W5 - TB Flashcards
Name 7 groups vulnerable to TB in the UK
Those from high prevalence countries
HIV positive, immunosuppressed
Elderly, neonates
Diabetics, kidney disease
Homeless, alcoholics, IDUs
Mental health problems
Prisons
In 2021, 68% of global cases of TB were in how many countries?
8
What % of UK TB cases are in London? Why?
39%
Immigration from high incidence areas
How is TB incidence changing each year? TB is what # killer of communicable diseases? How many people are infected worldwide?
2% fall per year
2nd largest killer, after Covid
2 billion people infected worldwide
What infective agent causes TB?
Mycobacterium tuburculosis
What 3 diseases can mycobacterium cause?
TB
Atypical mycobacteria
Leprosy
Mycobacteria has what 3 characteristics?
Non-motile bacillus = very slow growing
Aerobic = likes apices of lungs
Very thick fatty cell wall
A very thick fatty cell wall makes mycobacteria resistant to what 6 things?
Acid
Alkali
Detergent
Neutrophil destruction
Macrophage destruction
Ziehl Neilson Stain (AAFB)
In what 2 ways can mycobacteria be eliminated?
UV radiation
Dilution
How is TB spread and what is the exception?
Airborne (pulmonary & laryngeal TB)
Exception: M. bovis which is spread through consumption of unpasturised infected cow milk
Outline the immunopathology of TB - when we breathe in mycobacterium, what happens?
- Breathe in mycobacterium
- Mycobacterium ends up in alveoli
- Macrophages react in a TH1 Immune Mediated Response
- TH1 cells in LNs activate macrophages
- They turn to epitheloid cells which accumulate into Langerhans giant cells
- They form granulomas (to encapsulate infection)
This can lead to central caseating necrosis and potential calcification
Explain why the Th1 cell mediated immunological response is a double-edged sword
It eliminates/reduces the number of invading mycobacterium
But
Tissue destruction is a consequence of activation of macrophages
What 2 factors influence the outcome of infection?
Virulence and number of pathogens
What 4 factors determine a patient’s suceptibility to an infection?
Genetics
Nutrition
Age
Immunosuppression
Explain how mycobacterium spreads in a primary infection
Via lymphatics to draining hilar LNs
Outline the 5 symptoms of primary infection of TB
Asymtomatic (most common)
Fever
Malaise
Erythema nodosum
Rarely chest signs
Primary infection can result in immunity to what?
Tuberculoprotein
What are the 3 potential outcomes of TB primary infection?
Progressive disease
Contained latent
Cleared cured
What is TB bronchopneumonia and its 3 features? What’s the prognosis?
Progression of primary infection.
Enlargement of primary focus (cavitation)
Enlarged hilar LN compress bronchi, lobar collapse
Enlarged LN discharges from bronchus
Poor prognosis
What does Miliary TB affect and what does it look like on CXR?
Affects multiple organs
CXR
Fine mottling
Widespread small granulomata
What are the 2 main hypotheses around post-primary TB?
- TB bacteria enter dormant stage with no/low replication
- Balanced state of replication and destruction by immune mechanisms
Miliary, meningeal and pleural TB take how long to develop symptoms?
6-12 months
Post primary disease, pulmonary and skeletal TB take how long to develop symptoms
Typically 1-5 years. Maybe 30-40
Genitourinary and cutaneous TB take how long to develop symptoms?
Typically 10-15 years. Maybe 30-40
What are the 5 symptoms of TB?
Cough
Fever
Sweats (mainly at night)
Weight loss
Some/all above symptoms missing
What does post-primary TB look like on CXR?
Apices with soft fluffy or nodular upper zone
Cavitation in 10-30%
Following CXR, what 5 things may make you consider CT?
Normal CXR but clinical suspicion
Miliary TB
Cavitation and other differential
Lymphadenopathy, alternative diagnosis
Targets for BAL
What 4 things does primary TB look like on CXR?
Mediastinal lymphadenopathy
Pleural effusion
Miliary
Pneumonic lesion with enlarged hilar nodes
Aside from scans, what 5 tests can we do for TB?
Sputum (3 samples; 8-24h gap, 1+ early morning)
Induced sputum
Broncoscopy with BAL
EBUS with biopsy
Aspirate/biopsy from tissue
What test can we do for CNS TB?
Lumbar puncture
What test can we do for urogenital TB?
Urine test
What 3 tests are useless for active TB?
Mantoux
IGRA
Blood tests
How do we treat TB?
Multidrug therapy, either 4:2 or 2:4 for 6+ months
Describe the public health duties of doctors managing cases of Tuberculosis
We have a legal requirement to notify all cases
Name 5 drugs for treating TB
Rifampicin
Isoniazid
Pyrazinamide
Ethambutol
Steroids
What are the 5 side effects of rifampicin?
Irn Bru urine/tears/lenses
Induces liver enzymes (so use prednisolone and anticonvulsants)
Hormonal contraceptive ineffective
Hepatitis
Rash
What are the 3 side effects of isoniazid?
Hepatitis
Peripheral neuropathy (manage with pyridoxine - vit B6)
Rash
What are the 3 side effects of pyrazinamide
Hepatitis
Gout
Rash
What are the 2 side effects of ethambutol?
Optic neuropathy
Rash
To what 3 at-risk groups is the BCG vaccination given to?
Unvaccinated kids under 5 with parents/grandparents from high-incidence countries
Contacts of cases
High risk employees
Describe the effectiveness of the BCG vaccination
Reduces risk of severe forms of TB, mainly in kids but doesn’t stop you from getting it
What 3 groups are screened for latent TB?
Contacts of people with active TB over 65 years
New entrants to area with high incidence
Pre-biologics (TNF-alpha inhibitors)
What 2 tests are used to screen for latent TB?
Mantoux skin test
Interferon Gamma Release Assay (IGRA) blood test
A latent TB (LTBI) diagnosis is made if what 4 conditions are met?
Asymptomatic
Normal CXR
Normal exam
Positive Mantoux/IGRA
In what 3 potential ways is latent TB treated
Rifampicin+isoniazid for 3 months
Isoniazid or rifampicin for 6 months
Rifapentine+isoniazid once weekly for 12 weeks
