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ASTHMA - ALLERGIC

DEFINITION:

An inflammatory disorder of the respiratory mucosa initiated by an IgE-mediated hypersensitivity.

EPIDEMIOLOGY:

incidence: ?
age of onset:
- usually greater than 4 years of age
risk factors:
- family history of atopy
associations:
- an allergic triad
  - 50-80% of patients with atopic dermatitis will go on to develop asthma and/or allergic rhinitis

PATHOGENESIS:

1. Allergy

1. Background

allergy is the manifestation of a hypersensitive reaction to the presentation of an allergen due to the propensity of the affected individual to develop a sustained IgE response - the distinguishing feature of the allergic individual is the propensity to develop a sustained IgE response - there are several types of allergies based upon where the hypersensitive reaction occurs:

Surface-Allergy

Nasal Mucosa-Allergic Rhinitis
Skin-Hives (Urticaria), Atopic Dermatitis
Respiratory Tract-Allergic Asthma
Systemic-Anaphylaxis

2. Allergens

allergens are compounds capable of inducing human IgE antibody formation ("sensitization")

3. IgE

IgE is a Homocytotropic Antibody: an antibody capable of interacting with target cells such that there cells release mediators on contact with specific antigens
the IgE receptor consists of an externally located alpha chain that binds the IgE and is noncovalently associated with a beta chain and two gamma chains
there are two categories of IgE receptors dependent upon the type of cells targetted and the type of mediators re-leased from these cells:

1. Type 1

target cells - mast cells, basophils
affinity - high affinity fro IgE
mediators - histamine, ECF-A, leukotrienes, bradykinins, prostaglandins, PAF, anaphylatoxins

2. Type 2

target cells - lymphocytes, platelets, eosino-phils, monocytes-macrophages
affinity - low affinity for IgE
mediators - chemotaxic factors, IgE binding factors (T cells), mitogens (B cells), inflammatory mediators

2. Allergic Asthma

1. Background

an allergy specific to the respiratory mucosa in suscep-tibe individuals

2. Allergens

1. Pollens

grass (freshly-cut), trees, weeds

2. Fungi

spores, mycelial fragments

3. Mammals

cats, dogs, rodents, horses
react with the saliva and urine

4. Antropods

dust mite feces, blood worms

5. Foods

seafood, shellfish, peanuts, kiwi, diary products

6. Others

feathers

3. IgE

within the respiratory mucosa Type 1 and Type 2 homocyto-tropic antibody responses occur

CLINICAL FEATURES:

1. Respiratory Manifestations

1. When the appropriate allergen is encountered:

cough
wheeze
dyspnea
associated symptoms
- allergic rhinitis - runny nose
- atopic dermatitis - dry skin

2. Timing

1. Seasonal

symptoms wax and wane with the seasons
pollens most likely allergen

2. Perennial

symptoms occur year round
fungi, mammals, antropods most likely allergens

3. Intermittent

occasional episodes with no symptoms in between

INVESTIGATIONS:

1. Serum

elevated IgE
eosinophilia

2. Allergy Tests

In Vivo - skin tests - immediate, delayed, patch skin test
In Vitro - Immunoassays -RAST, MAST, ELISA

MANAGEMENT:

I. APPROACH

1. Diagnosis + Education

2. Goals of Therapy

3. Avoidance of Allergen

4. Medications

1. Beta-2 Agonists

2. Non-Steroidal Antiinflammatory Drugs

Intal
Ketotifen
Tilade

3. Steroids

Inhaled
Oral

1. Diagnosis + Education

1. What is Asthma

diagnosis based upon history, physical, investigations, etc
2 components - inflammation, bronchospasm

2. Identification of Allergens

which allergens trigger the asthma

3. Management Plans For:

interval asthma - period between exacerbations
acute exacerbation
when asthma is out of control
also remember that controlling allergic rhinitis (+/-sinusitis) will help to control the allergic asthma

2. Goals of Therapy

absence of symptoms upon exposure to allergen
normal exercise tolerance
normal spirometry and peak flows
infrequent or no bronchodilator use

3. Avoidance of Allergens

1. Pollens and Molds

shut windows and use window air conditioners during warm days or days when the pollen count is high
dehumidification of home
clean with Clorox (1-10% solution - 1 tbs in a pail of water with detergent [Tide])

2. Mammals

weekly baths of pets
remove pets from house or getting rid of pet is the best method of reducing the level of animal dander

3. Antropods (Dust Mites)

1. Vacuum and Dust Effectively

central vacuum most effective
upright vacuum least effective
damp mop or dust all hard surfaces - floors, furniture
vacuum mattress and pillow at least once per week

2. Maintain Optimal Humidity

keep indoor humidity about 50% in the summer and 35% in the winter
use an air conditioner in the summers
can moniter humidity with a hygrometer

3. Bedroom

1. Mattress

use a water bed or cover mattress with a dust mite impermeable barrier
encase and vacuum box springs
wash mattress protectors weekly in hot water

2. Pillow

avoid feather or foam pillows
use pillows of synthetic fibre

3. Sheets

wash bedding and curtains weekly
- temperature must be > 130 degrees F to kill mites
- may use 4 oz. of Australian tea tree oil as well (sold in health food stores)

4. Blankets

unnapped, washable, synthetic or cotten
avoid wool blankets or duvets

5. Furnishings

remove all rugs, carpeting, drapes, dust ruffles
frequently clean bedroom
avoid or store dust-collecting toys outside bedroom
keep bedroom door shut

4. Medications

1. Acute

in anticipation of encountering a known allergen, take Intal 1 nebule or 4 puffs qid one day prior to exposure

2. Chronic

see Management of "Asthma - Chronic"

Pediatric Database - ASTHMA - ALLERGIC

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