Tuberculosis Flashcards
What are the risk factors for tuberculosis?
Diabetes
Immunosuppressed
Alcohol
Poor social circumstances/malnourished
Immigrant/overseas travel
HIV
What organisms cause TB?
Mycobacterium tuberculosis
Mycobacterium bovis
How is mycobacterium tuberculosis spread?
Air-borne transmission
How is mycobacterium bovis spread?
Un-pastered milk
How is miliary tuberculosis spread?
Haematogenous spread of tubercle bacilli through the pulmonary venous system
Describe the presentation of TB
Haemoptysis
Persistent cough with grey sputum production
Weight loss
Dyspnoea
Lethargy
Night sweats
Fever
Erythema nodosum
What area of the lung does TB favour?
Upper lobes
What investigations are used in TB diagnosis?
CXR
Sputum culture with Zeil Neilson stain
- 3+ on successive days
Bronchoscopy and biopsy for histology with Zeil Neilson stain
What investigations are used in TB monitoring?
Visual acuity: Optic neuritis due to Ethambutol
LFT: Liver failure
U&E: Renal failure
What CXR findings are present in TB?
Bilateral hilar lymphadenopathy
Upper lobe cavitation
Millet seeds in miliary TB
What is the management of TB?
RIPE
Rifampicin
Isoniazid
Pyrazinamide
Ethambutol
All for 2 months, then first 2 for 4 more months
What are the side effects of Rifampicin?
Orange urine
Hepatitis
It is a potent inducer of cytochrome P450 enzymes therefore reduces the effect of drugs metabolised by this system, such as COCP
What are the side effects of Isoniazid?
Peripheral neuropathy
Hepatitis
Agranulocytosis
What are the side effects of Pyrazinamide?
Gout
Hepatitis, most commonly
What are the side effects of Ethambutol?
Optic neuritis
What is given to prevent peripheral neuropathy caused by Isoniazid?
Pyridoxine
What is multi-drug-resistant TB (MDR-TB)?
Resistance to rifampicin and isoniazid
Teatment is complicated and must be done under specialist centres, usually involving five or more drugs to which the bacteria is susceptible for a minimum of 9 months
What investigation should be offered to all TB patients?
HIV testing
Why are LFTs measured prior to and during TB therapy?
Rifampicin, Isoniazid and Pyrazinamide can call cause hepatitis
What drug is given to prevent Ethambutol associated optic neuritis?
Pyridoxine
What is the mechanism of action of Rifampicin?
Inhibits bacterial DNA dependent RNA polymerase preventing transcription of DNA into mRNA
What is the mechanism of action of Isoniazid?
Inhibits mycolic acid synthesis
What is the mechanism of action of Pyrazinadmide?
Converted by pyrazinamidase into pyrazinoic acid which in turn inhibits fatty acid synthase (FAS) I
What is the mechanism of action of Ethambutol?
Inhibits the enzyme arabinosyl transferase which polymerizes arabinose into arabinan
What causes peripheral neuropathy with Isoniazid?
B6 deficiency
What type of bacteria is mycobacterium tuberculosis?
acid-fast bacilli
Meaning they are rod shaped and resistant to the acids used in staining procedures, so require ZN stain
What colour does mycobacterium tuberculosis turn with ZN stain?
Red against blue background
What are the classifications of TB?
Active, where infection is active in various areas of body
Latent, in which immune system encapsulates site of infection and stops disease progression
Secondary, when latent TB reactivates
Disseminated/Miliary, in which immune system is unable to control disease
Extrapulmonary, in which TB affects other areas
What can cause a false negative Mantoux test?
Immunosuppression/steroids
Sarcoidosis
Lymphoma
Extremes of age
Fever
Hypoalbuminaemia
Anaemia
What investigation is used to identify latent TB?
Interferon gamma release assay (IGRA)
Give features of aspergilloma
Fungus arising secondary to TB, lung cancer, CF
Cough
Haemoptysis
Rounded opacity with crescent sign on xray
