Tuberculosis (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 is in the GI tract, especially the ileocaecal area.
Patients with TB infections in locations other than the lungs are rarely infectious to others.
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, haemopytsis 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.
TB of GI tract may present like acute appendicitis or with acute/subacute obstruction. It may also cause GI bleeding.
TB can spread to:
- brain = meningeal TB – commonest nerve palsies = 3rd and 6th
- spine = Potts fracture
- blood = miliary
- skin = lupus vulgaris
Diagnosis of TB is by:
- Sputum cultured/stained with Zielh-Nielsen – looking for acid-fast bacilli
- Mantoux test of little help in the UK due to BCG. Also false negatives occur if patient’s immune system is depressed, eg HIV or on steroids
- blood – interferon-gamma test
BCG vaccine (bacilli calmette-guerin) decreases risk of TB by 50%. It is a live vaccine. No longer done routinely at school.
Treatment of TB:
- 2 months rifampicin, isoniazid, pyrazinamide and ethambutol (=RIPE)
- then 4 months rifamicin and isoniazid
- Pyridoxine throughout to protect against neuropathic effects of isoniazid
- If meningeal TB, add in a glucocorticoid.
Most patients are no longer infectious after 2 weeks treatment.
Those with multiple resistant TB require longer treatment – up to 24 months – and their infectious period is longer.
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
Small print gem: BCG vaccine also provides up to 60% efficacy against leprosy and Buruli ulcer, which are caused by other mycobacterium.