Tuberculosis

Question 1

What are the causative pathogens of tuberculosis?

Answer 1

• Most common cause is mycobacterium tuberculosis
  
  • Rod shaped bactera - a bacillus
  • Waxy coating making gram staining ineffective
  • Resistant to the acids used in staining - acid-fastness
  • Require special staining with Zeihl-Neelsen stain that turns up bright red on a blue background
• Other causes include:
  
  • Mycobacterium bovis
  • Mycobacterium kansaii
  • Mycobacterium chelonae
  • Mycobacterium abscessus
  • Mycobacterium fortuitum
  • Mycobacterium leprae

Question 2

What is the immune response to tuberculosis?

Answer 2

• Intracellular pathogen so isn’t affected by antibodies
• Cytokine IFN gamma responsible for activating macrophages to keep TB under control
• APC and bacillus invade cell, bacterial proteins in cytoplasm presented to APC MHC class II, T cells recognise these and start to proliferate, driven by IL-12 and IL-18

Question 3

How is tuberculosis diagnosed?

Answer 3

• Zeihl Neelsen stain used as resistant to being washed with acid or alcohol solution
• Mantoux reaction (purified M. Tb proteins injected, APC’s engulf them and a nodule forms)
• T-Spot test similar to Mantoux but in a test tube, blood added to test tube with Tb proteins, if exposed before IFN gamma will be produced and capture antiboties in test tube, colour change occurs)
• In patients with active TB CXR and culture are used to support diagnosis

Question 4

How is tuberculosis treated? (RIPE>RIP>RI)

Answer 4

• Management of latent TB
  
  • Rifampicin and Izoniazid for 3 months
  • Izoniazid for 6 months
• Management of active TB
  
  • Rifampicin and Izoniazid for 6 months
  • Pyrazinamide and Ethambutol for 2 months
• Izoniazid causes peripheral neuropathy and so pyridoxine (vitamin B6) is commonly proscribed alongside it

Question 5

BCG vaccination

Answer 5

• Intradermal infection of live attenuated (weakened) TB - offers protection against severe and complicated TB but less effective against pulmonary TB
• Prior to vaccine tested with Mantoux test - vaccine only given if test is negative
• Patients also assessed for possibility of HIV and immunosuppression due to risks related to a live vaccine
• Offered to patients at higher risk of contact with TB
  
  • Neonates born in areas of UK with higher rates of TB
  • Neonates with relatives from countries with high rates of TB
  • Neonates with a FHx of TB
  • Unvaccinated older children and young adults (<35) who have close contact with TB
  • Unvaccinated children and young adults tat recently arrived from countries with high rates of TB
  • Healthcare workers

Question 6

Presentation of TB

Answer 6

• Usually chronic, gradually worsening symptoms
• Typical signs include:
  
  • Lethargy
  • Fever or night sweats
  • Cough with or without haemoptysis
  • Lymphadenopathy
  • Erythema nodosum
  • Spinal pain in spinal TB (also known as Pott’s disease of the spine)

Question 7

Side effects of Rifampicin (remember ‘red-an-orange-pissin’)

Answer 7

• Red/orange discolouration of secretions like urine and tears
• Potent enzyme inducer of cytochrome P450 and so reduces effect of drugs metabilised by this system - important for medications like the COCP

Question 8

Side effects of Isoniazid (rememer ‘I’m-so-numb-azid’)

Answer 8

• Peripheral neuropathy
• Pyridoxine (vitamnin B6) often prescribed alongside to reduce the risk

Question 9

Side effects of Pyrazinamide

Answer 9

• Hyperuricaemia resulting in gout

Question 10

Side effects of Ethambutol (remember ‘eye-thambutol’)

Answer 10

• Colour blindness
• Reduced visual acuity

Question 11

Side effects of Rifampicin, Isoniazid and Pyrazinamide

Answer 11

• Hepatotoxicity