TB Flashcards
Describe the pathophysiology of TB.
- Exposure -> innate response involving dendritic cells. TB may die. If not:
- Adaptive response: T cells stimulate macrophages to engulf TB. TB may die, or stay trapped in the macrophage for many years (latent TB)
- Immunocompromise or ageing can lead to reactivation of TB.
What is the Ghon focus?
A granuloma forms a wall around the bacteria, leading to caseous necrosis. This area is called a Ghon focus. In reactivation, memory T cells release cytokines, forming more caseous necrosis.
How is TB spread?
Airborne droplets [pts]
What is a Ghon complex?
The ghon focus (area of necrosis) plus the associated lymph node. Often subpleural and occur in lower lobes.
[osmosis]
Which lobes of the lung does TB spread to and why?
Upper lobes - oxygenation is greatest here, TB is aerobic. [osmosis]
Give 3 complications of TB.
Spreads through lung -> bronchopneumonia Spreads through blood -> miliary TB: -Kidneys - sterile pyuria -Brain - meningitis -Lumbar vertebrae - pott's disease -Adrenal glands - Addison's disease -Liver -hepatitis -cervical LNs - cervical lymphadenitis (scrofula).
What is the mantoux test? How is it performed today compared to previously?
Inject small amount of TB in skin, rapid inflammation means the person has immune memory so has been exposed to TB at some point (including BCG vaccine). It used to be done on skin but now is done in a test tube with the patient’s blood.
How can MDR-TB and XDR-TB be prevented?
Multi-drug resistant and eXtremely drug resistant TB:
- use appropriate antibiotics for the strain of TB
- use multiple medications at the same time
- complete the full course [osmosis]
Give 3 risk factors for TB.
Travel to endemic areas HIV or immunocompromised Close contact with TB Previous treatment - esp incomplete Poverty, homelessness, drug/alcohol abuse. [pts]
Give 3 symptoms of pulmonary TB.
Chronic cough (50%, dry then productive)
Haemoptysis
Pleuritic chest pain (pleural effusion, pleurisy/inflammation)
Dyspnoea
Systemic: Night sweats, fever, weight loss, malaise [ohcm, pts]
Why are people with HIV more susceptible to TB?
They have depleted CD4 T cell count, and these are important cells in the response against TB.
Why are people on treatment for autoimmune diseases more susceptible to TB?
TNF-alpha neutralising drugs reduce TNF-a which is an important part of the response against TB.
Give 3 extra-pulmonary features of TB.
Lymphadenopathy - TB lymphadenitis Abdo pain - GI TB Pott's disease: backache and stiffness - Spinal TB Headache, seizures - CNS TB Sterile pyuria - GU TB Pericarditis - Cardiac TB. [ohcm,pts]
How is TB diagnosed?
- Sputum cultures (L-J agar) and microscopy (ZN)
- CXR
- CT scan
- Mantoux test
- Interferon G release assay
- Test for HIV/Hep B
[pts, handbook]
What stain would you use to look for TB on microscopy? What would the TB look like?
Ziehl-Neelsen stain for alcohol and acid fast bacilli (AAFB). You would see curved rods.
