Atlas of pathophysiology, 2 Edition

Part II - Disorders

Immunologic Disorders

Allergic rhinitis

Allergic rhinitis is a reaction to airborne (inhaled) allergens. Depending on the allergen, the resulting rhinitis and conjunctivitis may occur seasonally (hay fever) or year-round (perennial allergic rhinitis). Allergic rhinitis is the most common atopic allergic reaction, affecting over 20 million U.S. residents.

Age Alert

Allergic rhinitis is most prevalent in young children and adolescents, but occurs in all age groups.

Causes

·   Immunoglobulin (Ig) E-mediated type I hypersensitivity response to an environmental antigen (allergen) in a genetically susceptible person

Common triggers

·   Wind-borne pollens:

§  Spring—oak, elm, maple, alder, birch, cottonwood

§  Summer—grasses, sheep sorrel, English plantain

§  Autumn—ragweed, other weeds

·   Perennial allergens and irritants:

§  Dust mite excreta, fungal spores, molds

§  Feather pillows

§  Cigarette smoke

§  Animal dander

Pathophysiology

During primary exposure to an allergen, T cells recognize the foreign allergens and release chemicals that instruct B cells to produce specific antibodies called IgE. IgE antibodies attach themselves to mast cells. Mast cells with attached IgE can remain in the body for years, ready to react when they next encounter the same allergen.

The second time the allergen enters the body, it comes into direct contact with the IgE antibodies attached to the mast cells. This stimulates the mast cells to release chemicals, such as histamine, which initiate a response that causes tightening of the smooth muscles in the airways, dilation of small blood vessels, increased mucus secretion in the nasal cavity and airways, and itching.

Signs and symptoms

Seasonal allergic rhinitis

·   Paroxysmal sneezing

·   Profuse watery rhinorrhea; nasal obstruction or congestion

·   Pruritus of nose and eyes

·   Pale, cyanotic, edematous nasal mucosa

·   Red, edematous eyelids and conjunctivae

·   Excessive lacrimation

·   Headache or sinus pain

·   Itching of the throat

·   Malaise

Perennial allergic rhinitis

·   Chronic nasal obstruction, commonly extending to eustachian tube

·   Conjunctivitis and other extranasal effects rare

Clinical Tip

In both types of allergic rhinitis, dark circles may appear under the patient's eyes (“allergic shiners”) because of venous congestion in the maxillary sinuses.

Diagnostic test results

A definitive diagnosis is based on the patient's personal and family history of allergies as well as physical findings during a symptomatic phase.

·   Microscopic examination of sputum and nasal secretions reveals large numbers of eosinophils.

·   Blood chemistry shows normal or elevated IgE.

·   Skin testing paired with tested responses to environmental stimuli pinpoints the responsible allergens given the patient's history.

Treatment

·   Antihistamines such as fexofenadine

·   Inhaled intranasal steroids, such as beclomethasone, flunisolide, and fluticasone

·   Immunotherapy or desensitization with injections of extracted allergens

·   Nasal decongestants

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REACTION TO ALLERGEN EXPOSURE

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