Tuberculosis Flashcards
What is a Ghon complex?
Ghon focus (caseating granuloma) + hilar node
Visible as small calcified nodule on the lung
Outline the pathology of TB.
- Inhalation (initial infection)
- Innate immune phase - TB bacilli cleared before reaching lymph nodes (no memory of infection) OR are ingested by macrophages but survive, alveolar walls damaged by cytokines & inflammation
- Adaptive immune phase - containment of infection in 90% of individuals (either via calcified granuloma formation or elimination by T cells), remaining patients form caseating granulomas containing bacilli (Ghon focus)
- Primary or latent TB
What is the difference between primary & latent TB?
Primary TB: (4-6 weeks after initial infection)
Inability to control bacilli leads to pulmonary TB
-> Primary complex/small pleural effusion
-> Post-primary immunity heals/calcifies lungs (but tuberculin test is +ve)
(Reactivation/re-infection can cause adult post-primary pulmonary TB)
Latent TB:
Initial containment of infection with granuloma which when ruptured (months-years later) disseminates the bacilli around the body
Causes pulmonary and extrapulmonary TB
Pulmonary: (6-12 months)
- Collapse & bronchiectasis
- Pleural effusion
- Pneumonia
Extrapulmonary: (within 3yrs)
Small no. of bacilli:
- Bones, joints, lymph nodes, kidney, GI
Large no. of bacilli:
- Miliary TB (lesions in infected organs appear as millet seeds on X-ray)
- TB meningitis
What are some of the factors implicated in the reactivation of TB?
Ageing Malnutrition HIV co-infection Immunosuppressants e.g. corticosteroids, chemotherapy Diabetes Chronic kidney disease
What are the signs and symptoms of pulmonary TB? What can be seen on the chest X-ray?
- productive cough +/- haemoptysis
- weight loss, fever, night sweats
- laryngeal involvement -> hoarse voice + cough
- pleura -> pleuritic pain
CXR: consolidation +/- cavitation OR pleural effusion OR thickening/widening of mediastinum (caused by hilar/paratracheal lymphadenopathy)
What are some of the signs and symptoms of extrapulmonary TB?
LYMPH NODE: (extrathoracic more commonly than intrathoracic/mediastinal)
Firm, non-tender enlargement of a cervical or supraclavicular node -> necrotic centre (visible on CT) which becomes purulent if peripheral
Overlying skin frequently indurated +/-purulent discharge
ORTHOPAEDIC: spinal most common
Osteomyelitis -> destruction of bone/cartilage due to eroding granulomas (& new bone not formed) -> pain/swelling of joint causing limited range of movement
MRI (differentiates abscesses from granulomas) shows: soft tissue swelling, osteopenia, narrowed joint spaces, subchondral erosions on both sides of joint
MENINGITIS: lesions in CNS which rupture to release TB bacilli
Gelatinous exudate in meninges -> same CNS symptoms as bacterial/viral meningitis
Detect on CT/MRI
Define and contrast consolidation and cavitation.
CONSOLIDATION = fluid in alveoli
CAVITATION = formation of cavities in lung
How is TB diagnosed?
Microbial:
- Ziehl-Neelsen/auramine-rhodamine stain (fluorescent microscopy - more sensitive)
- liquid/broth culture + anti-mycobacterials (determine drug resistance)
- PCR (identify drug-resistant strains & differentiate TB mycobacteria from non-TB mycobacteria)
CXR:
- cavitation
- miliary shadowing
- pleural effusion
- mediastinal lymphadenopathy
- collapse
- consolidation
What is the management of TB?
Rifampicin + Isoniazid + Ethambutol + Pyrazinamide
?steroids
note: rifampicin can cause urine to turn red/orange AND reduces the effectiveness of the combined contraceptive pill
Why is directly observed therapy sometimes necessary in the management of TB?
Used to achieve a good treatment completion rate (therefore lowering the global incidence of TB)
Treatment supervised by healthcare professional/family member (observed swallowing medicine)
Homeless population
What are some of the mechanisms of TB resistance?
Cell wall mutations (reduced permeability to drugs)
Enzymes modifying/altering drugs
Drug efflux
What is the formation of the BCG vaccine? What is the Mantoux test?
Bacillus Calmette-Guerin - live attenuated vaccine from Mycobacterium bovis given when Mantoux test is negative
note: no immune reaction to tuberculin but NOT immune to TB
Administered as intradermal injection into deltoid
note: accidental subcutaneous injection causes infection & suppuration
+ve Mantoux test causes severe local inflammation + scarring (area of induration > 10mm)
What are some high risk groups for TB in the UK? Who should be screened for TB?
- originated from high incidence country
- frequent travel to high incidence countries
- homelessness/overcrowding e.g. prisoners
- drug/alcohol abuse
- immune deficiency: HIV, corticosteroids/immunosuppressants, chemotherapy, nutritional deficiency, diabetes, chronic kidney disease, malnourishment
Individuals screened: healthcare workers, close contact to TB patients, homeless people, people with drug/alcohol problems, prisoners, immigrants from high incidence countries
Notifiable disease (suspected & confirmed diseases must be reported within 3 working days)
What are some important things to consider with TB & HIV co-infection?
Latent TB more likely to reactivate due to reduced CD4+ count by HIV, so disease course is accelerated
Rifampicin interacts with PIs & NNRTIs to reduce the efficacy of antiretrovirals
HAART can cause immune reconstitution inflammatory syndrome = development of new manifestations of TB/worsening of existing symptoms of TB (intensified inflammatory reaction to TB - paradoxical reaction)
Acquired rifampicin resistance
What is the blood test for TB?
Quantiferon test
Some Mycobacterium tuberculosis antigens stimulate host production of interferon-gamma
note: not applicable with BCG/atypical causative organisms
Obtain lymphocytes and culture with these antigens
+ve test results = T-lymphocytes produce interferon-gamma
(patient has been exposed to TB)
