Tuberculosis Flashcards
What is tuberculosis?
Bacterial infection affecting the lungs
What organism causes tuberculosis in humans?
Myobacterium tuberculosis
What are the characteristics of mycobacterium?
Non-motile
Very slow growing
Aerobic
Very thick cell wall - lipids, peptidoglycans, arabinomannans
Resistant to neutrophil and macrophage destruction
How is TB transmitted?
coughing, sneezing, respiratory droplets
Myobacterium bovis - consumption of infected cow’s milk
Describe the pathophysiology
When mycobacterium gets into alveoli, macrophages endocytose them. Antigen presenting cells (the macrophages) migrate to lymph nodes and present antigen to T helper cells. Clonal proliferation of Th1 cells specific to the antigen occurs. These go back to alveoli and reaction activates macrophage to allow it to now kill the TB organisms. The problem is, as body kills off TB organisms this causes
Tissue damage occurs as the activated macrophages turn into epithelioid cells which accumulate to form Langhan’s giant cells. They all form a granuloma leading to central caseating (cheese) necrosis, which can later calcify (coin shapes).
Risk factors
HIV overcrowding poverty malnutrition race, age, immunosuppression diabetes mellitus
What are the different types of TB (in order chronologically when they would be likely to occur)
Primary infection Progressive primary infection Miliary, Meningeal or Pleural TB Post primary infection (pulmonary, skeletal) Genitourinary, cutaneous TB
Primary infection symptoms and signs
Usually none
Fever
Malaise
Erythema nodosum (red lumps on lower legs)
What are the three possible outcomes of primary infection?
Progressive disease
Contained latent
Cleared cured
What happens in progressive primary infection?
Primary focus continues to enlarge - cavitation
Enlarged hilar lymph compress bronchi, lobar collapse
Enlarged lymph node discharges into bronchus
Tuberculous bronchopneumonia
What is miliary TB?
Widespread granuloma - fine mottling on x-ray
Features of meningeal TB
severe
CSF high protein, lymphocytes
2 possible causes of post primary disease
- reactivation of mycobacterium from latent primary infection disseminated by the blood stream around the body
- New re-infection from outside source, susceptible previously infected host
Symptoms of post primary disease
cough sputum haemoptysis pleuritic pain breathlessness malaise fever weight loss
signs of TB
only if more advanced:
crackles, bronchial breathing
