Allergic Symptoms

Chapter 19 Allergic Symptoms



Jerold C. Woodhead




ETIOLOGY



What Is Allergy?


Allergy is the term for the symptoms that develop as the result of four distinct immunopathologic mechanisms of tissue damage, classically referred to as type I to IV reactions in the Gell and Coombs classification: anaphylaxis (type I), cytotoxic (type II), immune complex (type III), and cell mediated (type IV). Allergens such as dust, pollen, molds, animal dander, and foods can cause allergic reactions when their antigenic properties trigger immunologic responses in susceptible individuals. Allergenic substances also include antibiotics or other medications, insect venom, and latex. The most common allergic reaction is an IgE-mediated antigen-antibody response (type I reaction) that can produce anaphylaxis, urticaria, rhinitis, asthma, and atopic dermatitis. Although characteristic of allergic responses, these reactions may also result from nonallergic mechanisms. Furthermore, a single antigen can cause any of the four types of allergic reactions. As an example, penicillin causes anaphylaxis (I), hemolysis (II), serum sickness (III), and skin sensitivity (IV). Common skin sensitizations include the rash caused by contact with poison ivy and the reaction to tuberculin in a patient who has latent tuberculosis.



How Does the Type I Reaction Cause Symptoms?


A type I allergic reaction most commonly develops when a susceptible individual becomes “sensitized” by exposure to an allergen that contacts a mucosal surface in the conjunctiva, nasal airway, pharynx, or upper or lower airway. An allergen may also be ingested or inoculated onto abraded skin. The allergen then induces B lymphocytes to secrete antigen-specific IgE, which binds to mast cells and basophils. These sensitized cells react to subsequent allergen exposure by releasing preformed mediators, primarily histamine. Other mediators that can develop during reexposure to allergens include leukotrienes, cytokines, enzymes, and chemotactic agents. The various mediators cause dilation of blood vessels, increase in vascular permeability, secretion of mucus, and contraction of smooth muscles. Symptoms such as sneezing, rhinorrhea, wheezing, and itching develop promptly after reexposure to an allergen. In addition, allergen reexposure can also trigger late activation of cell-mediated inflammation, which develops 2 to 4 hours after exposure and results in reactions lasting at least 24 hours. Late reactions promote persistent bronchodilator-resistant airway obstruction, increased airway hyperreactivity, and chronic nasal obstruction. Eosinophils are the most common cell type involved at the start of the late reaction, but any of the inflammatory leukocytes may participate.



Are Allergies Common in Childhood?


More than one-third of all children experience allergic rhinitis; up to 10% to 15% have some degree of “eczema,” ranging from patches of dry skin to severe atopic dermatitis; and 5% to 10% experience asthma. Food allergies occur less frequently than respiratory allergies. They tend to be most common early in life and may persist into adulthood. Anaphylaxis, though uncommon, can be life threatening.



What Symptoms Occur in Allergy?


Allergy is often brought up as an explanation for a child’s symptoms, but careful evaluation is needed to identify the true cause. Many problems that are labeled as being “allergic” often cannot be demonstrated to result from a true allergic reaction. Chronic rhinitis, for example, is often labeled as having an allergic cause, but recurrent viral infection, not allergy, probably accounts for the majority of cases. Adverse reactions to foods are also often labeled as allergic, although most are not. A specific allergic cause for most eczema cannot be identified. Asthma can have an allergic basis, but not all does. In addition to the specific manifestations caused by allergic reactions, nonallergic sequelae are common in allergic children, including otitis media, conjunctivitis, pneumonia, and skin infections. You must be prepared to evaluate and manage both the allergic and nonallergic forms of these problems.



What Is “Atopy” and How Does It Manifest?


The term atopy was originally coined by Coca to describe the type of abnormal hypersensitivity associated with anaphylactic-type reactions. It is currently used to label IgE-mediated allergic reactions (type I) that cause upper or lower airway disease and the syndrome of atopic dermatitis. The most common manifestations of atopy are asthma, conjunctivitis, atopic dermatitis, and rhinitis. The presence of one atopic disorder increases the likelihood that a patient will have another. For example, more than half of asthmatic children have allergic rhinitis and approximately half of children with atopic dermatitis have asthma. Interestingly, infants with asthma do not typically have allergic rhinitis. Atopy has a strong hereditary tendency: more than two-thirds of children will manifest atopic findings if both parents are atopic.



EVALUATION



How Do I Know if My Patient Has an Allergy?


