Tuberculosis Flashcards
(30 cards)
what bacteria causes TB?
myobacterium tuberculosis
where is TB common?
B is endemic to many parts of Asia, Africa, South America and eastern Europe and was common in the UK until the 1950s
what is the pathogenesis of TB?
Transmitted by aerosol inhalation and causes pulmonary infection, then
spreads via haematogenous spread to any site in the body.
Initial infection can be asymptomatic. Can lie dormant for many years without causing symptoms (latent TB), then reactivate later in life to form active infection.
It is common for people immigrating to the UK from endemic areas to experience reactivation after their arrival.
The exact reason for this is unknown. Vitamin D deficiency is being researched as a cause.
what is the lifetime reactivation risk of TB?
Lifetime reactivation risk is estimated at 10-15% (Usually due to immunosuppression, advancing age, or HIV infection)
how can TB be classified?
TB can be classified as active or latent. Active TB is then classified by the site affected (pulmonary, pericardial, abdominal, miliaryetc)
what is latent TB`?
By definition, latent TB is asymptomatic and is identified by screening
screening involves CXR and measurement of interferon gamma (quantiFERON or T spot)
what is quantiFERON?
Assesses the amount of interferon gamma released by T cells when they are exposed to proteins found on mycobacteria.
Pre-exposed cells release more interferon
It does not differentiate between active and latent TB.
It is not used to diagnose active TB and can also be negative during infection.
Patients with immunosuppression may not release interferon gamma causing false negatives.
what is the T spot test?
similar principle to quantiFERON test, but rather than testing whole blood the lymphocytes are isolated and tested directly.
Theoretically meaning if there is a deficiency of lymphocytes the quantiFERON might be indeterminate but the t spot may be positive.
A POSITIVE INTERFERON GAMMA TEST DOES NOT MEAN THE PATIENT HAS ACTIVE TB AND A NEGATIVE INTERFERON GAMMA TEST DOES NOT MEAN THAT A PATIENT DOESN’T HAVE ACTIVE TB
who is screened with interferon gamma tests?
used in asymptomatic patients with risk factors for latent TB:
- Immigrants from high prevalence countries
- Healthcare workers
- HIV positive patients
- Patient starting on immunosuppression
how is latent TB treated?
3 months rifampicin and isoniazid or 6 months rifampicin alone
- Treatment reduces risk of reactivation needs to be balanced against the risk of
hepatotoxicity. - Pts aged > 35 are at increased risk of hepatotoxicity. Current guidelines advise against treating latent TB in these patients unless they have other risk factors (HIV or work as a healthcare worker).
what are the common symptoms of active TB?
- non resolving cough
- unexplained persistent fever
- drenching night sweats
- weight loss
what imaging can be done into active TB?
CXR: Mediastinal lymphadenopathy or a cavitating pneumonia or pleural effusion among other signs
CT: Lymphadenopathy. Nodes with central necrosis are more suggestive.Lesions in viscera can also be seen
MRI – can show leptomeningeal enhancement in TB meningitis
what is the gold sample culture for diagnosis?
Culturing the bacteria is the gold standard for diagnosis
If possible treatment should be delayed until adequate samples have been taken
Culture can take 6 weeks so ATT (Ethambutol, Pyrazinamide, INH, Rifampicin) is usually started after samples taken
how is pulmonary TB identified?
sometimes can be identified from sputum samples or induced sputum (sputum taken after a nebuliser of 7% hypertonic saline).
If TB can be seen on a sample using simple microscopy it is said to be ‘smear positive’. This implies a high bacterial load and high infectivity. ATT can be started immediately as there is a high chance it will culture.
If a sputum sample is ‘smear negative’ then we usually proceed to bronchoscopy +/- EBUS (endobronchial ultrasound guided biopsy) of pulmonary lymph nodes.
Once these samples are taken we start ATT
how is meningeal TB identified?
lumbar puncture for TB culture and TB PCR
how is lymph node TB identified?
core biopsy of lymph node (FNA is not adequate)
how is pericardial TB identified?
ideally pericardiocentesis – often not practical
how is GI TB identified?
colonoscopy and bowel biopsy/ Ultrasound guided omentum biopsy
what can be seen on histology of tissue affected by TB?
caseating/necrotising granulomatous inflammation
why do TB symptoms get worse a the start of treatment?
Increase in inflammation as bacteria die causing worsening symptoms. Usually occurs at the start of treatment
paradoxical reaction
if TB is affecting sites where additional swelling cannot be tolerated (e.g. meningeal/spinal/pericardial TB) what can be given to help?
steroids can be given at the start of treatment
paradoxical reaction as giving ATT treatment straight away can make it worse
what are the features of TB meningitis/CNS TB?
All patient with military TB should have a lumbar puncture to exclude TB meningitis
The symptoms can be varied. Initially can be subtle with just personality change and headache, then becomes meningitic and finally comatose over several weeks.
It is usually more insidious onset than viral/bacterial meningitis.
MRI will show leptomeningeal enhancement
LP will show high protein, low glucose, and lymphocytosis
If a patient has TB meningitis then the paradoxical reaction to ATT can be fatal. They are therefore given steroids when starting treatment. The treatment is also longer (12 months).
what are the features of pericardial TB?
Pericardial TB can result in a pericardial effusion and in tamponade. Signs include pericardial rub or kussmaul’s sign.
Paradoxical reaction can result in tamponade.
Duration of treatment is 6 months. Steroids are given at the start of treatment
what is are the features of disseminated/miliary TB?
Miliary TB has a characteristic appearance on CXR/CT. It is widespread throughout the patient and is often found in multiple sites including CNS/bone marrow/pericardium.
All patients with miliary TB should have neuroimaging (CT/MRI head) +/- lumbar puncture to exclude CNS involvement.
Treatment for military TB shouldn’t be delayed whilst awaiting biopsies
ATT is usually started as soon as it is determined whether or not there is CNS
involvement
