Lecture 8: TB Flashcards
What shape is TB? What stain? Intra/extracellular?
Aerobic, rod-shaped; acid-fast; intracellular
Describe primary TB infection
Mycobacteria in alvoeli –> Gohn lesion (small focus) –> spread (hilar lymph nodes) to distant organs or lung apex
Generally, what happens after primary infection?
Body’s defense control it and leaves only scarring
In 5% of patients, you can get (during the primary infection)…
Progressive primary TB (due to immunosupression, alcoholism…)
What causes the development of granulomas?
Cell-mediated hypersensitivity
Describe the process of healing granulomas
Fibrosis often with deposition of calcium
What surrounds caseous center of a granuloma?
Macrophages that have become epithelioid histiocytes, surrounded by lymphocytes and fibroblasts
Which cell begins the process of granuloma formation? What happens?
Alveolar macrophages: come in contact with TB, secrete cytokines, interact w/ lymphocytes
Describe latent TB
TB not totally cleared creating balance b/t TB and immune system, but majority of patients will never have further difficulty
Describe reactivation TB (%)
Immune system weakens; 10% will reactivate (50% within 2 years, 50% for rest of life)
What is injected in PPD? Does it distinguish b/t active TB or previous infection? Why might you get a false negative? False positive?
Small amount of purified TB protein; nope; impaired cell-mediated immunity; if you’ve had infection w/ other mycobacterium
What’s an alternative to PPD? Why is this test better?
Interferon-gamma release assay; antigens used are specific to TB
Does IGRA solve the immuno compromised problem?
Nope! Still must develop cellular immunity
During primary spread, organism spreads through the…
Bloodstream (to other organs and lung)
Characteristic location of reactivation TB
Higher lobes of lungs: high pO2 and less perfusion (likes aerobic bacilli, dislikes immune cells in the blood)
Why is TB called consumption?
Patient looks consumed: weight loss, wasting, loss of appetite
How does TB affect lung function and V/Q matching?
Respiratory function preserved because the disease is in upper lungs; no V/Q mismatch because ventilation and perfusion destroyed simultaneously
TB systemic symptoms (4)
Weight loss, fatigue, night sweats, low-grade fever
TB pulmonary symptoms (3)
Cough, sputum, hemoptysis
Chest radiograph (primary, healed primary, reactive, miliary)
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
Describe miliary TB
Progressive, disseminated hematogenous spread of TB (primary or secondary) that looks like millet seeds
Diagnose TB methods
- 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)
TB Treatment
Active: multiple agents for 6 months – isoniazid, rifampin, pyranzinamide, ethambutol
Who do you treat if they have latent TB?
People who are exposed to those with active infection or the immunocompromised
Describe non-TB mycobacteria: most common organism, those at risk
There are many and they are potential pulmonary pathogens, most common is MAC (mycobacterium avium complex); ppl with lung disease or immunocompromised
BCG vaccine: living? greatest benefit? who do you give it to?
Live strain of another mycobacterium; diminishes risk of TB meningitis and disseminated disease in children; neonates in countries with high prevalence
