Allergic disorder (RESP)

Question 1

Define allergic disorder.

Answer 1

Conditions caused by hypersensitivity of the immune system to typically harmless substances

Question 2

Describe the pathophysiology of allergic disorder.

Answer 2

IgE binds to receptor on mast cell or basophil, causing degranulation and release of histamine

Question 3

What are some causes/triggers of allergic disorder? (10)

Answer 3

• dust (mites)
• foods
• latex
• medications
• insect stings
• mold spores
• pet dander
• pollen
• genetics
• stress

Question 4

What is type I hypersensitivity (allergic disorder)?

Answer 4

Antigen reacts with IgE bound to mast cells –> allergic reaction

Question 5

What conditions can type I hypersensitivity cause (allergic disorder)?

Answer 5

• anaphylaxis
• atopy e.g. asthma, eczema, allergic rhinitis
• (triggers: drugs, penicillin, bee/wasp stings, peanuts)

Question 6

What is type II hypersensitivity (allergic disorder)?

Answer 6

Antibody mediated: IgG or IgM binds to antigen on cell surface

Question 7

What conditions can type II hypersensitivity cause (allergic disorder)? (9)

Answer 7

• 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

Question 8

What is type III hypersensitivity (allergic disorder)?

Answer 8

Free antigen and antibody (IgG, IgA) combine –> immune complex

Question 9

What conditions can type III hypersensitivity cause (allergic disorder)? (8)

Answer 9

• serum sickness
• SLE
• post-Streptococcal glomerulonephritis
• vasculitis
• arthritis (e.g. RA)
• extrinsic allergic alveolitis (especially acute phase)
• hepatitis
• MS

Question 10

What is type IV hypersensitivity (allergic disorder)?

Answer 10

T-cell mediated - sensitised Th cells –> delayed reaction

Question 11

What conditions can type IV hypersensitivity cause (allergic disorder)? (7)

Answer 11

• TB
• GvHD
• allergic contact dermatitis
• scabies
• extrinsic allergic alveolitis
• MS
• Guillain-Barre syndrome

Question 12

What can trigger type IV hypersensitivity (allergic disorder)?

Answer 12

Nickel salts and hair dyes

Question 13

What are the clinical features of allergic disorder? (4)

Answer 13

• runny nose & sneezing
• redness & itching of eyes
• coughing & wheezing
• rashes & hives (urticaria)

Question 14

What investigations are done for allergic disorder? (4)

Answer 14

• 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

Question 15

Describe the management plan for allergic disorder. (4)

Answer 15

• antihistamines e.g. cetirizine
• glucocorticoids
• emergency - adrenaline auto-injectors for self-treatment (epi-pen)
• allergen immunotherapy

Question 16

What are some specific examples of allergic disorder? (3)

Answer 16

• hypersensitivity pneumonitis
• allergic bronchopulmonary aspergillosis
• allergic rhinitis

Question 17

Describe the aetiology of hypersensitivity pneumonitis (allergic disorder). (3)

Answer 17

• type III hypersensitivity –> immune-complex mediated
• type IV also plays a role
• causes inflammation of alveoli and distal bronchioles

Question 18

What are the causes of hypersensitivity pneumonitis (allergic disorder)? (5)

Answer 18

• 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)

Question 19

How does hypersensitivity pneumonitis (allergic disorder) present? (2)

Answer 19

• acute: 4-8h after exposure, dyspnoea, cough, fever
• chronic: weeks-months after exposure, dyspnoea, lethargy, productive cough, anorexia, weight loss, bibasilar rales

Question 20

What investigations are done for hypersensitivity pneumonitis (allergic disorder)? (7)

Answer 20

• 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

Question 21

How do we manage hypersensitivity pneumonitis (allergic disorder)? (2)

Answer 21

• avoid precipitating factors
• oral glucocorticoids (prednisolone)

Question 22

What is the aetiology of allergic bronchopulmonary aspergillosis (allergic disorder)?

Answer 22

• 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

Question 23

How does allergic bronchopulmonary aspergillosis (allergic disorder) present? (3)

Answer 23

• difficult to control asthma
• recurrent episodes of pneumonia with wheeze, cough, sputum, dyspnoea, fever, malaise
• bronchiectasis

Question 24

What investigations are done for allergic bronchopulmonary aspergillosis (allergic disorder)?

Answer 24

• 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

Question 25

What does CXR show in allergic bronchopulmonary aspergillosis (allergic disorder)? (4+2)

Answer 25

- transient patchy shadows - segmental collapse or consolidation - distended mucous-filled bronchi - signs of complications: - fibrosis in upper lobes - bronchiectasis

Question 26

How do we manage allergic bronchopulmonary aspergillosis (allergic disorder)? (2)

Answer 26

- oral corticosteroids (acute) - azole antifungal (itraconazole)

Question 27

Describe the aetiology of allergic rhinitis (allergic disorder).

Answer 27

- 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

Question 28

How does allergic rhinitis (allergic disorder) present? (7)

Answer 28

- nasal pruritus - sneezing - rhinorrhoea - nasal congestion - palate, throat, ear and eye itching - eye redness, puffiness and watery discharge - fatigue and irritability

Question 29

What are some risk factors for allergic rhinitis (allergic disorder)? (4)

Answer 29

- Fx of atopy - age <20 - Western lifestyle - inadequate exposure to animals and other microorganism-rich environments in early life

Question 30

What investigations are done for allergic rhinitis (allergic disorder)? (4)

Answer 30

- 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

Question 31

How do we manage allergic rhinitis (allergic disorder)? (6)

Answer 31

- oral/intranasal antihistamine (**cetirizine**) + allergen avoidance - oral/intranasal decongestant (**oxymetazoline**) - nasal saline **irrigation** - sublingual immunotherapy (SLIT)/subcutaneous immunotherapy (SCIT) - **LTRA** - intranasal iprotropium