Louisville Medicine Volume 66, Issue 2 - Page 21

FEATURE IT’S JUST MY ALLERGIES…OH REALLY?! PART 1 History and Pathophysiology of Allergic Diseases F. Tolis Simon, MD N asal upper airway symptoms affect millions of Americans and pa- tients are affected for many years. The pathophysiology, differential diagnosis and associated condi- tions including the oral allergy syndrome are all important to consider when treating patients with “just allergies.” BACKGROUND AND PATHOPHYSIOLOGY Allergic rhinitis is characterized by nasal congestion, sneezing, nasal pruritus, and rhinitis that is due to environmental allergen exposure in susceptible individuals. It has a prevalence of 15 percent based on physician diagnosis in the United States depending on age, and this is thought to be increasing. (1) Exposure to both indoor and outdoor allergens cause symptoms in the person with the appro- priate genetic predisposition. A family history of allergy, asthma or atopic dermatitis confers significant risks to an individual. Studies have shown that if one parent is atopic, the risk may be 30 percent, and if both parents are atopic, the risk can be estimated to be as high as 50 percent. If neither parent is allergic, the risk decreases to 20 percent. (1, 3) The environment and allergen exposure are also important, as described by the hygiene hypothesis. (1, 3) In this mechanism, individuals develop an allergic t-helper subtype 2 (TH2) response if one is exposed to a “sterile environment” in which bacteria are not present, causing the immune system to mount less of a response to infection and more of an allergic IgE response to environmental allergens. Conversely, if an individual is in less of a “sterile environ- ment” and is exposed to bacteria, such as endotoxin, the immune system switches its focus to fighting infection and is stimulated to make a t-helper subtype 1 (TH1) response to fight pathogens to protect the individual and less TH2 allergen response is made. Once the allergic TH2 response is established, IgE production occurs and mast cells become covered with IgE on their surface leading to sensitization. Upon re-exposure to allergen, crosslinking of IgE occurs with subsequent immediate mast cell degranulation of histamine, leukotrienes, cytokines and other mediators trigger- ing further activation of the immune system characterized by late phase cellular inflammation. (1) Atopy becomes the issue and can be characterized by increased risk of atopic dermatitis, food allergy, allergic rhinitis and asthma. Table I summarizes risk factors for the development of allergic rhinitis. (1, 3) TABLE I. RISK FACTORS FOR ALLERGIC RHINITIS Increased Risk Decreased Risk Family History of Allergy Increased Numbers of Siblings Serum IgE >100 Iu/ml before age 6 Grass Pollen Count Higher Social Economic Class Farm Environment Positive allergy prick skin test Mediterranean diet (High in antioxidant and Omega 3 fatty acids) Maternal smoking Particulate air pollution Co-morbidities associated with allergic rhinitis include allergic con- junctivitis, eustachian tube dysfunction, chronic sinusitis, asthma, obstructive sleep apnea, decreased quality of life, poor school and work performance, and potentially other conditions. (1, 3) ALLERGEN EXPOSURE AND AVOIDANCE As things relate closer to home, the allergen exposure in Louisville is important to recognize. Louisville consistently ranks in the top five allergic cities to live in based on our high pollen counts and our climate in the Ohio Valley with lush vegetation, particularly Bluegrass. (4) According to the Allergy and Asthma Foundation of America (AAFA) in 2014, Louisville led the nation as the most difficult place to live with springtime allergy. In 2018, Louisville rated second. (4) The recognition of high pollen counts causing individuals to suffer with allergic symptoms has been widely noted. Some helpful measures to reduce pollen exposure are to keep windows and doors closed and use air conditioning. Participation in outdoor activities should be in the early morning or in the late evening when pollen counts are lower. (3) Tree pollination typically starts in mid-Feb- (continued on page 20) JULY 2018 19