Allergic disorder (RESP) Flashcards
Define allergic disorder.
Conditions caused by hypersensitivity of the immune system to typically harmless substances
Describe the pathophysiology of allergic disorder.
IgE binds to receptor on mast cell or basophil, causing degranulation and release of histamine
What are some causes/triggers of allergic disorder? (10)
- dust (mites)
- foods
- latex
- medications
- insect stings
- mold spores
- pet dander
- pollen
- genetics
- stress
What is type I hypersensitivity (allergic disorder)?
Antigen reacts with IgE bound to mast cells –> allergic reaction
What conditions can type I hypersensitivity cause (allergic disorder)?
- anaphylaxis
- atopy e.g. asthma, eczema, allergic rhinitis
- (triggers: drugs, penicillin, bee/wasp stings, peanuts)
What is type II hypersensitivity (allergic disorder)?
Antibody mediated: IgG or IgM binds to antigen on cell surface
What conditions can type II hypersensitivity cause (allergic disorder)? (9)
- autoimmune haemolytic anaemia
- acute haemolytic transfusion reactions
- haemolytic disease of newborns (mismatched RhD alleles)
- immune thrombocytopenia (platelet surface proteins)
- Goodpasture’s syndrome
- Graves disease (TSH antibodies bind to thyrotropin receptor)
- rheumatic fever
- pernicious anaemia
- pemphigus vulgaris/bullous pemphigoid
What is type III hypersensitivity (allergic disorder)?
Free antigen and antibody (IgG, IgA) combine –> immune complex
What conditions can type III hypersensitivity cause (allergic disorder)? (8)
- serum sickness
- SLE
- post-Streptococcal glomerulonephritis
- vasculitis
- arthritis (e.g. RA)
- extrinsic allergic alveolitis (especially acute phase)
- hepatitis
- MS
What is type IV hypersensitivity (allergic disorder)?
T-cell mediated - sensitised Th cells –> delayed reaction
What conditions can type IV hypersensitivity cause (allergic disorder)? (7)
- TB
- GvHD
- allergic contact dermatitis
- scabies
- extrinsic allergic alveolitis
- MS
- Guillain-Barre syndrome
What can trigger type IV hypersensitivity (allergic disorder)?
Nickel salts and hair dyes
What are the clinical features of allergic disorder? (4)
- runny nose & sneezing
- redness & itching of eyes
- coughing & wheezing
- rashes & hives (urticaria)
What investigations are done for allergic disorder? (4)
- skin prick testing - most commonly used, easy to perform and inexpensive - done for type I hypersensitivity reactions (IgE-mediated) that cause systemic reaction
- scratch testing - done for contact dermatitis and for skin reactions (type IV hypersensitivity, not IgE-mediated)
- bloods - measure concentrations of specific IgE antibodies
- serum tryptase - specific marker of mast cell activation
Describe the management plan for allergic disorder. (4)
- antihistamines e.g. cetirizine
- glucocorticoids
- emergency - adrenaline auto-injectors for self-treatment (epi-pen)
- allergen immunotherapy
What are some specific examples of allergic disorder? (3)
- hypersensitivity pneumonitis
- allergic bronchopulmonary aspergillosis
- allergic rhinitis
Describe the aetiology of hypersensitivity pneumonitis (allergic disorder). (3)
- type III hypersensitivity –> immune-complex mediated
- type IV also plays a role
- causes inflammation of alveoli and distal bronchioles
What are the causes of hypersensitivity pneumonitis (allergic disorder)? (5)
- bird fancier’s lung: avian proteins from bird droppings
- farmer’s lung: spores of Saccharopolyspora rectivirgula from wet hay
- malt worker’s lung: Aspergillus clavatus
- mushroom worker’s lung: thermophilic actinomycetes
- occupation exposure to organic dust (including Actinomycetes bacteria, animal proteins or reactive chemicals)
How does hypersensitivity pneumonitis (allergic disorder) present? (2)
- acute: 4-8h after exposure, dyspnoea, cough, fever
- chronic: weeks-months after exposure, dyspnoea, lethargy, productive cough, anorexia, weight loss, bibasilar rales
What investigations are done for hypersensitivity pneumonitis (allergic disorder)? (7)
- serologic assays for specific IgG antibodies
- FBC: no eosinophilia, leukocytosis, anaemia
- ESR: high
- albumin: low
- CXR/CT: upper/mid-zone fibrosis, centrilobular ground glass nodules
- diffusing lung capacity of CO: decreased
- bronchoalveolar lavage: lymphocytosis
How do we manage hypersensitivity pneumonitis (allergic disorder)? (2)
- avoid precipitating factors
- oral glucocorticoids (prednisolone)
What is the aetiology of allergic bronchopulmonary aspergillosis (allergic disorder)?
