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DR DEAC PIMPs
>
Tuberculosis
Definition
Infection by M. tuberculosis or M. bovis
Risk Factors
Low BMI
HIV
Alcohol
Travel
Immunosuppressed
Genetic component?
Crowded living conditions
Vegetarianism
Elderly / young
Lung damage (silicosis etc)
Diabetes
Renal failure
Smoking (20+ => 2-3x risk)
Differential diagnosis
Pneumonia
Noicardiosis
Upper zone fibrosis:
Sarcoidosis
Lung cancer
Extrinsic allergic alveolitis
Single unilateral infiltrate
Sarcoidosis
Carcinoma
Bilateral infiltrates
Sarcoidosis
Hilar lymphadenopathy
Sarcoidosis
Lymphadenopathy (other cause)
Multiple cavities
Pneumonia (cf timing)
Wegener's granulomatosis
PMF (progrssive massive fibrosis)
Single cavities
Abscess
Carcinoma
Rheumatoid
Legionella
Anthrax
Mesothelioma (aspestos cancer)
Epidemiology
1/3 of world infected
African/asian/indian/eastern europe
2-3 million die per year
1 new infection per second
>40/100,000 = 'Endemic'
15 - 23% of AIDS deaths are from TB
On the rise
99% of infections don't show (many) symptoms and => latent
10% of latent infections will reactivate later
Aetiology
Droplets in air spread mycobacteria
Usually infects lungs initially
Immune response to bacteria causes damage
Clinical features
Upper zone fibrosis
Bacteria prefer high up (more oxygen)
Night sweats
Productive cough
Fever and
Weight loss
Anorexia
Pleural effusion
Finger clubbing
Rales
Pneumonia
Pathophysiology
Type IV hypersensitivity
Bacteria enveloped by macrophages
Waxy cell wall => resistant to breakdown
MCHII presentation, T cell activation
Primary focus (Gohn focus)
Secondary foci in lymph nodes
=> Il1, IL12, TNFa release
=> PMN infiltration
Macrophages turn into
Epitheliod cells
Which fuse to form Langhans cells
Fibroblasts infiltrate and lay down fibrin
=> caseating granulomas
Investigations
Hx
Mantoux
Positive result is:
>5mm HIV
>10mm high-riskers
>15mm everyone else
NB false positives
Steroids
Immunosuppression
Milliary TB?
Quantiferon-TB Gold
=> IFN-g levels
CXR
Nodules
Cavities
Little scars
Hilar caseous lymph nodes
Upper lobe
Sputum
3 different samples
ZN stains
Bacteria in sputum (direct visualisation) => infective
Bacteria can be cultured => latent?
Takes 3 weeks
Management
NB DOTS treatment
Directly observed treatment, short duration
Isoniazid
6 months
Blocks mycolic acid synthesis
Peripheral neuropathy
Prevent with vitamin B6 injections
Rifampicin
6 months
Inhibits DNA polymerase
Stains body fluids pink
Ethambutol
2 months
Blocks
arabinosyl transferase
=> blocks cell wall production
Colour vision -
Pyrazinamide
First 2 months only
Blocks fatty acid synthesis?
Or disrupts membrane potential?
Joint pain
Pyridoxine
2 months
Reduces ioniazid side-effects
Prognosis
Untreated active disease kills 50%
Miliary TB almost 100% fatal
Treatment very effective if followed
Secondary TB
Peyers patches
Mesentary
Spine (Pott's spine)
Liver
Miliary TB (blood-born foci)
Scrofula of neck (lymphatic spread)
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