Tuberculosis Flashcards
Describe the epidemiology of TB
30% of the world’s population have latent TB
2 billion deaths from TB each year
Highest incidence in central and southern africa
Describe the aetiology of TB
Caused by mycobacterium tuberculosis
Gram stain -ve but similar structure to gram stain +ve.
Unique impermeable cell wall
Transmission predominantly from aerosolised droplets or fomites.
Where is latent TB often contained in the body?
Hilar lymph nodes and Ghon focus
Describe the histopathology of TB
Granulomatous inflammation with caseous necrosis
List the host risk factors for TB
Extremes of age
Stress and starvation
Immunocompromised host:
- HIV
- Alcoholism
- Steroids and immunosuppressants
- Anti TNF treatment for autoimmune diseases
Other risk factors:
- Malignancy
- Renal failure
- Diabetes mellitus
- Vitamin D deficiency
Name some clinical features of TB
Varies according to site of infection; insidious onset.
Systemic features:
- Fevers
- Night sweats
- Weight loss
Pulmonary:
- Cough
- Sputum
- Haemoptysis
- Dyspnoea
Lymph nodes = typically cervical & axillary (may become necrotic)
Other sites = local symptoms of inflammation & tissue necrosis
List investigations for TB
- Full blood count (FBC) : possible leukocytosis (↑ WCC)
- Urea & electrolytes (U&Es) : usually normal
- Liver function tests (LFTs) : possibly raised
- C-reactive protein (CRP) : mild-moderate rise only
- Lactate : usually normal (no sepsis)
- Chest radiograph (CXR) : upper lobe cavitating pneumonia
- Miliary shadowing
- Hilar lymphadenopathy
- Pleural effusion
- Pericardial effusion
CT/MR scans : thorax / abdomen / spine / bones / head
Laparoscopy / Thoracoscopy : direct visualisation & biopsy
Other biopsies : lymph nodes / bones / cold abscesses
What does this x-ray show?
Left upper lobe tuberculosis
What does this x-ray show?
Miliary TB (TB infection was never contained in ghon focus, spread throughout body tissues)
What does this x-ray show?
Pericardial effusion caused by TB.
Large due to slow growing TB
Which microbiological investigations can be conducted to confirm TB?
Sputum:
- Ziehl-Neelsen stain → Acid-Fast Bacilli (AFBs) = pink
- Auramine-Phenol stain → AFBs = fluorescent
Sputum, pleural fluid, pericardial fluid, blood, urine, CSF & biopsies→ culture (on Löwenstein–Jensen or liquid medium) & sensitivities
How is TB treated?
Multi-drug treatment required to prevent resistance
- Rifampicin for 6 months
- Isoniazid for 6 months
- Pyrazinamide for 2 months
- Ethambutol for 2 months
(TB in the CNS requires 12 months of treatment)
Pyridoxine to prevent neuropathy from isoniazid
Steroids if CNS or pericardial infection
Vitamin D if deficient
What can be given to prevent TB?
Prevention of primary infection :
For active TB cases :
- Respiratory isolation
- Prompt diagnosis & treatment
- Contact tracing & testing
Vaccination with Bacillus Calmette–Guérin (BCG) :
- ~25% prevention of primary infection
- ~70% prevention of active infection
How is latent TB screened for?
What is the treatment of latent TB?
Prevention of re-activation :
- Screening for latent TB infection & treatment :
- Tuberculin skins tests (TST)
- TB interferon-gamma release assays (IGRA)
Treatment for latent TB :
- Rifampicin & isoniazid for 3 months