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Food Allergy

Definition
l Adverse food reaction : any abnormal reaction after the ingestion of a food
l Food intolerance : adverse physiologic response
l Food hypersensitivity (allergy) : adverse immunologic reaction
l Food aversion : mimic adverse food reactions but not reproducible when the patient
                   ingests the food in a blinded fashion

Prevalence
l children younger than 3 years : 6%
l adults in the United States : 2%
l 2.5% of newborn infants : hypersensitivity reactions to cow milk in the first year of life
l 1.5% of young children : allergic to eggs
l 0.5% of young children : allergic to peanuts

Pathogenesis
l developmental immaturity of various components of the gut barrier and immune
  system
l oral tolerance : unresponsiveness of T cells to ingested food proteins
  1. intestinal epithelial cells : nonprofessional antigen-presenting cells
  2. dendritic cells : express IL-10, IL-4, which favor generation of tolerance
  3. T regulatory cells : potent sources of TGF-beta
  4. gut flora
l traditional or class 1 food allergy : sensitization to food allergens after the ingestion
   of a food
l class 2 food allergy : after inhalation of an airborne allergen that cross-reacts with
   a specific food
l in children : cow milk, egg, peanut, soy, wheat, fish
l in adults : peanuts, tree nuts, fish, shellfish
Diagnosis
l medical history
  1. the food responsible for the reaction
  2. the quantity of the suspected food ingested
  3. the length of time between ingestion and development of symptoms
  4. whether similar symptoms occurred when the food was eaten previously
  5. whether other factors (eg, exercise) are necessary
  6. when the last reaction to the food occurred
l dietary diaries
l elimination diets
l skin prick tests
l radioallergosorbent tests
l double-blind, placebo-controlled food challenge (DBPCFC): gold standard
l open or single-blind challenges

Treatment
l strict elimination of the offending allergen : the only proved therapy
l education of patients and their families

  1. to avoid accidentally ingesting food allergens
  2. to recognizedearly symptoms of an allergic reaction
  3. to initiate early management of an anaphylactic reaction
l antihistamines : partially relieve symptoms of OAS, IgE-mediated skin symptoms but do not block systemic reactions
l oral corticosteroids
l American Academy of Pediatrics recommends
  1. "high-risk" infants be exclusively breast-fed
  2. lactating mothers avoid peanuts and nuts (to avoid sensitization through breast milk)
  3. the introduction of solid food be delayed until 6 months of age
  4. major allergens, such as peanuts, nuts, and seafood, be introduced after 3 years of age
 
Food hypersensitivity disorde
   Type    Disorders
   IgE mediated    _
   Cutaneous    Urticaria
   Angioedema
   Morbilliform rashed
   Flushing
   Gastrointestinal    Oral allergy syndrome
   Gastrointestinal anaphylaxis
   Respiratory    Acute rhinoconjunctivitis
   Bronchospasm (wheezing)
   Generalized    Anaphylactic shock
     
   Mixed IgE and cell mediated  
   Cutaneous    Atopic dermatitis
   Gastrointestinal    Allergic eosinophilic eosphagitis
   Allergic eosinophilic gastroenteritis
   Respiratory    Asthma
   
   Cell mediated    _
   Cutaneous    Contact dermatitis
   Dermatitis herpetiformis
   Gastrointestinal    Food protein-induced enterocolitis
   Food protein-induced proctocolitis
   Food protein-induced enteropathy syndrome
   Celiac disease
   Respiratory    Food induced pulmonary hemosiderosis
   (Heiner syndrome)
 
Contact urticaria

l wheal and flare reaction following external contact with a substance
l it usually appears within 30 min, and clears completely within hours, without residual   signs of irritation
l Classification
  1. Nonimmunological contact urticaria
  2. Immunological contact urticaria
  3. Mixed/undetermined contact urticaria
Nonimmunological contact urticaria (NICU)

l produce a reaction without any previous sensitization in most or almost all exposed
   persons

Pathogenesis
l not clearly understood
l appears to involve the release of vasogenic mediators without involvement of   immunological processes

  1. Dimethyl sulphoxide (DMSO)
    - damage blood vessels, making them leaky
    - cause mast cell degranulation
  2. sorbic acid, benzoic acid : release of prostaglandin D2 without concomitant histamine release
Diagnosis
l closed patch test
     - patches are removed after 15 min and reactions read at 20, 40, 60 min l open test
     - carried out on the arm or upper back, with most reactions evident by 45 min
     - erythema and edema have been mainly visually

Immunological contact urticaria (ICU)


l Type 1 hypersensitivity reaction, mediated by allergen-specific IgE in a previously
  sensitized individual
l contact urticaria syndrome : potential for multisystem involvement

Pathogenesis
l allergen penetration through the epidermis, then binding to IgE on mast cells
l causing degranulation and release of histamine and other vasoactive substances
l other inflammatory mediators such as prostaglandins, leukotrienes and kinins may
  also influence the clinical response

Diagnosis
l skin prick tests with fresh foods or commercially available reagents
l measurement of allergen specific IgE
l open application test

Treatment
l allergen avoidance
l antihistamine therapy for mild reactions
l self-administered adrenaline device for those with life-threatening reactions

 
Differences between ICU and NICU
    ICU   NICU
  Prior sensitization   Yes   No
  Elicitation time
  (open teat on skin)
  10-20 min   < 45 min
  Systemic features   Occasionally
  'Contact urticaria syndrome'
  No
  Common causes   Proteins   Simple chemicals
  Main mediator   Histamine   Ecosanoids?
  Inhibitors   Antihistamines, capsaicin   NSAIDS
  Diagnosis   Skin prick test
  Specific IgE assay
  Open/closed application test
 



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