- colonisation of airways by Aspergillus fumigatus –> IgE and IgG-mediated immune responses
- usually in asthmatic and CF patients
- release of proteolytic enzymes, mycotoxins, antibodies –> airway damage:
- initially causes bronchoconstriction
- persistent inflammation –> permanent damage –> bronchiectasis
How does allergic bronchopulmonary aspergillosis (allergic disorder) present? (3)
- difficult to control asthma
- recurrent episodes of pneumonia with wheeze, cough, sputum, dyspnoea, fever, malaise
- bronchiectasis
What investigations are done for allergic bronchopulmonary aspergillosis (allergic disorder)?
- immediate skin test reactivity to Aspergillus antigens
- Aspergillus-specific IgE radioallergosorbent test - RAST
- bloods: eosinophilia, raised total serum IgE, raised specific IgE and IgG to A. fumigatus
- Aspergillus in sputum
- CXR
- CT - lung infiltrates, central bronchiectasis
- PFTs - reversible airflow limitation, reduced lung volumes/gas transfer
What does CXR show in allergic bronchopulmonary aspergillosis (allergic disorder)? (4+2)
- transient patchy shadows
- segmental collapse or consolidation
- distended mucous-filled bronchi
- signs of complications:
- fibrosis in upper lobes
- bronchiectasis
How do we manage allergic bronchopulmonary aspergillosis (allergic disorder)? (2)
- oral corticosteroids (acute)
- azole antifungal (itraconazole)
Describe the aetiology of allergic rhinitis (allergic disorder).
- common URT condition
- characterised by: nasal pruritus, sneezing, rhinorrhoea, nasal congestion
- associated symptoms:
- palate, throat, ear and eye itching
- eye redness, puffiness, water discharge
- mediated by IgE-associated response to ubiquitous indoor and/or outdoor environmental allergens
- sometimes due to occupational/hobby exposures to proteins that do not commonly provoke IgE-mediated responses
- e.g. woodworkers becoming sensitised to wood dusts, or food service workers becoming sensitised to grain dusts
How does allergic rhinitis (allergic disorder) present? (7)
- nasal pruritus
- sneezing
- rhinorrhoea
- nasal congestion
- palate, throat, ear and eye itching
- eye redness, puffiness and watery discharge
- fatigue and irritability
What are some risk factors for allergic rhinitis (allergic disorder)? (4)
- Fx of atopy
- age <20
- Western lifestyle
- inadequate exposure to animals and other microorganism-rich environments in early life
What investigations are done for allergic rhinitis (allergic disorder)? (4)
- trial of antihistamine or intranasal corticosteroids
- Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ) and Rhinitis Control Assessment Test (RCAT)
- allergen skin-prick testing
- in-vitro specific IgE determination
How do we manage allergic rhinitis (allergic disorder)? (6)
- oral/intranasal antihistamine (cetirizine) + allergen avoidance
- oral/intranasal decongestant (oxymetazoline)
- nasal saline *irrigation**
- sublingual immunotherapy (SLIT)/subcutaneous immunotherapy (SCIT)
- LTRA
- intranasal iprotropium
