with TB, secrete cytokines, interact w/ lymphocytes

Question 9

Describe latent TB

Answer 9

TB not totally cleared creating balance b/t TB and immune system, but majority of patients will never have further difficulty

Question 10

Describe reactivation TB (%)

Answer 10

Immune system weakens; 10% will reactivate (50% within 2 years, 50% for rest of life)

Question 11

What is injected in PPD? Does it distinguish b/t active TB or previous infection? Why might you get a false negative? False positive?

Answer 11

Small amount of purified TB protein; nope; impaired cell-mediated immunity; if you’ve had infection w/ other mycobacterium

Question 12

What’s an alternative to PPD? Why is this test better?

Answer 12

Interferon-gamma release assay; antigens used are specific to TB

Question 13

Does IGRA solve the immuno compromised problem?

Answer 13

Nope! Still must develop cellular immunity

Question 14

During primary spread, organism spreads through the…

Answer 14

Bloodstream (to other organs and lung)

Question 15

Characteristic location of reactivation TB

Answer 15

Higher lobes of lungs: high pO2 and less perfusion (likes aerobic bacilli, dislikes immune cells in the blood)

Question 16

Why is TB called consumption?

Answer 16

Patient looks consumed: weight loss, wasting, loss of appetite

Question 17

How does TB affect lung function and V/Q matching?

Answer 17

Respiratory function preserved because the disease is in upper lungs; no V/Q mismatch because ventilation and perfusion destroyed simultaneously

Question 18

TB systemic symptoms (4)

Answer 18

Weight loss, fatigue, night sweats, low-grade fever

Question 19

TB pulmonary symptoms (3)

Answer 19

Cough, sputum, hemoptysis

Question 20

Chest radiograph (primary, healed primary, reactive, miliary)

Answer 20

Primary: non-specific infiltrate in lower lobes (+/-) lymph enlargement, effusion; Healed primary: small calcified lesions; Reactivation: apical lobes with infiltrates, cavities, nodules, scarring, contraction; Miliary: dots all over lungs

Question 21

Describe miliary TB

Answer 21

Progressive, disseminated hematogenous spread of TB (primary or secondary) that looks like millet seeds

Question 22

Diagnose TB methods

Answer 22

1. Stained smears looking for acid fast bacilli via sputum sample; 2. Nucleic acid amplification (requires fewer organisms, more specific); 3. Culture (required for drug susceptibility)

Question 23

TB Treatment

Answer 23

Active: multiple agents for 6 months – isoniazid, rifampin, pyranzinamide, ethambutol

Question 24

Who do you treat if they have latent TB?

Answer 24

People who are exposed to those with active infection or the immunocompromised

Question 25

Describe non-TB mycobacteria: most common organism, those at risk

Answer 25

There are many and they are potential pulmonary pathogens, most common is MAC (mycobacterium avium complex); ppl with lung disease or immunocompromised

Question 26

BCG vaccine: living? greatest benefit? who do you give it to?

Answer 26

Live strain of another mycobacterium; diminishes risk of TB meningitis and disseminated disease in children; neonates in countries with high prevalence