Tuberculosis (TB) Flashcards
What is TB?
A chronic granulomatous infectious disease caused by the bacteria : Mycobacterium tuberculosis.
Epidemiology (& Risk Factors) of TB (3).
More prevalent in :-
1. Non-UK Born Patients (South Asia).
2. Immunocompromised e.g. HIV.
3. Close Contacts with TB.
What is Multi-Drug Resistant TB?
Strain resistant to more than one TB drug, making it difficult to treat - use amikacin, macrlides, quinolones and capreomycin.
Nature of Mycobacterium tuberculosis (3).
- Small Rod-Shaped Bacillus.
- Waxy Coating (makes Gram-Staining Ineffective).
- Acid-Fast (Resistant to the acids used in the staining procedure).
Staining of Mycobacterium tuberculosis.
Ziehl Neelsen Stain : Bright Red against Blue Background.
What property of Mycobacterium tuberculosis makes it difficult to culture?
Very slow dividing with high Oxygen demands.
Transmission of TB.
Inhalation of saliva droplets from infected people, spreading through lymphatics and blood.
What is a Granuloma?
An aggregate of activated epithelioid macrophages - walling off viable organisms in anoxic and acidic environment.
Pathophysiology of Pulmonary TB (5).
- Lung Lesion - Ghon Focus develops (tubercle-laden macrophages).
- Ghon Complex = Ghon Focus + Hilar Lymph Nodes.
- Granuloma Formation with Caseous Necrosis in Centre.
- Inflammatory Response : Type 4 Hypersensitivity Reaction.
- Th2 Driven (usually Th1 Driven in good health to form granulomas).
- Immunocompetent = Healing by Fibrosis. Immunocompromised = Disseminated Disease.
What is Active TB?
Active infection in various areas within the body.
What is Latent TB?
When the immune system encapsulates sites of infection to stop the progression of the disease.
What is Secondary TB?
Reactivation of Latent TB.
What is Military TB?
When the immune system is unable to control the disease, this causes a disseminated severe disease.
Sites of TB Infection (2H).
- Pulmonary : Lungs (Oxygen Supply).
- Extrapulmonary :
2A. Lymph Nodes (Cervical - Scrofuloderma).
2B. Pleura.
2C. CNS (Tuberculous Meningitis).
2D. Pericardium.
2E. GI System.
2F. GU System (commonest).
2G. Bones and Joints.
2H. Cutaneous TB (Skin).
What does TB in the Lymph Nodes cause?
A ‘cold abscess’ - firm painless abscess in the neck with no inflammation, redness and pain (unlike an acutely infected abscess).
What is Spinal TB known as?
Pott’s Disease of the Spine.
Clinical Presentation of TB (2).
- Chronic Gradually Worsening Symptoms.
- 70% Pulmonary TB (but with Systemic Symptoms).
Clinical Features of TB (5).
- Constitutional Symptoms.
- Cough +/- Haemoptysis.
- Lymphadenopathy.
- Erythema Nodosum.
- Spinal Pain (Spinal TB).
Investigations of TB (2B).
- Ziehl-Neelsen Stain.
- Immune Response to TB Tests :
2A. Mantoux Test.
2B. IGRA Test.
Indication of Mantoux Test (3).
- Previous Vaccination to TB.
- Latent TB.
- Active TB.
Method of Mantoux Test (2).
- Inject tuberculin into the intradermal forearm to create a bleb under the skin.
- After 72 hours, measure the induration of the skin at the site of injection.
What is Tuberculin?
A collection of tuberculosis proteins that have been isolated from the bacteria - the infection does not contain any live bacteria.
Mantoux Test Results (3).
- Negative : Induration < 6mm (no significant hypersensitivity to tuberculin protein - can give BCG if unvaccinated).
- Positive : Induration of 6-15 mm (hypersensitive - previous TB infection or BCG - don’t give BCG).
- Strongly Positive : Induration > 15mm (hypersensitive - TB infection).
Give 5 false negative causes of the Mantoux test.
- Military TB.
- Sarcoidosis.
- HIV.
- Lymphoma.
- Very Young (< 6 Months).
Method of IGRA Test (2).
- Mix TB antigens with a sample of blood.
- WBCs that are already sensitised will release Interferon-Gamma as part of the immune response.
Indication of IGRA Test.
Positive Mantoux test but no features of Active TB in order to confirm a diagnosis of Latent TB.
What would a CXR show in TB (3)?
- Primary : Patchy Consolidation, Pleural Effusions and Bilateral Hilar Lymphadenopathy.
- Reactivated : Patchy/Nodular Consolidation with Cavitation (Gas Spaces in Lungs) in Upper Zones.
- Military : ‘Millet Seeds’ uniformly distributed throughout the lung fields.
Cultures in TB (3).
- Sputum - 3 Samples Collected and Tested (Hypertonic Saline to induce Sputum / Bronchoscopy with Lavage to collect Sputum Samples).
- Mycobacterium Blood Cultures.
- Lymph Node Aspiration or Biopsy.
When would a NAAT be useful?
Only if the information would affect treatment or the patient is at a higher risk of developing complications e.g. HIV.
What can decrease the sensitivity of a sputum smear?
HIV.
Management of Latent TB (2B).
- No Treatment - Healthy.
- Risk of Reactivation :
2A. Isoniazid and Rifampicin - 3 Months.
2B. Isoniazid - 6 Months.
Why are there 2 options in Latent TB management?
A : People Younger than 35 if Hepatotoxicity is a concern.
B : Interactions with Rifamycins are a concern e.g. HIV, Transplant.
Management of Acute TB (2D).
- MDT.
- RIPE Combination :
2A. Rifampicin - 6 Months.
2B. Isoniazid - 6 Months.
2C. Pyrazinamide - 2 Months.
2D. Ethambutol - 2 Months.
What is given with Isoniazid Prophylactically?
Pyridoxine (Vitamin B6) - Isoniazid causes peripheral neuropathy.
Important Management Considerations of TB (4).
- Test for Infectious Diseases e.g. HIV.
- Contact Testing.
- Public Health England.
- Isolation until Established on Treatment (2 Weeks).
How are patients with Active TB isolated in hospital?
Negative pressure rooms have ventilation systems that actively remove air to prevent it spreading out on to the ward to prevent airborne spread.
Management of Meningeal Tuberculosis.
Prolonged period - at least 12 months - with addition of steroids.
What is Direct Observed Therapy (DOT) (3)?
3x a weekly dosing regimen indicated in certain groups e.g. :-
1. Homeless People.
2. Poor Concordance.
3. Prisoners.
Medication Information for Patient.
Take RIPE all together on empty stomach 1 hour before breakfast.
What is the BCG Vaccine?
An intradermal infection of live attenuated TB.
What is the BCG Vaccine useful for and not useful for?
Useful : Severe and Complicated TB.
Not Useful For : Pulmonary TB (Less Effective).
Conditions for the BCG Vaccine (2).
- Mantoux Test Negative.
- Immunosuppression and HIV Negative (Live Vaccine).
Relationship between HIV and TB (3).
- Depletion of M. tuberculosis-specific CD4 T Lymphocytes and Type I Cytokine Production.
- Dysfunction of the CD4 T Lymphocyte-Macrophage Immune Axis.
- Impairs Host’s Ability to Form Granulomas.
