Tuberculosis Flashcards
Is the disease burden from TB increasing or decreasing?
It is falling globally
How bad is the TB epidemic?
- TB is the number 1 killer of communicable diseases.
- TB kills more than HIV and Malaria together.
What are the vulnerable groups in the UK for TB?
- Those from high prevalence countries.
- Homeless, alcoholics, IDU’s, those with mental health problems and in prison.
- HIV positive, Immunosuppressed.
- Elderly, neonates, diabetics.
Which mycobacteria can cause TB?
- M. tuberculosis, M. africanum, M. bovis.
- They are non-motile bacillus, very slow growing and aerobic.
- Uniquely has a very thick fatty cell wall.
- HOWEVER, not all acid and alcohol fast bacilli (AAFBs) are TB.
How is TB transmitted?
- Airborne (pulmonary & Laryngeal TB spreads, the others not)
- Usually requires prolonged close contact.
- Outdoors mycobacteria is eliminated by UV radiation and dilution.
What is the exception to the rule about hoe TB is spread?
- Exception is Mycobacterium bovis, which can be spread by consumption of unpasteurized infected cows’ milk (very uncommon in the U.K.)
Immunopathology (immune responses) for TB
Activated macrophages > Epithelioid cells > Langhan’s giant cells
Accumulation of macrophages, epithelioid & Langhan’s cells > GRANULOMA
Central caseating necrosis (may later calcify)
How is the Th1 cell mediated immunological response like a two edged sword?
- It eliminates/ reduces number of invading mycobacteria.
- Tissue destruction is a consequence of activation of macrophages.
Features of primary infection of TB
- No preceding exposure or immunity.
- Mycobacteria spread via lymphatics to draining hilar lymph nodes.
- Usually no symtoms, can be fever, malaise.
What does the primary infection progress to (in a small number 1%)?
It progresses to Tuberculous bronchopneumonia.
- Primary focus continues to enlarge - cavitation
- Enlarged hilar lymph compress bronchi, lobar collapse
- Enlarged lymph node discharges into bronchus
What does the primary infection progress to (in a small number 1-3%)?
- Miliary TB (looked like millet seeds on autopsy) develops, with hematogenous spread of bacteria to multiple organs
- Fine mottling on X-ray, widespread small granulomata
- CNS TB in 10-30%
What does the primary infection progress to (in the majority >85%)?
- Initial lesion + local lymph node (Primary complex)
- Heals with or without scar. May calcify (Ghon focus + complex)
- Associated with development of immunity to tuberculoprotein
What are the two main hypothesis’ of post primary disease?
- TB bacteria entering a dormant stage with low or no replication over prolonged periods of time.
- Balanced state of replication and destruction by immune mechanisms.
What are the clinical presentations of TB?
- Cough
- Fever
- Sweats (mainly at night)
- Weight loss
- All three symptoms
- CRP normal in 15%, ESR normal in 21%.
What may be absent in the clinical presentations of TB?
- Fever absent in 37%
- Sweats absent in 39%
- Weight loss absent in 38%
- All three absent in 25%
When would you consider CT post-primary TB?
- Normal Chest Xray but clinical suspicion
- Miliary TB
- Cavitation & other differential
- Lymphadenopathy, alternative diagnosis.
- Targets for BAL
How would you diagnose active pulmonary TB using Chest Xray?
Primary TB:
- Mediastinal lymphadenopathy (mainly unilateral, 15% bilateral)
- Pleural effusion
- Miliary (hematogenous spread, 1-3%)
- Pneumonic lesion w/ enlarged hilar nodes- consider primary TB
How would you get a bug sample for TB?
- Sputum; 3 samples, 8-24hrs gap, at least 1 early morning sample
- Induced sputum
- Bronchoscopy with BAL
- Endobronchial ultrasound (EBUS) with biopsy
- Lumbar puncture in CNS TB
- Urine in urogenital TB
- Aspirate/biopsy from tissue ( lymph-node, bone, joint, brain, abscess …)
- Mantoux or IGRA are NOT routinely used in diagnosing active TB
What drugs are used to treat TB?
- Streptomycin
- Isoniazid
- Pyrazinamide
- Rifampicin
- Ethambutol
Rules for the treatment of tuberculosis
- Multiple drug therapy is essential
- Single agent treatment leads to drug resistant organisms within 14 days.
- Therapy must continue for at least 6 months.
- TB therapy is a job for committed specialists only.
- Legal requirements to notify all cases.
- Test for HIV, Hepatitis B and C.
What is the standard treatment for TB?
2 Rifampicin/Isoniazid/Ethambutol + 4 Rifampicin/Isoniazid
- Standard 70kg patient takes 12 tablets daily.
- 6 months duration
- Pyridoxine (Vitamin B6) with isoniazid to reduce risk of neuropathy
- Steroids (CNS, Milliar, Pericardial)
- Vitamin-D substitution ?
What are side effects of Rifampicin?
- Orange ‘Irn Bru’ urine/tears/lenses
Induces liver enzymes, prednisolone, anticonvulsants - All hormonal contraceptive methods ineffective
- Hepatitis
What are the side effects of Isoniazid?
- Hepatitis
- Peripheral neuropathy (pyridoxine B6)
Who can get the BCG vaccination?
- Given selectively to risk groups since 2005
- Neonates, or unvaccinated children under 5, whose parents/grandparents were born in a country with an annual incidence of TB of 40/100,000 or greater
- Unimmunised contacts of cases
- Unimmunised high risk employees
