Tuberculosis Flashcards
What causes TB
mycobacterium tuberculosis
What is primary tb?
when a non-immune host who is exposed develops primary infection in the lung
What is a ghon complex?
combination of a ghon focus (lung lesion) and lymph node
what is a ghon focus composed of?
tubercle-laden macrophages
What is the usual natural history of primary TB in immunocompetent?
initial lesion usual heals by fibrosis
What usually happens to ghon focus in immunocompromised?
may develop disseminated disease - military tb
What is secondary tb
a host who has had the infection before (either asymptomatically or had it and recovered) becomes immunocompromised and the initial inf is reactivated
What are causes of being immunocompromised and getting secondary tb?
immunosuppressive drugs - steroids
HIV
malnutrition
Where does reactivation usually occur in secondary tb?
apex of the lungs
can then spread locally or to more distant sites
what is the most common site for secondary tb?
lungs
Where may extra-pulmonary infection occur?
CNS - tuberculous meningitis Vertebral bodies - Potts disease Cervical LN - scrofula renal - sterile pyuria GI tract hepatitis
What is the main test for latent tb? give an alternative
Mantoux test
interferon-gamma blood test
What result of the test for latent tb suggests tb infection?
induration of >15mm
What result of the test for latent tb suggests previous TB infection or BCG
6-15mm
What does a result of <6mm in the TB test mean?
that there is no significant hypersensitivity to the tuberculin protein
What may cause a false negative Mantoux test?
military TB sarcoidosis HIV lymphoma young age <6m
When would a smaller induration be expected in the Mantoux test?
if they have HIV or are immunosuppressed due to reduced ability to develop a hypersensitivity response
What is involved in the Mantoux test?What is highly suggestive of TB?
A positive test w a prev BCG vaccination
What is the difference between tb infection and diseasE?
infection - latent, not contagious and not sick
disease - active, immune system overcome by TB
What are RF for developing active TB
silicosis chronic renal failure HIV organ transplant w immunosuppression IV drug use haematological malignnayc anti-tnf treatment
explain the histological changes in tb when a lung lesion forms
ghon focus -> granuloma (collection of epithelioid histiocytes) -> caseous necrosis in the centre
How is a diagnosis of TB made?
Sputum sample - x3 acid fast bacilli
CXR - cavity, pleural effusion, lymphadenopathy, parenchymal infiltrates mainly in apexes
What are symptoms of TB w pulmonary involvement
persistent productive cough
breathlessness
haemoptysis
What are symptoms of systemic TB?
general: weight loss fever night sweats anorexia malaise
What sx suggest extra pulmonary involvement?
lymphadenopathy bone, joint, back pain abdo pelvic pain constipaiton sterile pyuria Headache vomiting irritability confusion Skin lesions - erythema nodosum
wHAT ARE sx in children of systemic TB
Faltering growth
reduced energy
persistent fever
What is the standard therapy for active TB?
Initial phase (2m): 1. Rifampicin 2. Isoniazid 3. Pyrazinamide 4. Ethambutol Then continuation phase: - Rifampicin - Isoniazid
What is the treatment for latent tb?
For 3m: 1. Rifampicin 2. Isoniazid 3. Pyridoxine OR For 6m: 1. Isoniazid 2. Pyridoxine
What is the treatment for meningeal TB?
Treat for at least 12m w addition of steroids
What groups of people require directly observed therapy w three times a week dosing regimen?
homeless people with active tuberculosis
patients who are likely to have poor concordance
all prisoners with active or latent tuberculosis
what are SE of rifampicin?
potent liver enzyme inducer
hepatitis
orange secretions (urine)
flu like sx
What are SE of isoniazid
peripheral neuropathy (prevented w pyridoxine) vit b6
hepatitis, agranulocytosis
liver enzyme inhibitor
What are SE of pyrazinamide?
hyperuricaemia -> gout
arthralgia
hepatitis
What are SE of ethambutol? what ix does this prompt before starting and during rx?
optic neuritis - check visual acuity
How does TB appear on Ziehl-Neelsen stain?
bright red
Where do ghon complexes usually occur?
in the lower lobes of the lungs
How does a ghon complex appear on XR?
as calcification known as a ranke complex
Why do bacteria spread to upper lobes in secondary infection?
greatest area of oxygenation and the bacteria are strict aerobes
