TB Flashcards
(12 cards)
TB
- Definition
- Causative agent
Tuberculosis- bacterial infection
Caused by Mycobacterium TB
- Acid-fast bacillus
- Thick cell wall, does not Gram stain well
Classifications
- Primary TB: new TB infection, mainly asymptomatic and can progress
- Latent TB
- Secondary TB
Pulmonary presentation of TB
Productive cough
- Rust coloured
sputum/ Blood if there are cavities
Fever/ malaise/ weight loss
Dyspnoea
Presentation of TB
Can be asymptomatic
Pulmonary: cough, haemoptysis, dyspnoea
CNS (if it disseminates)
- Meningitis = headache, drowsy, meningism, papilloedema, CN palsy
Lymphatic
- Scrofula= cervical lymphadenititis
- Painless neck mass
GU
- Dysuria, haematuria
- Sterile pyuria
Active TB diagnosis
Blood test
- FBC= raised
Tuberlin skin test
- Not very specific
Interferon gamma release assay
- Much more specific
- Reveals if one has been exposed to TB
Imaging
- CXR: consolidation, cavitation, fibrosis, calcification in upper lobes
Sputum sample
- 3 samples= acid fast, culture, nucleic acid application test.
- Culture, microscopy (Ziehl Neelsen stain)
PCR
CXR findings for active TB
Consolidation
Calcification
- Indicates Ghon focus= sub pleural lesion formed from calcified granuloma, in upper lower lobe
Ghon complex
- Calcification from Ghon focus with infection of adjacent lymph nodes/ hilarity nodes
Fibrosis
TB pathophysiology
TB infects alveoli cells and are endocytose by macrophages.
TB released protein that prevents fusion of lysosome with phagosome.
- TB’s thick capsule also prevents degradation by ROS.
- Allows TB to keep growing in macrophage and eventually kill it.
Macrophage releases which causes the formation of granuloma that centres necrotic material
- Call caseous granuloma
- Granuloma contains granulation tissue which includes; macrophage, lymphocytes
Interferon gamma release assays
Determines if someone has been exposed to TB.
- Will not be positive for BCG
Process
- Pt lymphocytes are incubated with TB antigens
- If there has been previous exposure= IFN-G release from T cells
Tuberculin skin test
- Definition
- Process
- Causes of false negatives/ positives
Non-specific test to show if someone has been exposed to TB.
- Type 4 sensitivity
Process
1. Interdermal injection purified protein from TB—> left for 48-72 hours
2. Will show false positive for BCG= >15 mm
No BCG= >6mm
Causes of false positives
- BCG
- Other mycobacteria infections
False negative
- HIV
- Sarcoid
- Lymphoma
Primary investigations for TB
CXR
- Fibronodular opacities in upper lobes
- Can show cavitation
- Atypically= opacities in lower lobes, hilar/ paratracheal lymphadenopathy, pleural effusion
Sputum acid-fast bacilli smear
- Will be positive
- Non-specific as also positive for non-TB mycobacterium
Sputum culture
- The most sensitive and specific test
- Growth takes weeks.
FBC
- Raised WCC
- May show anaemia
Nucleic acid amplification tests
- On sputum/ sterile body fluid
- Positive for MTB
- Very quick results= <8 hours
Latent TB
- Definition
- Treatment
Occurs when MTB in inactive in granuloma
Treatment
- Isoniazid + pyridoxine
- Rifampicin = daily, for 4 months
Active TB treatment
- Initial phase= 5 drugs, 2 months
- Isoniazid + pyridoxine
- Rifampicin
- Pyrazinamide + ethambutol - Continuation phase= 3 drugs, 4 months
- Isoniazid + pyridoxine
- Rifampicin
Treatment is successful when sputum smear is negative.
Treatment of MDR TB
Prolonged treatment= 18-24 months
- At least 6 drugs MTB is likely to be sensitive to
- Intensive phase = 4 months
- Gatifloxacin/ Moxifloxacin + 6 other drugs, including the continuation phase drugs for active TB. - Continuation phase= 5 months
- 4 drugs
