Session 6 Flashcards
Describe the age distribution of TB infections in the UK.
Very few infections in the very young or very old, peak in middle aged people in late 20s/early 30s.
What causes TB?
Bactria belonging to the Mycobacterium tuberculosis complex: 7 species such as M. tuberculosis, M. bovis, M. africanum.
Describe the properties of Mycobacterium tuberculosis.
Non-motile; rod-shaped; obligate aerobe; mycolic acids, complex waxes and glycolipids make cell wall very thick, rigid and resistant to staining; slow-growing.
What staining is done when looking for TB causative organisms?
Acid alcohol fast staining as gram staining is ineffective because of the bacterias thick cell wall.
How is TB spread?
Via droplets produced in sneezing, coughing, etc.
How long must someone typically be exposed to TB before they will acquire it?
Prolonged exposure of typically 8 hours/a day to 6 months.
Describe the pathogenesis of a primary TB infection.
Pathogen is inhaled and engulfed by alveolar macrophages; can multiply within macrophages and resist destruction; macrophages move to local lymph nodes; primary complex is formed of Ghon’s focus and a draining lymph node and the TB infection begins.
How may latent TB develop?
If a primary TB infection is contained in the lungs it may remain there inactively and cause post-primary TB if the bacteria overcome the body’s immune defences later on.
Describe the features of latent TB on examination.
Bacterial contained so CXR usually normal, negative sputum cultures, no symptoms, not infectious, TST or IFN gamma test results are usually positive.
Describe the main features of TB disease on examination.
Abnormal CXR, positive sputum cultures, cough, fever, weight loss, often infectious, positive TST or blood tests.
What are the risk factors of reactivation of TB?
HIV, substance abuse, long-term corticosteroid use, immunosuppressive therapy, TNF-alpha antagonists, organ transplant, haematological malignancy, kidney disease/dialysis, DM, silicosis, low weight.
What is a caseating granulomata?
A mass of dead/dying inflammatory cells in the lung parenchyma or mediastinal lymph nodes, usually due to TB infection.
Where is extrapulmonary TB likely to affect?
Larynx, lymph nodes, pleura, brain, kidneys, bones, joints.
In whom is extrapulmonary TB typically found?
Hiv-infected/immunocompromised people, young children.
What is miliary TB?
Rare and severe TB infection where the infection is carried to all parts of the body via the bloodstream.
What are the risk factors in contracting TB?
Travel history (mainly south Asia and sub-saharan Africa), HIV, immunocompromisation, homeless, drug users, prisoners, people in close contact with sufferers, young adults.
What causes the symptoms of TB?
Macrophages releasing cytokines.
How is TB investigated?
CXR, sputum early morning samples, induced sputum, bronchoscopy.
What laboratory tests are performed in ?TB?
Sputum smears, Ziehl Nielsen/auramine staining, gastric aspirates in children, cultures (gold standard).
What is TST testing?
Tuberculin sensitivity testing to assess immune response in order to test for latent TB.
What are IGRAs in TB testing?
Interferon gamma releasing assays used to detect TB infection, but cannot distinguish between latent and active TB infections.
What drugs are given to treat TB?
First line: rifampicin, isoniazid, pyrazinamide, ethambutol. Second line: quinolones, ethionamide, cycloserine, etc.
How is TB treated?
Combination therapy with anti TB drugs and vit D, close monitoring and compliance. May consider surgery
Why is combination therapy used in TB?
The causative bacteria are quick to mutate and can confer increased resistance so the infection is more difficult to treat.
How is TB treatment adherence ensured?
Via directly observed therapy or video observed therapy so it is ensured that patients are definitely taking medications properly.
What is MDR TB resistant to?
Rifampicin and isoniazid.
What is XDR YB resistant to?
Fluoroquinolones and at least one injectable.
How is resistant TB treated?
4/5 drug regime over a longer duration using quinolones, aminoglycosides, PAS, cycloserine, ethionamide, etc.
How is TB prevented?
Disease is notifiable by law to Public Health England to monitor spread and trigger tracing procedures; PPI and negative pressure isolation used in treatment; susceptibility of sufferer’s contacts is reduced via addressing risk factors and vaccination; BCG given to at risk groups.
Define asthma.
Chronic inflammatory disorder of the airways resulting in reversible airway obstruction, inflammation, bronchoconstriction and increased mucus production.
Describe the pathogenesis of asthma.
Allergen binding to IgE on mast cells causes activation of the Th-1 and Th-2 responses via IL-12, this causes cytokine release which produces the symptoms of asthma (type 1 hypersensitivity reaction).
What do repeated asthma attacks lead to/
Remodelling causing damaged epithelium which leads to increased smooth muscle thickness.
What is the effect of asthma on the FEV1.0/FVC ratio?
Decreases it as air takes longer to enter the lungs due to the obstructive pathology.
How does asthma usually present?
Tight chested, persistent cough (often worse at night, exercise-induced or dry), attacks where can’t breathe, wheeze, breathlessness.
Define a respiratory wheeze.
High pitched, expiratory musical sound due to narrowed airways.
Define stridor.
High pitched, inspiratory musical sound.
What is useful in taking a history for asthma?
Full symptom history, PMH for other allergies, family history, social history for allergens, drug history for exacerbating medications (ACE-I, beta-blockers).
How is asthma managed?
Educate patients on how to use inhalers, prevent exacerbations by reducing allergens
How is asthma treated initially?
Give bronchodilators for a moth then review to see if improvement, if improved then continue to treat as asthma.
What treatment options can be given for more severe asthma?
Short acting beta agonist inhalers, steroid inhalers, long acting beta agonist inhalers, steroid tablets.
What treatment should be given for a severe asthma attack?
Salbutamol nebs and oxygen or IV salbutamol if very severe, if life-threatening then consider intubation and ITU.
