Saturday, 30 October 2010

MRCP revision battle 37.1: TB

Today has a respiratory feel....

MRCP revision battle 37.1: TB
MRCP revision battle 37.2: DVT/PE in pregnancy
MRCP revision battle 37.3: Asthma
MRCP revision battle 37.4: Cor pulmonale
MRCP revision battle 37.5: alpha-1 antitrypsin deficiency
MRCP revision battle 37.6: Cystic fibrosis
MRCP revision battle 37.7: HPOA

MRCP revision battle 37.1: TB

TB is an infection caused by mycobacterium tuberculosis.  Primary infection is usually in the lungs (ghon focus, usually in the mid or lower zones).  Second favourite site for primary infection = GI, ileocaecal area.

Incidence =7000/yr in UK

Spread is by droplet infection. Household contacts have 1 in 4 chance of infection therefore contact tracing is very important and TB is a notifiable disease.

Primary TB is often symptomless. Although it may cause fever, sweats, anorexia, cough or erthyema nodosum.  If the immune system ‘wins’, the TB is walled off by calcification; however, the TB remains active in ~ 20% calcified areas and may be reactivated when immune system is weakened, eg steroids, diabetes, HIV.

Post-primary TB makes you ill – fever, malaise, weight loss, anorexia, tiredness, cough, haemoptysis, rarely night sweats.

 It can spread to:
  • brain = meningeal TB
  • spine = Potts fracture
  • blood = miliary
  • skin = lupus vulgaris

•    CXR
•    Sputum cultured/stained with Zielh-Nielsen – looking for acid-fast bacilli
•    Mantoux test of little help in the UK due to BCG

BCG = bacilli calmette-guerin – decreases risk of TB by 50%

Treatment: DOTS
•    2 months rifampicin, isoniazid, pyrazinamide and ethambutol (=RIPE)
•    then 4 months rifamicin and isoniazid
•    Pyridoxine throughout to protect against neuropathic effects of isoniazid

MRCP (and real life) side effects of TB meds to be aware of:

Rifampicin turns bodily excreations orange
Isoniazid and rifampicin cause cirrhosis – check LFTs
Pyrazinamide decreases urea excreation = risk of gout and CI in gout sufferers
Ethambutol can affect the optic nerve - check colour vision

On to DVT and PE in pregnancy...