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Chapter 135 Diagnosis of Allergic Disease
Dan Atkins, Donald Y.M. Leung
Allergic diseases arise from the acute or chronic exposure of a sensitized individual to a specific allergen by inhalation, ingestion, contact, or injection. Symptoms most often involve the nose, eyes, lungs, skin, or gastrointestinal tract either individually or in combination. A carefully obtained history, including environmental exposures, and the appropriate laboratory tests or allergen challenges, is critical for an accurate diagnosis.
Obtaining a complete history from the allergic patient involves eliciting a description of all symptoms along with their timing and duration, exposure to common allergens, and responses to previous therapies. Because patients often suffer from more than one allergic disease, the presence or absence of other allergic diseases, including allergic rhinitis, allergic conjunctivitis, asthma, food allergy, and atopic dermatitis, should be determined. A family history of allergic disease is common and is one of the most important factors predisposing a child to the development of allergies. The risk of allergic disease in a child approaches 50% when one parent is allergic and 66% when both parents are allergic.
Several characteristic behaviors are often seen in allergic children. Because of nasal pruritus and rhinorrhea, children with allergic rhinitis often perform the allergic salute by rubbing their nose upward with the palm of their hand. This maneuver gives rise to the nasal crease, a horizontal wrinkle over the bridge of the nose. Characteristic vigorous grinding of the eyes with the thumb and side of the fist is frequently observed in children with allergic conjunctivitis. The allergic cluck is produced when the tongue is placed against the roof of the mouth to form a seal and withdrawn rapidly in an effort to scratch the palate. The presence of other symptoms, such as fever, unilateral nasal obstruction, and purulent nasal discharge, suggests other diagnoses.
The timing of onset and the progression of symptoms are relevant. The onset of recurrent or persistent nasal symptoms coinciding with placement in a daycare center might suggest recurrent infection rather than allergy. When patients present with a history of episodic acute symptoms, it is important to review the setting in which symptoms occur as well as the activities and exposures that immediately precede their onset. Symptoms associated with lawn mowing suggest allergy to grass pollen or fungi, whereas if the symptoms always occur in homes with pets, then animal dander sensitivity is an obvious consideration. Reproducible reactions after the ingestion of a specific food raise the possibility of food allergy. When symptoms wax and wane but evolve gradually and are more chronic in duration, a closer look at whether the timing and progression of symptoms correlate with exposure to a seasonal aeroallergen is warranted.
Aeroallergens such as pollens and fungal spores, the concentrations of which in outdoor air fluctuate seasonally, are prominent causes of allergic disease. Correlating symptoms with the seasonal pollination patterns of indigenous plants along with information provided by local pollen counts can aid in identifying the allergen to which the patient is sensitized. Throughout most of the USA, trees pollinate in the early spring. Grasses pollinate in the late spring and early summer, whereas weeds pollinate in late summer through the fall. The presence of fungal spores in the atmosphere follows a seasonal pattern in the northern USA, with spore counts rising with the onset of warmer weather and peaking in the late summer months, only to recede again with the onset of colder weather in the late fall through the winter. In warmer regions of the southern USA, fungal spores and grass pollens may cause symptoms on a perennial basis.
Rather than experiencing seasonal symptoms, some patients suffer allergic symptoms year-round. In these patients, sensitization to sources of perennial allergens usually found indoors, such as dust mites, animal dander, cockroaches, and fungi, warrants consideration. Species of certain fungi, such as Aspergillus and Penicillium, are found indoors, whereas Alternaria is found in both indoor and outdoor environments. Cockroach allergens are often problematic in inner city environments. Patients sensitive to perennial allergens often also become sensitized to seasonal allergens and experience baseline symptoms year-round with worsening during the spring and fall pollen seasons.
The age of the patient is an important consideration in identifying potential allergens. Infants and young children are first sensitized to allergens that are in their environment on a continuous basis, such as dust mites, animal dander, and fungi. Clinically relevant sensitization to seasonal allergens usually takes several seasons of exposure to develop. Food allergies are more common in infants and young children, resulting primarily in cutaneous, gastrointestinal, and, less frequently, respiratory symptoms.
Complete information from all previous evaluations and prior treatments for allergic disease should be reviewed, including the response to all medications that have been used and the duration and impact of allergen immunotherapy. Improvement in symptoms during treatment with medications or therapies used to treat allergic disease provides additional evidence that the symptoms are the result of an allergic process.
