TB Flashcards
What causes TB
Mycobacterium TB (bacillus)
- M. TB = human only known reservoir
- M. bovis
- MOTT if immunocompromised
What are the RF for TB
Age - elderly Non-UK Known contact with someone with TB HIV - often pushes into active Immunosuppression - knocks latent into active - DM - HIV - Biologics - Anti-TNF - Organ tranplant Chronic renal Malignancy IVDA / alcohol Previous TB Decreased socio-economic ocnditions Malnutrition
What is the source of TB
Open active pulmonary TB cavitating lesion
Transported via resp droplets e.g. cough / sneeze
Two options
- Clear infection = 70% (phagocytksed by macrophages which kill as part of innate)
- Develop primary TB if unable to clear = 30%
What is mycobacterium TB
AAFB so requires ZN stain
Obliqate aerobe - requires O2
Faculative intracellular - prefers in cell e.g. macrophage but doesn’t have to be
What is primary TB and what is it associated with ?
1st infection if macrophages unable to clear
Lungs most commonly affected = 85%
Associated with development of immunity to tuberculoprotein (Mantoux test)
What happens when TB enters hilia of lungs
If infection clears or if primary develops
Macrophage ingest
Release cytokines to attract inflammatory cells
Antigen presenting cells present to CD4 lymphocyte in LN
MHC2 activated and go back to alveoli and kill TB
If this occurs = infection clears and no TB
Primary TB
Epitheliod granuloma forms (collection of macrophage) = Ghon focus
Often caesating - lots of necrosis
Langerhan’s giant cells produced
Can then spread via lymphatics to involve hilar node = Ghon complex
RANKE = focus + complex together
Disease can be contained here latent
What are in Langerhan’s
Macrophages
Found in every granulomatous condition e.g. sarcoid / vasculitis
What and where does primary TB affect
Children
Sub pleural area / UL
What does primary TB present with
Peripheral area of consolidation + hilar lymphadenopathy
Known as Gohn’s complex
What are granulomas
Central area of necrosis due to dead TB
Can calcify
Langerhan’s surround
What are the S+S of primary Tb
Asymptomatic in majority Fever Malaise Erythema nodosum Rarely chest sign
What can happen after primary infection
Primary progressive
Contained latent in lung if T cell response restricts (5-10% of reactivation but not contagious)
Reactivation - usually precipitated by alteration in immune. Can occur in pulmonary and extra-pulmonary site and most common form of active TB in clinic
What can happen after primary infection if don’t clear = primary progressive
If immune unable to suppress infection = TB pneumonia + risk of widespread dissemination (5%)
Usually if inadequate T cell immunity e.g HIV
Progressive consolidation
Bronchiectasis as bronchi collapse due to compression from LN
Pleural effusion
Bronchopneumonia if LN discharge
Hameatagenous spread - miliary and meningeal TB if poor immune
Miliary TB
- Disseminated TB characterised by military changes
Will be fatal if not treated
What are signs of miliary TB
Can be primary TB or reactivation Fine mottling on CXR Small granulomas throughout lung Spread through venous system 100% mortality if not treated Can spread through arterial but would appear septic
What is post primary TB
Reactivation of mycobacterium from latent primary infection
Disseminated by blood
Affects all organs but lungs most common in apex / UL
Who is at risk of post primary TB
Elderly Immunocompromised HIV Organ transplant Lymphoma Drugs - cytotoxic / steroid / biologics IVDU Haemodialysis Malnutrtion DM
What are the symptoms of post primary
Asymptomatic Fever FAtique Weight loss Night sweats Cough Haemoptysis Sputum Pleuritic chest pain SOB Dull ache Finger clubbing Erythema nodosum Lymphadenopathy Crackles Bronchial breathing Signs of effusion and fibrosis Low SATS Systemically unwell
Can get TB in any organ so high degree of suspicion
e.g. if GI = abdominal pain and commit
How do you investigate active TB
CXR = essential for Dx of pulmonary
Bloods - FBC, U+E, LFT
HIV test for all Dx
To Dx active need tissue / fluid
Early morning sputum to try isolate - 3 samples
- Sputum culture = gold standard but 4-6 weeks
- Microscopy for ZN stain will show in 48 hours
- Can do PCR but not routine
- If sputum +ve suggest highly infectious
Other test BAL - ZN stain / PCR Biopsy of LN / liver or areas that don't produce fluid CT thorax - Not everyone needs but useful to see extent of disease Mantoux test Bronchoscopy + biopsy Pleural aspiration
What does CXR show
Fibrosos and cavitatation Patchy shadows / infiltrates Pleural effusion Hilar lympahdneopathy Loss of volume Fibrosis Cavitation / calcification in upper zone if reactivated Miliary TB = millet seeds throughout lungs
How do you check for immunity / latent TB
Mantoux test = intradermal admission of tuberculoprotin results in inflammation after 24 hours
Delayed type 4 reaction
Can also do IGRA which is a blood test
Not affected by previous BCG vaccine or non-TB mycobacteria
