Allergy and asthma Flashcards
What is intolerance in a clinical setting?
The inability to cope with normally acceptable conditions/exposures
What is the difference between allergy and hyper-reactivity?
- hyper reactivity is an increased response to a trigger that causes a response in the normal population
- Allergy is a response to something that does not cause any reaction in the normal population
What causes wheeze/stridor in the airways in the lungs?
Increased resistance causes wheeze/stridor due to turbulence
What are the 3 components of asthma?
- Airway inflammation (eosinophil)
- Airway hyper-responsiveness
- Airway narrowing/obstruction that is reversible
What is the pathogenesis of asthma?
•Inflammatory mediators cause bronchospasm •Mediators: - IgE antibodies - IL-4, IL-33 (IL-5 and IL-13 also) - Leukotriene B4 - Tissue damaging eosinophil proteins - mast cells
What is the treatment of asthma?
- Start with a SABA: salbutamol
- Regular preventer: Inhaled corticosteroid e.g. beclamethasone
- Add on LABA: salmeterol
- Add on LTRA: leukotriene receptor antagonist e.g. montelukast
- Specialist therapies: methyxanthines or monoclonal antibodies
What is acute severe asthma?
Any one of:
•PEF 33-50%
•Respiratory rate >/25 breaths per minute
•Heart rate >/110 bpm
•Inability to complete a sentence in one breath
What investigations should be carried out in suspected asthma?
- Spirometry
- Bronchodilator reversibility
- Peak flow variability
- Bronchial hypersensitivity
What spirometry result is suggestive of asthma?
- FEV1/FVC <70%
* This is positive for obstructive disease and is not asthma specific
What bronchodilator reversibility result is suggestive of asthma?
• >/15% increase after 5mg of nebuliser salbutamol
•Increase in volume by >/200ml
What variability is suggestive of asthma in a peak flow variability test?
> 20%
What is the management of acute severe asthma?
- SABA (salbutamol) via nebuliser (oxygen driven)
- Prednisolone 40-50mg
- +/- antibiotic or a muscarinic antagonist if indicated
- If there is no improvement consider IV magnesium sulphate
What are the pathological characteristics of asthma?
- Inflammation
- Scabby epithelium
- Thickened basmenet membrane
- Thickened smooth muscle
What are the physiological characteristics of asthma
- Yellow mucous (eosinophils)
- Repair pathways
- Non elastic airways
- Increased responsiveness
- Increased sensitivity
Describe histology of the airway in a person with asthma
- Smooth muscle hypertrophy
* Mast cells
What bronchial hypersensitivity test result is indicative of asthma?
•A drop of >/20% in FEV1 by
What cytokines released by dragged epithelial cells are involved in asthma?
- TNF-a
- TGF-B
- VEGF
What do anti-IgE therapies target?
•IgE produced by mast cells
What do corticosteroids target in asthma?
- Mast cells
- Macrophages
- T helper cells
Explain allergic disease in the lung parenchyma
Type 2 immune response
•First exposure resulting in antigen presenting cell presenting antigen to T cell, forming an immune complex
•IL-12 and IFN, reactive T cells form
•On re-exposure, IgG moderates and immune complexes form
•Tissue remodelling occurs as does an immune response (neutrophils, consolidation)
What are the clinical consequences of peripheral/parenchymal disease?
- Thickening of the septae, filling of the alveolus with fluid
- Loss of O2 resulting in hypoxia and normocapnia
- Air space shadowing on the Chest x ray
What is fibrosis of the lung?
Interstitial scarring from chronic tissue remodelling/repair pathways
What is emphysema?
Interstital destruction from neutrophilic enzyme release
What are the clinical consequences of fibrosis and emphysema?
- Reduced oxygen transport into the blood stream
- Measured by carbon monoxide gas transfer during full PFTs
- Airspace shadowing on Chest X ray
What is extrinsic allergic alveolitis?
- Acute illness due to type III reaction
- Sub acute days to weeks: Type IV T cell mediated reaction
- Chronic disease - fibrosis and emphysema, the final pathway of all chronic inflammatory conditions
What is caused by allergy in the airways?
This will affect the airflow
•Increases resistance
•Causes wheeze/stridor
What is the effect of allergy in the parenchyma?
•Affects gas transfer and compliance
What is the presentation of allergic disease in the lung parenchyma acutely?
- 4-6 hours after exposure
- wheeze, cough, fever, chills, headache, myalgia, malaise, fatigue
- May last several days
- Serum sickness illness
What is the management of EAA?
- avoid trigger
- Inflammation: corticosteroids (neutrophils are moderately steroid responsive), cytotoxics
- Oxygen supplementation
