Peanut allergy

• Peanut allergy
  • estimated to affect about 1% of the population, although one recent study from the UK found a prevalence of 1.8% (1)
  • diagnosis
    • most often made during the second year of life
    • about 75% of reactions occur with the first known peanut exposure
  • expected natural course for peanut allergy is for life-long persistence in the majority of affected patients - note though that it has been shown in the past decade that about 20% of children with peanut allergy eventually outgrow their allergy
  • clinical features of peanut allergy
    • symptoms with initial reactions most commonly involve skin only, occurring in about 45-50%
    • about 2% develop only respiratory symptoms and 4% have only gastrointestinal involvement
    • two systems are involved in between 9% and 25%, and three systems in 11-21%
    • there is a tendency for reactions to become more severe over time
    • other atopic conditions occur frequently in peanut-allergic children
      • typically about 55-60% with allergic rhinitis
      • 60-75% with asthma
        • coexistent asthma is a risk factor for more severe peanut reactions, especially involving the respiratory tract
      • 60-75% with eczema
    • diagnosis of peanut allergy
      • based a history of clinical symptoms on exposure to the allergen along with the presence of peanut-specific IgE on testing
        • IgE can be detected either by skin prick test (SPT) or by measurement of serum peanut-specific IgE
        • positive predictive value for a positive SPT can clearly be quite low if the test is not used judiciously
        • serum peanut IgE can also be used in the evaluation of peanut allergy
        • studies have found that increasing serum peanut-IgE is more likely indicative of symptomatic allergy
  • management
    • if the diagnosis of IgE-mediated peanut allergy has been made, a self-injectable dose of adrenaline should always be available
    • adrenaline should be administered in all cases of anaphylaxis
      • intramuscular injection of adrenaline into the anterior-lateral thigh is considered the most appropriate route
    • oral antihistamines should be considered an adjunctive therapy, not an alternative to adrenaline
      
      
  • timing of dietary introduction of peanuts and development of peanut allergy
    • modelling study estimated 77% reduction in peanut allergy when peanut was introduced to diet of all infants (at 4 months with eczema; at 6 months without eczema) with a diminished reduction in peanut allergy with every month of delayed introduction (33% if delayed to 12 months) (3)

Tree nut allergy

• has been less clearly characterized than peanut allergy
  • in the USA and Europe, the most common tree nuts to which patients report allergy are walnut, cashew, almond, pecan, Brazil nut, hazelnut, macadamia nut, pistachio, and pine nut
• prevalence of allergy to tree nuts is estimated to be about half that of peanut allergy
• reactions tend to be severe
• 45% of tree nut allergic patients were allergic to more than one nut
• 25-50% of peanut allergic patients are also allergic to tree nuts
• overall, only 9% of those with a history of acute reactions to tree nuts passed a challenge
• results of SPT can also be used in making the decision of when food challenges are appropriate
  • increasing skin test size appears to correlate with increasing likelihood of true allergy

Notes:

• during adolescence, kissing can become a risky behavior of increased significance
  • cases of allergic persons experiencing allergic reactions through kissing are well-documented
    • a study assessed the risk of persistence of peanut antigen in the mouth, and what measures can help to lessen/eliminate it
      • specifically, the amount of peanut remaining in the oral cavity after ingesting a breakfast of two tablespoons of peanut butter on a sandwich was evaluated
        • one hour after ingestion, 13% of participants still had detectable levels
        • zero% had detectable levels after a peanut-free lunch.
      • brushing of teeth and/or rinsing of mouth immediately after the ingestion significantly reduced levels, but the majority of participants still had detectable levels. Waiting 60 min then brushing, or waiting 30 min then chewing gum resulted in a majority having undetectable levels, although a few remained detectable

Reference:

• (1) Hourihane JO et al. The impact of government advice to pregnant mothers regarding peanut avoidance on the prevalence of peanut allergy in united kingdom children at school entry. J Allergy Clin Immunol 2007: 119: 1197-202.
• (2) Skripak JM, Wood RA. Peanut and tree nut allergy in childhood. Pediatric Allergy and Immunology 2008; 19 (4): 368-373.
• (3) Roberts, Graham et al. Defining the window of opportunity and target populations to prevent peanut allergy. Journal of Allergy and Clinical Immunology, December 12th 2022.