Flashcards in Tuberculosis And Asthma Deck (63)
What are the 3 most common bacteria associated with human TB??
Describe some features of mycobacterium tuberculosis
Has a very thick layer of fatty acids, glycolipids etc
Need Acid-Fast stain (cannot stain with Gram stain)
Why does mycobacterium TB take a long time to culture?
Relatively slow growing bacteria
Generation time 15-20 hours
Takes a minimum of 2 weeks to culture
How is TB spread?
Respiratory droplets (coughing/sneezing)
Infectious dose is very low
Air remains infectious for 30 minutes
Is it easy to catch TB?
Usually need prolonged exposure to catch it
What are the classic situations in which TB spreads?
Describe the pathogenesis of TB
Engulfed by alveolar macrophages
Drainage of lung to local lymph nodes
Primary complex/focus of infection established
Progression to primary active disease or initial containment of infection to latent
What are the 2 outcomes of latent infection?
Reactivation of post-primary TB
What is the commonest type of TB?
Reactivation of latent to post-primary TB
Describe how tests for latent TB would appear
TST (mantoux) and IFN gamma tests would be positive
Chest x-ray normal
Sputum smears and cultures normal
What are the main symptoms of active TB
What is miliary TB?
TB disseminated wide into the body via the blood stream
(Tiny spots throughout lung fields on x-ray)
What are some of the risk factors for reactivation?
Prolonged corticosteroid therapy
TNF alpha antagonist
Low body weight
Severe kidney disease
What are caseating granulomata in TB?
Lung parenchyma and lymph nodes
Liquified and cheesy looking material
Dead and dying bacilli and inflammatory cells
Langhan's giant cells present
What are the common sites for extrapulmonary TB?
Bones and joints
What are some risk factors for TB
Non-Uk born/recent migrants
Close contacts of patients with TB
What Hx would suggest TB?
Contacts with TB
List some symptoms of pulmonary TB
What are some signs on examination of pulmonary TB?
Often no chest signs
May be crackles in infected areas
(Pleural involvement = dullness)
What investigations would you run for TB??
Sputum - 3 early morning samples
Induced sputum via physiotherapy
What would you see on a CXR for TB?
Apex of the lung often involved
Ill defined patchy consolidation
Cavities can develop in consolidation
Healing results in fibrosis
Why are sputum smears not very good in diagnosing TB?
Not very sensitive
May only have a few bacilli in
What is the gold standard investigation for diagnosis of TB?
Culture (but takes approximately 2 weeks)
What are epitheloid cells?
(Can fuse together to form giant cells)
Describe the tuberculin sensitivity test (TST)/mantoux
Look for latent TB
Challenge with an antigen previously exposed to
Inflammation, red circle appear at injection site
Read 2-3 days later
(Can get false positives and false negatives)
Describe interferon gamma releasing assays (IGRAs)
Buffer test for latent TB
No cross reaction with BCG
Cannot distinguish between latent and active TB
What is the first line medication for TB?
4 first line medications:
What are some problems with Rifampicin?
Can give orange secretions (tears/urine)
Cannot take whilst on the contraceptive pill
What is the bad side effect of ethambutol?
Can cause visual disturbance