A thorough environmental survey should be performed, with attention to potential sources of allergen and/or irritant exposure. The age and type of the dwelling, how it is heated and cooled, the use of humidifiers or air filtration units (either central or portable), and any history of flooding or water damage should be noted. Forced hot air heating may repeatedly stir up dust mite, fungi, and animal allergens. The irritant effects of wood-burning stoves, fireplaces, and kerosene heaters may provoke respiratory symptoms in allergic patients. Increased humidity or water damage in the home is often associated with greater exposure to dust mites and fungi. Carpeting serves as a reservoir for dust mites, fungi, and animal dander. The number of domestic pets and their movements about the house, including where they sleep, should be ascertained. Special attention should be focused on the bedroom, where a child spends a significant portion of time. The age and type of bedding, the number of stuffed animals, window treatments, and accessibility of the room to pets should be reviewed. The number of smokers in the home and where they smoke is useful information. Hobbies that might result in exposure to allergens or respiratory irritants such as paint fumes, cleansers, sawdust, latex, or glues should be identified. Similar information should be obtained in regard to other environments where the child spends large portions of time, such as a relative’s home, the classroom, or a daycare center.
In patients with asthma, a peak flow analysis or spirometry should be performed for evidence of airway obstruction. If respiratory distress is observed, pulse oximetry should be performed. The child presenting with a chief complaint of rhinitis or rhinoconjunctivitis should be observed for mouth breathing, paroxysms of sneezing, sniffing, and rubbing of the nose and eyes. Infants should be observed during feeding for nasal obstruction severe enough to interfere with feeding as well as for evidence of aspiration or gastroesophageal reflux. The frequency and nature of coughing that occurs during the interview and any positional increase in coughing or wheezing should be noted. Children with asthma should be observed for congested cough, tachypnea at rest, retractions, and audible wheezes. Patients with atopic dermatitis should be monitored for repetitive scratching and the extent of skin involvement.
Because children with severe asthma as well as those receiving oral corticosteroids may suffer growth suppression, an accurate height should be plotted at regular intervals. Poor weight gain in a child with chronic chest symptoms should prompt consideration of cystic fibrosis. The blood pressure should be measured to evaluate for steroid-induced hypertension. The patient with acute asthma may present with pulsus paradoxus, defined as a drop in systolic blood pressure during inspiration >10 mm Hg. Moderate to severe airways obstruction is indicated by a decrease of >20 mm Hg. An increased heart rate may be the result of an asthma flare or the use of a β-agonist or decongestant. Fever is not caused by allergy alone and should prompt consideration of an infectious process, which may exacerbate asthma.
Parents of allergic children are often concerned about blue-gray to purple discolorations beneath the lower eyelids, attributed to venous stasis and referred to as allergic shiners. They are found in up to 60% of allergic patients and almost 40% of patients without allergic disease. They are often accompanied by Dennie lines (Dennie-Morgan folds), which are prominent symmetric skin folds that extend in an arc from the inner canthus beneath and parallel to the lower lid margin.
In most patients with allergic conjunctivitis, involvement of the eyes is bilateral. Examination of the conjunctiva reveals varying degrees of conjunctival injection and edema. In severe cases, periorbital edema may involve primarily the lower eyelids be observed. The classic discharge associated with allergic conjunctivitis is usually described as “stringy” or “ropy.” In children with vernal conjunctivitis, examination of the tarsal conjunctiva may reveal cobblestoning. Children repeatedly receiving large doses of oral corticosteroids for management of severe asthma are at risk for development of posterior subcapsular cataracts. Keratoconus, or protrusion of the cornea, may occur in patients with atopic dermatitis as a result of repeated trauma produced by persistent rubbing of the eyes.
The external ear should be examined for eczematous changes in patients with atopic dermatitis. Because otitis media with effusion is common in children with allergic rhinitis, pneumatic otoscopy should be performed to evaluate for the presence of fluid in the middle ear and to exclude infection.
Examination of the nose in allergic patients often reveals the presence of a transverse nasal crease on top of the nose at the junction of the cartilaginous and bony portions of the nasal bridge, which is caused by frequent rubbing of the nose. Nasal patency should be assessed, and the nose examined for structural abnormalities affecting nasal airflow, such as a septal deviation, turbinate hypertrophy, septal spurs, and nasal polyps. Decrease or absence of the sense of smell should raise concern about the presence of nasal polyps, a feature of cystic fibrosis. The nasal mucosa in allergic rhinitis is classically described as pale to purple in comparison with the beefy red mucosa of patients with nonallergic rhinitis. Allergic nasal secretions are typically thin and clear. Purulent secretions suggest another cause of rhinitis. The frontal and maxillary sinuses should be palpated to identify tenderness to pressure that might be associated with sinusitis.
Examination of the lips may reveal cheilitis caused by drying of the lips from continuous mouth breathing and repeated licking of the lips in an attempt to replenish moisture and relieve discomfort. Tonsillar and adenoidal hypertrophy along with a history of impressive snoring raises the possibility of obstructive sleep apnea. The posterior pharynx should be examined for the presence of postnasal drip and posterior pharyngeal lymphoid hyperplasia.
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