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
What TB drug can affect hormonal contraception
Rifampicin
Rifampicin side-effects
Discolours urine and bodily fluids orange
Ethambutol side-effects
Optic neuritis
Types of TB drug resistance
Multi-drug resistance (MDR) - Rifampicin and Isoniazid Extensive drug resistance (XDR) - MDR + quinolone and injectable Usually seen in russian states
What test should always be done for TB
HIV as it might be a co-infection
How does latent TB show on x-rays
No symptoms however there may be granulomas or calcification left over.
Tests for previous exposure to TB antigen
Blood - Interferon gamma release assay (IGRA)
Skin - Mantoux (tuberculin) test
Drawback of mantoux test
Cannot distinguish between latent, cured, active TB and BCG
Why does mantoux test involve 48 hours wait
Reaction to Mycobacterium is a type 4 hypersensitivity (delayed) reaction. Hence, we wait and see
What is Mantoux test also known as
Tuberculin Skin Test (TST)
Drawbacks of tuberculin skin test (TST)
Operator dependant and low sensitivity. Reaction is also diminished in immunocompromised individuals
Management of latent TB
Best left alone however can give drugs -
6 months of Isoniazid or
3 months of Rifampicin and Isoniazid combination
6 months Isoniazid vs 3 months Rifampicin + Isoniazid
6 months is with one drug but longer whereas 3 months involves two drug; more side-effects
What should be screened for before starting anti-TNF drugs
TB as anti-TNF drugs can reactivate TB
How is BCG related to TB
BCG is an attenuated strain of Mycobaterium bovis
How can TB be prevented
Contact tracing to identify cases, screening of high risk subgroups, isolate infectious cases, BCG immunisation, social measures
HIV and TB
All TB cases should be offered an HIV test
All HIV cases should be offered a chest x-ray
Steroids and TB
Steroids and other immunosuppresant drugs can reactivate TB
