a.. Pediatric Database (PEDBASE)
b.. Discipline: RES
c.. Last Updated: 3/10/94
ASTHMA - ALLERGIC
DEFINITION:
An inflammatory disorder of the respiratory mucosa initiated by an IgE-mediated
hypersensitivity.
EPIDEMIOLOGY:
a.. incidence: ?
b.. age of onset:
a.. usually greater than 4 years of age
c.. risk factors:
a.. family history of atopy
d.. associations:
a.. an allergic triad
a.. 50-80% of patients with atopic dermatitis will go on to develop asthma
and/or allergic rhinitis
PATHOGENESIS:
1. Allergy
a.. 1. Background
a.. 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
a.. Nasal Mucosa-Allergic Rhinitis
b.. Skin-Hives (Urticaria), Atopic Dermatitis
c.. Respiratory Tract-Allergic Asthma
d.. Systemic-Anaphylaxis
a.. 2. Allergens
a.. allergens are compounds capable of inducing human IgE antibody formation
("sensitization")
b.. 3. IgE
a.. IgE is a Homocytotropic Antibody: an antibody capable of interacting with
target cells such that there cells release mediators on contact with specific antigens
b.. 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
c.. 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
a.. target cells - mast cells, basophils
b.. affinity - high affinity fro IgE
c.. mediators - histamine, ECF-A, leukotrienes, bradykinins,
prostaglandins, PAF, anaphylatoxins
2. Type 2
a.. target cells - lymphocytes, platelets, eosino-phils,
monocytes-macrophages
b.. affinity - low affinity for IgE
c.. mediators - chemotaxic factors, IgE binding factors (T cells),
mitogens (B cells), inflammatory mediators
2. Allergic Asthma
a.. 1. Background
a.. an allergy specific to the respiratory mucosa in suscep-tibe individuals
b.. 2. Allergens
a.. 1. Pollens
a.. grass (freshly-cut), trees, weeds
b.. 2. Fungi
a.. spores, mycelial fragments
c.. 3. Mammals
a.. cats, dogs, rodents, horses
b.. react with the saliva and urine
d.. 4. Antropods
a.. dust mite feces, blood worms
e.. 5. Foods
a.. seafood, shellfish, peanuts, kiwi, diary products
f.. 6. Others
a.. feathers
c.. 3. IgE
a.. 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:
a.. cough
b.. wheeze
c.. dyspnea
d.. associated symptoms
a.. allergic rhinitis - runny nose
b.. atopic dermatitis - dry skin
2. Timing
a.. 1. Seasonal
a.. symptoms wax and wane with the seasons
b.. pollens most likely allergen
b.. 2. Perennial
a.. symptoms occur year round
b.. fungi, mammals, antropods most likely allergens
c.. 3. Intermittent
a.. occasional episodes with no symptoms in between
INVESTIGATIONS:
1. Serum
a.. elevated IgE
b.. eosinophilia
2. Allergy Tests
a.. In Vivo - skin tests - immediate, delayed, patch skin test
b.. In Vitro - Immunoassays -RAST, MAST, ELISA
MANAGEMENT:
a.. I. APPROACH
a.. 1. Diagnosis + Education
b.. 2. Goals of Therapy
c.. 3. Avoidance of Allergen
d.. 4. Medications
a.. 1. Beta-2 Agonists
b.. 2. Non-Steroidal Antiinflammatory Drugs
a.. Intal
b.. Ketotifen
c.. Tilade
c.. 3. Steroids
a.. Inhaled
b.. Oral
1. Diagnosis + Education
a.. 1. What is Asthma
a.. diagnosis based upon history, physical, investigations, etc
b.. 2 components - inflammation, bronchospasm
b.. 2. Identification of Allergens
a.. which allergens trigger the asthma
c.. 3. Management Plans For:
a.. interval asthma - period between exacerbations
b.. acute exacerbation
c.. when asthma is out of control
d.. also remember that controlling allergic rhinitis (+/-sinusitis) will help to
control the allergic asthma
2. Goals of Therapy
a.. absence of symptoms upon exposure to allergen
b.. normal exercise tolerance
c.. normal spirometry and peak flows
d.. infrequent or no bronchodilator use
3. Avoidance of Allergens
a.. 1. Pollens and Molds
a.. shut windows and use window air conditioners during warm days or days when
the pollen count is high
b.. dehumidification of home
c.. clean with Clorox (1-10% solution - 1 tbs in a pail of water with detergent
[Tide])
b.. 2. Mammals
a.. weekly baths of pets
b.. remove pets from house or getting rid of pet is the best method of reducing
the level of animal dander
c.. 3. Antropods (Dust Mites)
a.. 1. Vacuum and Dust Effectively
a.. central vacuum most effective
b.. upright vacuum least effective
c.. damp mop or dust all hard surfaces - floors, furniture
d.. vacuum mattress and pillow at least once per week
b.. 2. Maintain Optimal Humidity
a.. keep indoor humidity about 50% in the summer and 35% in the winter
b.. use an air conditioner in the summers
c.. can moniter humidity with a hygrometer
c.. 3. Bedroom
1. Mattress
a.. use a water bed or cover mattress with a dust mite impermeable barrier
b.. encase and vacuum box springs
c.. wash mattress protectors weekly in hot water
2. Pillow
a.. avoid feather or foam pillows
b.. use pillows of synthetic fibre
3. Sheets
a.. wash bedding and curtains weekly
a.. temperature must be > 130 degrees F to kill mites
b.. may use 4 oz. of Australian tea tree oil as well (sold in health
food stores)
4. Blankets
a.. unnapped, washable, synthetic or cotten
b.. avoid wool blankets or duvets
5. Furnishings
a.. remove all rugs, carpeting, drapes, dust ruffles
b.. frequently clean bedroom
c.. avoid or store dust-collecting toys outside bedroom
d.. keep bedroom door shut
4. Medications
a.. 1. Acute
a.. in anticipation of encountering a known allergen, take Intal 1 nebule or 4
puffs qid one day prior to exposure
b.. 2. Chronic
a.. see Management of "Asthma - Chronic"
