ALLERGIC DISEASE
 
PEDBASE.org - The Pediatric Database - Detailed information of ALLERGIC DISEASE

 

  •  

    ALLERGIC DISEASE

     

    DEFINITION:

    Allergy is a hypersensitive reaction to the presentation of an allergen due to the propensity to develop a sustained IgE response following antigenic stimulation.

    EPIDEMIOLOGY:

    • incidence: one of the most common health problems 12-20% of the population is affected
    • age of onset:
      • any
    • 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 following antigenic stimulation
    • 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")
    • MW usually between 5-60 x 1000 daltons & include proteins, glycoproteins, polysaccharides, and drugs
    • types:

    1. Pollens

    • grass, trees, weeds

    2. Fungi

    • spores, mycelial fragments

    3. Foods

    • codfish (a calcium-binding parvalbumin)
    • eggwhite protein (ovomucoid, ovalbumin, conal-bumin)
    • peanuts (storage proteins)

    4. Hymenoptera Venoms

    • vespids (hornets, yellow jackets, wasps)
    • bees (honeybees, bubblebees)
    • react with protein in the venom, i.e, enzymes

    5. Mammals

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

    6. Antropods

    • dust mites, blood worms

    3. IgE

    • IgE is a Homocytotropic Antibody: an antibody capable of interacting with target cells such that these 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 for 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

     

    CLINICAL FEATURES:

    • see files on individual diseases

    1. Allergic Rhinitis

  • 1. Nasal Mucosa Manifestations

    • paroxysms of sneezing, nasal congestion, clear and profuse rhinorrhea, pruritis of the nose, palate, pharynx, and middle ear

    • 2. Hives (Urticaria)

  • 1. Skin Manifestations

    • multiple, circumscribed, smooth, raised, erythematous, pruritic weals

    • 3. Atopic Dermatitis (Ezcema)

  • 1. Skin Manifestations

    • "itch that rashes"
    • first symptom is pruritis with subsequent appearance of a rash which is initially a diffuse erythematous flush which may then evolve into erythematous weeping plaques and if chronic forms dry, red, scaly plaques (lichenified) in a specific distribution based upon age of onset and triggering allergens

    •  

    4. Allergic Asthma

  • 1. Respiratory Manifestations

    • cough, wheeze, and/or dyspnea upon exposure to allergen

    • 5. Anaphylaxis

  • 1. Systemic Manifestations

    • urticaria, bronchospasm with acute airway obstruction, and circulatory collapse

    •  

    INVESTIGATIONS:

    1. In Vivo Tests

    1. Skin Tests

  • 1. Immediate
  • 2. Delayed
  • 3. Patch

    • 2. Challenges

  • 1. Conjunctival
  • 2. Oral
  • 3. Bronchial

    • 2. In Vitro Tests

    1. Immunoassays

  • 1. Radio Allergosorbent Test (RAST)

    • allergen bound to a paper solid phase
    • patients serum (with IgE) added
    • mixed with radiolabelled anti(IgG)-IgE
    • radiolabel (gamma radiation) quantified

  • 2. Enzyme Linked Immunosorbent Assay (ELISA)

    • allergen bound to a plastic solid phase
    • patients serum (with IgE) added
    • mixed with enzyme-linked anti(IgG)-IgE
    • enzyme detected by conversion of a substrate to a coloured or fluorescent product

  • 3. (MAST)

    • allergen bound to a thread solid phase
    • patients serum (with IgE) added
    • mixed with enzyme-linked anti(IgG)-IgE
    • enzyme detected by production of light when the enzyme catalyzes substrate conversion

    •  

    MANAGEMENT:

    1. Supportive

    • may need long-term counselling if these chronic conditions are severe

     

    2. Principles of Therapy

    • see individual disorders for specific therapies

    1. Avoidance

    • of allergens

    2. Medications

    1. Prophylactic Therapy

    • intranasal/oral corticosteroids
    • sodium cromoglycate

    2. Acute Therapy

    • antihistamines
    • beta-2-agonists
    • topical corticosteroids

    INTERNET LINKS:

    HON Allergy Glossary

     

     

 

Pediatric Database - ALLERGIC DISEASE

 

Pediatric Organization - Pedbase [at] Gmail.com

 
1994 -2007 Pedbase.org 

Powered by Database of Pediatrics- ALLERGIC DISEASE