Respiratory p2 Flashcards
Where does tuberculosis infection tend to affect?
lung, lymph nodes and gut
What is Primary TB?
syndrome produced by M.Tuberculosis in those not previously affected
Describe the onset/location of primary tb
common sites: sub-pleural in the mid-zones of the lungs, in the pharynx or terminal ileum
mild inflammatory response at the site of infection followed by spread to regional lymph nodes
infection then spreads to hilarity, cervical or mesenteric nodes respectively
What is the primary complex?
infective focus + lymph node involvement
What is the ghon focus?
the infective focus in the lung
What happens 1-2 weeks after infection with M.Tuberculosis ?
Onset of immune sensitivity - tissue reaction at both sites of the primary complex changes to form caseating granuloma
In the majority of cases, these heal with fibrosis, and frequently calcify without therapy
What is the presentation of the patient at caseating granuloma stage?
asymptomatic or have a single enlarged LN that may be palpable if cervical
Viable bacteria may remain within walled off in the primary complex, giving latent TB
Describe the methods by which primary TB can become symptomatic
Ghon focus erodes through the visceral pleura to discharge organisms and cause TB pleurisy / pleural effusion
Enlarged hilar LNs can cause bronchial obstruction and collapse
The hilar lymph nodes can erode into bronchus and rupture (bronchopneumonia)
The enlarging nodes can erode into vessels, giving miliary dissemination to the lung or systemic dissemination (pulmonary vein)
What is post-primary (secondary) TB?
M.Tuberculosis re-infection in tuberculin-sensitive individuals
How does secondary tb occur?
infection can be from exogenous sources, or more commonly ‘reactivation’ from a healed primary complex
Immediate granulomatous response to the disease, thus regional lymph involvement is not common
in the lung, this creates a classical apical lesion termed an Assman focus, with destruction of lung parenchyma leading to cavitation
What are the outcomes of secondary TB?
Lesion may heal with fibrosis and calcification if the immune system is strong, or will progressively enlarge in those with poor immune systems
This has greater risks of eroding into vessels/airways and causing complications
What are the symptoms of TB?
non-specific: malaise, night sweats, anorexia, weight loss
When do specific symptoms of TB occur?
Late, in established disease:
productive mucoid cough
repeated small haemoptysis
pleural pain
Can present with pneumonia or pleural effusion. on examination there may only be a fever and apical crepitations, with late signs of consolidation or pleural effusion
patients may be clubbed in advanced disease
How can TB be coughed out?
release of tubercle bacilli into the main bronchus
Who are the high risk patients for TB?
endemic areas previously treated for TB close contact with TB immunosuppressive co-morbidities / drug tx live in overcrowded conditions alcohol/drug users
What are the investigations of active pulmonary TB?
SPUTUM sample: 3 x (1 in morning)
Microscopy(24h) + PCR + Culture (takes 6 weeks)
sputum grows acid-fast bacilli that stain red with Zeihl-Neelsen staining. This is mycobacterium tuberculosis and the diagnosis is TB.
If sputum = negative, bronchoscopy with biopsy or broncho-alveolar lavage may be useful
CXR: upper lobe cavitation, pleural effusions, lymphadenopathy
Ix for extra pulmonary disease as clinically indicated
What are the investigations for latent TB?
Mantoux test: TB antigen injected, size of wheal reaction monitored
>5mm = +VE in immunosuppressed, prior TB or recent contacts >10mm = +ve in those with risk factors for TB >15mm = +ve in any individual
Interferon gamma release assay: IGRA blood test also required to diagnose latent TB in immunocompromised individuals (can have false -ves in skin test)
What does a positive test for latent TB lead to?
Assessment for active TB
if no evidence, treat for latent TB
FBC, U+E, LFT to rule out other causes
screening for HIV, HEP B/C
What is the management of ACTIVE TB?
Admit - negative pressure side room OR
TB service within 2 weeks. do not delay referral
Assess risk factors for drug resistant TB
RIPE: Rifampicin + isoniazid 6 months with Pyraziname and ethambutol for first 2 months
If CNS involvement, R+I continued for 12 months
If poor adherence - given under key worker supervision
What are the risk factors for MDR TB?
previous tb treatment from endemic areas contacts with MDR-TB poor adherence to current treatment aged 25-45 HIV co-infection assess with PCR
How are household members managed if positive TB?
Notifiable disease:
All household members and close contacts should be traced and assessed for latent TB
Casual contact (work) should be traced only if the person with TB is particularly infectious (10% or more of close contacts develop TB) or if casual contacts are at increased risk of infection (healthcare workers/people with HIV)
What is the management of MDR-TB?
continue infection control measures until pulmonary / laryngeal disease has been excluded
treat with at least 6 drugs to which it is sensitive
What is the management of latent TB?
treat with 3 months of rifampicin and isoniazid (with pyridoxine)
What are the drug side effects of the TB treatment drugs?
Rifampicin: abnormal LFTs, pink urine (red-and-orange-pissin). Also a cytochrome P450 inducer
Isoniazid: peripheral neuropathy / encephalopathy. very rare when prophylactic pyridoxine co-prescribed (I’m-so-numb-azid)
Pyrazinamide: hepatotoxic
Ethambutol: optic neuritis, assess with colour vision testing (eye-tham-butol)
R, I and P all associated with hepatotoxicity