Diagnosis of Asthma
Jonathan Cogen, MD, MPH
Introduction
•Asthma can be difficult to diagnose in children, particularly in those <5 years of age (see Chapter 43, Recurrent Wheezing in Infants, Toddlers, and Preschoolers).
•Many infants and toddlers wheeze during viral respiratory illnesses but do not go on to have asthma when they are older.
•The Asthma Predictive Index (API) was created to help forecast which children are more likely to have asthma later in life, which removes some ambiguity with this prognostic challenge.
•The API includes frequent wheezing during the first 3 years of life and either 1 major risk factor (parent history of asthma or child diagnosis of eczema) or 2 of 3 minor risk factors (blood eosinophilia, wheezing without colds, and allergic rhinitis).
•Children with a positive API were 4.3–9.8 times more likely to have active asthma between ages 6 and 13 than children with a negative API; children without API risk factors had a negative predictive value of 94% for the development of asthma at age 6.
•Misdiagnosis of asthma as pneumonia or bronchitis can lead to ineffective and unnecessary use of antibiotics.
•Overdiagnosis of asthma can result in unnecessary use of inhaled medications and oral steroids, as well as familial anxiety.
Clinical Features
•Typical signs and symptoms include
—Polyphonic wheezes, predominantly on expiration
—Recurrent and/or chronic cough
—Chest tightness
—Shortness of breath
•Specific triggers include
—Colds and viral illnesses
—Exercise
—Exposure to cold air
—Cough after laughing or crying
—Allergens, including pets, mold, dust mites, and additional environmental exposures
—Pollution (indoor or outdoor)
—Passive exposure to smoke
•Additional allergic comorbidities (dust mites, pollen, trees, grasses, etc)
occur in most children with asthma
•Cough is typically worse at night
•Parental or patient report of wheeze correlates poorly with physician-
diagnosed wheeze; thus, any diagnosis of wheezing should be confirmed by a medical provider.
•Additional physical examination findings include an increased chest anterior-posterior diameter, an expiratory abdominal push, and a prolonged expiratory phase on respiration.
Differential Diagnosis
•Alternative diagnoses (Table 25-1) should be considered when
—A patient is nonresponsive to standard asthma therapy (β2-agonists or inhaled or oral corticosteroids)
OR
—Certain red flags are present, including digital clubbing, stridor, fixed monophonic wheeze at examination, cyanosis, or cardiac findings, including a cardiac murmur or asymmetrical peripheral pulses
•Differential diagnosis includes
—Recurrent aspiration or dysphagia
—Vocal cord dysfunction
—Tracheal and/or bronchial malacia
—Cystic fibrosis
—Primary ciliary dyskinesia
•Although rare, providers should consider a pediatric pulmonary referral if a fixed airway obstruction is suspected, such as a vascular ring or sling, right-sided aortic arch, or endobronchial mass, if symptoms persist despite asthma therapy.
•Once asthma is diagnosed, the patient should be reassessed 4–6 weeks after therapy initiation to ensure symptom improvement.
Diagnostic Considerations
Pulmonary Function Testing (Spirometry)
•Pulmonary function testing can be used to support a diagnosis of asthma (Figure 25-1); most children with asthma, however, will have normal lung function.
•Spirometry is used to measure how much air the patient breathes in and out and how fast the air is exhaled.
—Spirometry can typically be performed in developmentally appropriate children by 5 years of age.
•Spirometric findings of obstructive lung disease include the ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) in the <5th percentile when compared to predicted values.
Adapted from Rosenthal M. Differential diagnosis of asthma. Paediatr Respir Rev. 2002;3:148–153. Copyright 2002, with permission from Elsevier.
•More typically, a FEV1/FVC ratio of <80% is used to denote an obstructive process consistent with asthma in children.
•A change in absolute value of percentage predicted FEV1 of ≥12% within 15 minutes after bronchodilator administration is considered a positive response and supports the diagnosis of asthma; a percentage predicted FEV1 change of <8% is considered a negative response.
•Once a diagnosis of asthma is established, the severity of lung function impairment is largely based on percentage predicted FEV1, as follows:
—Mild persistent (≥80%)
—Moderate persistent (60%–79%)
—Severe persistent (<60%)
•Consistent percentage predicted FEV1 values <60% typically warrant subspecialty consultation.
•A concomitant decrease in FEV1 and FVC is most commonly caused by poor patient effort but may rarely reflect airflow obstruction that can be better assessed with body plethysmography (Figure 25-1).
Figure 25-1. Example of an obstructive pattern at pulmonary function testing and a positive bronchodilator response consistent with obstructive lung disease (asthma). FEV1 = forced expiratory volume in 1 second. From National Heart, Lung, and Blood Institute. Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma. U.S. Department of Health and Human Services; 2007.
•A normal ratio of FEV1 to vital capacity, coupled with a percentage predicted vital capacity <80%, could be consistent with a restrictive pulmonary defect; subspecialty consultation (along with additional lung function testing, including body plethysmography) should be sought.
•Spirometry values should be assessed over time as a marker of improvement and adherence to therapy.
•Additional testing available in pediatric pulmonary or allergy subspecialty clinics includes
—Body plethysmography
—Airway hyperresponsiveness
—Bronchodilator or methacholine challenge testing
—Fractional exhalation of nitric oxide (FENO)
•Body plethysmography can also be used to assess the presence of an obstructive defect; a residual volume to total lung capacity ratio of >25% to 30% predicted is suggestive of air trapping and is consistent with an obstructive defect.
•FENO can be used to determine the likelihood of eosinophilic inflammation and steroid responsiveness in individuals with asthma.
•A low FENO (<20 parts per billion [ppb] in children) indicates that a patient might be less likely to respond to corticosteroids, while a high FENO (>35 ppb in children) is predictive of corticosteroid responsiveness.
Resources for Families
•How Is Asthma Diagnosed? (American Lung Association). www.lung.org/lung-health-and-diseases/lung-disease-lookup/asthma/diagnosing-treating-asthma/how-is-asthma-diagnosed.html
•Asthma Basics (KidsHealth). kidshealth.org/en/parents/asthma-basics. html
Clinical Pearls
•Asthma is a clinical diagnosis established by obtaining a thorough history and performing physical examination and spirometry testing.
•Assessment for reversibility with bronchodilator testing can aid in the diagnosis of asthma (see Chapter 4, Office Pulmonary Function Testing).
•An increase in the absolute value of percentage predicted FEV1 of ≥12% after bronchodilator administration is consistent with airway reversibility. With training, this evaluation for reversibility can be accomplished in a primary care office.
•In a subspecialist’s office, more complete pulmonary function testing and FENO can be used in support of a diagnosis of asthma.
•Be sure to rule out other certain diagnoses (eg, cystic fibrosis) if red flags—including digital clubbing or stridor—are present.
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