Microbiology - TB + Mycobacteria Flashcards
What is a Gohn focus?
- A tuberculous caseating granuloma (tuberculoma) seen in upper/mid zones
- Pulmonary TB
What is a Gohn comlpex?
- Gohn focus
- Lymphadenopathy
What is a RF for symptomatic primary TB infection?
Immunocompromised
What is the process of getting TB?
- Exposure
- Can become infected or non-infected
- IF infected can have primary TB symptoms, leading to latent TB, or just have latent TB
- Latent TB is asymptomatic, but can have Gohn focus + granuloma
- Can have no reactivation (asymptomatic) or reactivation (symptomatic)
What is a classic lesion of TB?
Caseating granuloma
What are some RFs of developing TB?
- Travel (South Asia/Eastern Europe)
- HIV +ve
- Homeless
- IVDU
- Contact
What are some general symptoms of TB?
FLAWS
What are some respiratory symptoms of TB?
- Haemoptysis
- Cough
What are some less common presentations of TB (seen in immunocompromised)?
- Subacute meningitis
- Pott’s Disease (spinal)
- Miliary TB
What are some symptoms of subacute meningitis and how is it caused from TB?
- TB infiltration into brain
- Headaches
- Personality changes
- Meningism
- Confusion
What are some symptoms of Pott’s disease (secondary to TB)?
- Back pain
- Vertebral destruction
- Iliopsoas abscess
What is a sign of miliary TB (seen on CXR)?
Disseminated haematogenous spread
- Miliary seed appearance
What are some investigations used to diagnose TB and the results?
- CXR: Upper lobe cavitation
- Sputum samples (X3): Ziehl-Neelson stain (culture on Lowenstein-Jensen medium for 6/52) shows acid-fast bacilli
- Tuberculin skin etsts (Mantoux/Heaf) - shows exposure (inc. BCG)
- IGRA (Elispot/Quantiferon) - shows exposure (exc. BCG)
What is the gold standard investigation for diagnosing TB?
Ziehl-Neelson stain
What is the first-line treatment for TB?
RIPE
- Rifampicin
- Isonazid
- Pyrazinamide
- Ethambutol
All 4 for 2 months, first two for 4 months
What are some side effects of the RIPE treatment for TB?
- Rifampicin: orange secretions
- Isonazid: peripheral neuropathy
- Pyrazinamide: Hepatotoxic, hypercalciuraemia
- Ethambutol: optic neuritis
What medication can be given to prevent peripheral neuropathy as a result of isonazid treatment in TB?
Pyridoxine (Vitamin B6)
What are some second line treatments for TB?
Injectables
- Amikacin
- Kanamycin
- Quinolones
- Linezolid
What treatment is given as prophylaxis or for latent TB?
Isonazid monotherapy (6/12)
What is the mechanism of action of rifampicin?
Inhibits RNA polymerase
What is the mechanism of action of isonazid?
Decreased mycolic acid synthesis (in cell wall)
What is the mechanism of action of ethambutol?
Decreased polymerisation in cell wall
What is the vaccine to prevent TB?
BCG - Bacille-Calmette-Guerin
- Attenuated strain of M. bovis given to high risk pts
- CI: Immunosuppresion
What is seen in paucibiliary tuberculoid leprosy?
- Few skin lesions
- Hairless plaques
- Loss of sensation
- Robust T cell response
What is seen in multibacillary lepromatous leprosy?
- Multiple skin lesions
- Poor T cell response
- Thickened dermis
- Lion-like face
What is generally seen in leprosy?
- Skin depigmentation
- Nerve thickening
- Nerve damage (invades schwaan cells + histiocytes)
- Trophic ulcers + nodules
What is the cause of leprosy and some RFs?
RFs:
- >65yrs
- Immunosuppression
- Environmental exposure (water/soil)
Cause: M. leprae
What are some featurese of Mycobacterium avium-intracellulare complex?
- Disseminated infection in immunocompromised
- Resembles TB if underlying disease
- Found in soil, food + water
- Slow growing
What are some features of Mycobacterium Marinarum (fish tank granuloma)
- Swimming pool granuloma (aquarium owners)
- Plaques/papules
What are some features of Mycobacterium ulcerans (Buruli ulcer)?
- Tropics/Australia
- Painless nodules progressing to ulceration (Bairnsdale + Burule)
- Scarring + contractures
- Insect transmission (bite)
- Slow progression
