Tuberculosis Flashcards
What organism causes tuberculosis
Mycobacterium tuberculosis complex bacteria
What organism most commonly causes TB?
Mycobacterium tuberculosis
Describe the pathogenesis of TB
- aerosols inhaled
- engulfed by alveolar macrophages
- at this point most have a spontaneous recovery
- those who don’t > primary TB (latent or disseminated)
- if latent, TB can reactive causing post primary TB
Describe the mycobacterium tuberculosis
- non motile bacilli
- obligate aerobe
- long chain fatty acids + glycolipids in cell wall
- slow growing
- acid fast bacilli
Risk factors of TB
- Close contact with patient infected with pulmonary TB
- high prevalence in India + sub-Sahara Africa
- extremes of age
- homelessness
- diabetes
- immunosuprresion e.g. HIV
- alcohol or drug dependence
- prolonged steroid use
Risk factors for reactivation of TB
- infection with HIV
- substance abuse
- prolonged therapy with corticosteroids
- organ transplant
- diabetes mellitus
- low body weight
- severe kidney disease
Why can gram stain not be used for mycobacterium tuberculosis?
What is used instead?
Gram satin cant go through thick fatty acid cell wall
ZN staining
What are the three types of TB disease?
Pulmonary TB
Extrapulomary TB
Miliary TB
Site of miliary TB
Carried to all parts of the body through bloodstream
Who is extrapulmonary TB often found in?
HIV infected
Immunosuppressed
Young children
Symptoms of pulmonary TB
- fever
- night sweats
- weight loss/anorexia
- fatigue
- cough
- haemoptysis
- malaise
- breathlessness if pleural effusion
Signs of pulmonary TB on examination
- often no chest signs despite CXR abnormalities
- crackles in affected area
Extrapulmonary presentation of TB
- erythema nodosum
- meningitis
- lymphadenopathy
- pericardial effusion
- cold abscess
What is a cold abscess in TB?
a firm painless abscess, often in the neck
Investigation of pulmonary TB
- CXR
- consider CT chest if CXR not typical
- histology
- if productive cough, 3x ZN stain + TB culture
- Mantoux test
- Interferon-gamma release assay
- NAAT
How does a TB infection appear on CXR?
- often at apex
- ill defined patchy consolidation
- cavitation within consolidation
- healing results in fibrosis
What is a ghon focus?
How does it form?
- spherical granuloma with central caseation, caused by the macrophages ingesting Mycobacterium tuberculosis
- three weeks after infection, immune cells surround site of infection > granuloma
- this isolates bacteria to prevent spreading
- tissue inside granuloma dies > caseous necrosis
- the necrotic area is a ghon focus
What is a ghon complex?
- to infection spread to hilar lymph nodes
- the caseating tissue (ghon focus) + associated lymph node is the ghon complex
What can be done if a suspected TB patient isn’t producing enough sputum for culture?
- sputum induction with nebulised hypertonic saline
- bronchoscopy + bronchoalveolar lavage
Diagnosis of TB
sputum/blood cultures (gold standard) but can take months so nucleic acid amplification tests done as it is faster
Outline nucleic acid amplification tests
- assess for genetic material of pathogen
- performed on sputum sample
- provides info about bacteria faster than a culture
What is NAAT used for?
diagnosing TB in patients with HIV or under 16
Diagnosing latent TB
Mantoux test (tuberculin skin test)
Interferon Gamma Release Assay
Outline the Mantoux Test
- injecting tuberculin into the intradermal space on the forearm
- infection creates a bleb under the skin
- the bleb is measured after 72 hours
- > 5mm is positive
Outline interferon-gamma release assays
- mixing a blood sample with M.tuberculosis antigens
- if there is a previous infection, WBCs will release interferon-gamma
- positive result if interferon-gamma is released
Where is TB common?
Africa
Asia
Latin America
How does post primary TB arise?
Reactivation of latent infection
What does primary TB lead to?
- asymptomatic latent TB (more common)
- primary progressive pulmonary/extrapulmonary TB through dissemination
Main sites of extrapulmonary TB
- CNS
- pleura
- bones + joints
- urogenital tract
What is miliary TB?
Form of TB characterised by widespread dissemination to extrapulmonary organ causing tiny lesions
What is suggestive of miliary TB on chest x ray?
Many tiny spots throughout lung field
What do all patients with miliary TB need + why?
CT/MRI head +/- LP
to exclude CNS involvement e.g. TB meningitis/CNS TB
Lumbar puncture results of TB meningitis/CNS TB
high protein
low glucose
lymphocytosis
What vaccination is given to prevent TB?
Describe it
What must be done before the vaccine?
- BCG vaccine
- intradermal injection of live attenuated mycobacterium bovis > creates immune response + immunity to M.tuberculosis
- tested with Mantoux test, risk of immunosuppression + HIV
Who is the TB vaccine given to?
- those at increased risk of TB
- healthcare workers
Treatment of latent tuberculosis
isoniazid + rifampicin for 3 months
OR
isoniazid for 6 months
First line medication for active TB
How long must each be taken for?
Rifampicin: 6 months
Isoniazid: 6 months
Pyrazinamide: 2 months
Ethambutol: 2 months
.
take all for 2 months and then continue for 4 months with just rifampicin + isoniazid
Management of TB
- notify public health England
- admit to negative pressure side room + start infection control measures
- routine bloods (especially LFTs)
- HIV test
- screening + tracing of close contacts
- medications: isoniazid, rifampicin, pyrazinamide + ethambutol
Due to certain side effects of TB drugs, what must be done before and during treatment?
- risk of hepatitis + visual disturbances
- baseline LFTs + visual acuity tests
- monitor both whilst on treatment
Side effects of TB drugs
- hepatitis: rifampicin, isoniazid, pyrazinamide
- visual disturbance: ethambutol
- peripheral neuropathy: isoniazid
- orange secretions: rifampicin
Side effects of rifampicin
Orange urine/secretions
Hepatitis
Thrombocytopaenic rash
side effects of isoniazid
- hepatitis
- rashes
- peripheral neuropathy
- psychosis
Side effects of pyrazinamide
- hepatitis
- rashes
- vomiting
- arthralgia
Side effects of ethambutol
visual disturbances
What must always be given with isoniazid?
Why?
pyridoxine (vit B6)
Avoid damage to peripheral nerves
What skin findings can arise with TB?
Erythema nodosum
Pulmonary complication for TB
- pleurisy
- plural effusion
- empyema
- pneumothorax
- bronchiectasis
- respiratory failure
