Tuberculosis Flashcards
What is the epidemiology of TB?
Globally decreasing.
Higher in deprived areas of the population.
A major problem in cities due to immigration from high incidence areas.
What are some statistics about TB?
Number 1 killer of communicable diseases.
2 billion infected worldwide.
2/3 of cases in 8 countries / born abroad.
7/8 of cases in 30 countries.
What groups in the UK are vulnerable to TB?
Those from high prevalence countries.
Most are aged 15-44.
HIV positive, immunosuppressed, elderly, neonates, diabetics, homeless, alcohol dependent, IVDU, prisons.
What are mycobacteria?
Ubiquitous in the soil and water.
Non-motile bacilli that are slow growing.
The disease is slow, but treatment is long.
Aerobic (predilection for lung apices).
AAFB (not all AAFBs are TB).
What is unique about mycobacteria?
A very thick fatty cell wall.
Resistant to acids, alkalis, and detergents.
Resistant to neutrophil and macrophage destruction.
How is TB transmitted?
Airborne - pulmonary and laryngeal TB.
Droplet spread - suspended in air.
Prolonged close contact.
Eliminated by UV and dilution.
Unpasteurised infected cows’ milk (M. Bovis, uncommon in the UK).
How does central caseating necrosis occur in TB?
Activated macrophages form epithelioid cells, which form Langhan’s giant cells.
These cells accumulate and form a granuloma.
Necrosis occurs and may later calcify.
What is the natural history of TB?
Primary infection.
Mycobacteria spread via lymphatics to draining hilar LNs.
Usually no symptoms (fever, malaise).
Erythema nodosum (swollen fat under the skin).
Chest signs (rare).
Associated with tuberculoprotein immunity.
What are the symptoms of TB in the majority of people?
An initial lesion and local lymph node.
May scar or calcify (Ghon focus - radiographic finding on a chest, consisting of scar tissue and consolidation. Significant for TB).
How can primary infection of TB develop into tuberculous bronchopneumonia?
Primary focus enlarges into a cavity.
Enlarged hilar LNs compress bronchi (poor prognosis - the lobar collapses and LN discharges into bronchus).
A small number of patients.
How can primary infection of TB develop into miliary TB?
Looks like millet seeds on autopsy.
Haematogenous spread of bacteria to multiple organs.
Fine mottling on CXR, widespread small granulomata.
CNS TB in 10-30%.
A small number of patients.
What is the post-primary disease of TB?
Only occurs in humans.
TB may enter a dormant stage with low or no replication over prolonged periods of time.
A balance between replication and destruction by immune mechanisms occur.
What are the stages of TB?
Primary complex (85%).
Progressive primary disease (1%).
Miliary, meningeal, or pleural TB - 6-12 months.
Post-primary disease - 1-5 years (typically).
Genitourinary and cutaneous TB - 1-15 years (typically).
What is the clinical presentation of TB?
Cough.
Fever, night sweats, weight loss.
Each symptom was absent in 40%.
All three absent in 25%.
CRP normal in 15%.
ESR normal in 21%.
How can you diagnose post-primary TB?
Classical - fluffy or nodular upper zone, cavitation in 10-30%.
Rare - lymphadenopathy.
CXR is normal in 13% of definitive pulmonary TB (22% in HIV).
