Tuberculosis Flashcards
Common causative organisms of tuberculosis
Mycobacterium tuberculosis or Mycobacterium bovis
Pathology of TB
Primary TB - Inhaled organism is phagocytosed and carried to hilar lymph nodes. Immune activation leads to granulomatous response in nodes usually killing of organism.
Secondary TB - Reactivation of disease which tends to remain localised often in apices of lungs. Can spread via airways or bloodstream
Time period of primary TB
1st exposure and upto 5 years afterwards
Tissue changes in TB
Primary - Ghon focus (small lesion in pleural cavity) in periphery of mid zone of lungs. Large hilar nodes (granulomatous)
Secondary - Fibrosing and cavitating apical lesion with caseous necrosis
What is a ghon focus
A small lesion in pleural space caused by Mycobacterium tuberculosis. It is a granulomatous inflammation.
What stain is used to identify TB causing organism
ZIehl-Neelsen stain
What can secondary TB lead to
Miliary TB which is widespread dissemination of Mycobacterium tuberculosis via hematogenous (via blood) spread. It involves millet like seeding of TB bacilli in lungs.
Why does TB get reactivated
Decrease T cell function due to -
Age, immunosuppression (steroids, cancer, chemotherapy), immunodeficient (HIV)
Reinfection at high dose or more virulent organism
What is bronchoalveolar lavage (BAL)
A medical procedure in which a bronchoscope is inserted through the mouth or nose into lungs and fluid is squirted into a small part of the lungs. This is examined and useful in diagnosing lung disease
What causes pneumocystis pneumonia (PCP)
Caused by yeast-like fungus called Pneumocystis jirovecii. Found in immunocompromsied hosts
A young African man presents with a cough and night sweats. His chest x-ray shows dense consolidation in the right upper lobe with cavity formation.
This is Tuberculosis
How does Mycobacterium tuberculosis spread
Air
What happens after exposure to TB
Mycoplasma tuberculosis infects phagoctyes such as macrophages and neutrophils. Granulomas are formed to wall off the pathogen. However this can be a growing collection of cells for the pathogen to infect and replicate within. Most time the granulomas sustain and the infection is dealt with. However, it may burst causing the pathogen to travel around
Clinical features of TB
Weight loss, malaise, night sweats, cough, haemoptysis, breathlessness, upper zone crackles
What are cold abscess
Collection of pus without the pain and acute inflammation seen in conventional abscess
Why should steroids not be injected into solitary arthritic joint
It might be tuberculosis
What stain is used in TB
Ziehl-Neelsen stain
How long is TB sputum sample cultured for
12 weeks as this might pick up additional culture positive cases who will need treatment but not infectious due to tiny number of pathogens
What does positive PCR for TB indicate
Patient may have had the disease previously
What cells are seen under microscope in TB
Multinucleate giant cells - Mass formed by union of several distinct cells (cells of macrophage lineage fused together). Often form a granuloma
How does TB heal
With calcification, often leave scar tissue
Where does TB usually affect lungs
Upper lobe predominance. Lung cancer/pneumonia often affects middle/lower lobe
TB that resembles the appearance of millet seeds
Miliary TB, massive seeding of TB through the bloodstream which can lead to rapid fatality
Therapy for TB
2 months of -
Rifampicin, Isoniazid, Pyrazinamide, Ethambutol
Then 4 months of -
Rifampicin, Isoniazid