History provides the key information. The patient’s symptoms will allow you to determine whether the common target organs of allergic reactions are involved. These target organs include the nasopharyngeal and ocular mucosa, the airway and lungs, the skin, and the gastrointestinal tract. Age of the patient, exposures, seasonality, timing, and duration of symptoms all help with the diagnosis.



Do Allergic Manifestations Vary by Age?


Most allergies occur in school-age children or adolescents who have chronic or recurrent nasal congestion, runny nose, sneezing, itchy eyes, or cough and wheezing. Infants and younger children may have persistent or recurrent rash, protracted colds, or cough and wheezing. If cough and/or wheezing are prominent complaints, inquire about nighttime cough, reduced physical stamina, and a sensation of chest tightness (see Asthma in Chapter 69). Recurrent otitis media may prompt parents to raise the question of allergy, particularly if the child has chronic rhinitis; most commonly, however, the otitis is a consequence of recurrent viral infections.



What Exposures Trigger Allergic Reactions?


Onset of symptoms following specific exposures can help identify the allergen, especially if repeated events are documented. Occasionally an infant will develop bloody diarrhea, a reaction to milk protein that may have an allergic basis, although the exact mechanism is not yet known. The nutritional history and the family allergy history assume importance, but you must also ask questions about possible infection. Rarely, you will encounter a patient who has an anaphylactic reaction to a bee sting, peanuts, or another food. In this case, identification of the inciting allergen is crucial for future prevention and management. Seasonality or association with a specific environmental exposure also gives clues: symptoms may recur at a particular time of the year (e.g., ragweed allergy in late summer–early fall) or with an identifiable exposure (e.g., a pet cat). Information about the home heating system, presence of dust-trapping materials in bedrooms, and presence of pets is important. A damp basement or use of a humidifier may cause the home to have excessive humidity that promotes the growth of molds and dust mites. When a specific trigger for allergic symptoms cannot be easily identified, or when symptoms are year-round, the history must be thorough to ensure that all possibilities are considered.



How Does Family History Help with Diagnosis?


More than half of children with allergic symptoms and signs have a parent or sibling who also has allergy. Any child whose family history includes anaphylaxis or other severe allergic manifestations to specific food or environmental allergens should avoid exposure whenever possible.



How Do I Distinguish Allergy from Infection?


Duration of symptoms may give important clues to diagnosis: allergic rhinitis symptoms may persist for weeks, whereas viral upper respiratory infections typically last 5 to 7 days, although approximately 15% of children have viral symptoms that persist up to 10 to 14 days. Preschool children commonly have an average of eight upper respiratory infections per year, most in the span from November to May, so recurrent and persistent infections may confound the evaluation of chronic rhinitis. Physical examination should search for allergic signs that allow discrimination between allergy and infection or other causes of the findings.



What Am I Likely to Find on Head, Eyes, Ears, Nose, and Throat (HEENT) Examination?


When allergy causes nasal, pharyngeal, and ocular symptoms, the affected mucosal surfaces are typically pale and edematous, with a “cobblestone appearance” caused by lymphoid follicular hyperplasia. Mucosal inflammation is not as intense as that associated with viral or bacterial infection. Allergic rhinitis produces a watery nasal discharge, persistently obstructed nasal airway, mouth breathing, a denasal voice (loss of nasal resonance with inability to pronounce “M” and “N”), “train tracks” of thick white or yellow discharge in the posterior pharynx, and a throat-clearing sound or cough. These findings also all often accompany chronic rhinitis, of which only some is allergic. “Throat clearing” may reach such a frequency that it becomes tic-like or may develop into a “habit cough.” The allergic face includes open mouth, dark puffy eyelids (“allergic shiners”), and nasal discharge. The nasolacrimal ducts often become obstructed in allergic rhinitis, resulting in increased lacrimation, a “tear lake,” and a crusted, mucousy, and “gritty” eye discharge. This discharge is often misdiagnosed as bacterial conjunctivitis, even though conjunctival inflammation may not be a prominent finding. Secondary bacterial infection can develop with obstructed nasolacrimal ducts or with allergic conjunctivitis, but this will be marked by prominent conjunctival inflammation and usually a truly purulent discharge. An “allergic crease” on the nose reflects chronic rubbing of the nose to relieve itching or remove discharge; the “allergic salute” uses the hand to wipe the nose upward.

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Jun 19, 2016 | Posted by in PEDIATRICS | Comments Off on Allergic Symptoms

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