Asthma: Diagnosing Kids

Case

A 4-year-old boy presents to clinic with a few days of fever, congestion, cough, and wheezing. He has received albuterol twice in the ED for similar presentations. His older brother has a diagnosis of asthma and uses an albuterol inhaler. The parents gave the patient his brother’s inhaler a few times over the past days and they think it helped a little. His parents ask if the patient also has asthma.

Presentation

Asthma is defined by episodic and reversible airway constriction and inflammation in response to infection, environmental allergens, and irritants.

Recurrent cough and wheezing are the most common presenting symptoms of asthma in children, noting that parental reports of wheezing are often unreliable and may more often reflect noisy breathing.

  • Characteristic recurrent features of asthma-induced cough include occurrence at night, during certain seasons, in response to specific exposures (e.g., cold air, exercise, etc.) laughing, allergen exposure, or crying), or a cough lasting more than 3 weeks, especially after an acute respiratory infection
  • Other common symptoms include shortness of breath, chest tightness, chest pain, fatigue, and even poor school performance

Wheezing is the characteristic finding on exam, and tends to be polyphonic.

Asthma affects around 1 in 12 children in the US, but prevalence in black children is approximately twice that of white children. Furthermore, black children have the highest asthma morbidity and mortality rates of any US group, with twice the ED visit/hospitalization rate and 9 times the mortality rate as white children.

Risk factors

Multiple known risk factors for asthma:

  • Atopy (allergic rhinitis, eczema)
  • Family history of asthma
  • Passive tobacco exposure*
  • Environmental allergens or pollutants

*A 2012 meta-analysis found that prenatal and postnatal secondhand smoke exposure was associated with 21-85% increase risk in asthma, with the strongest effect occurring in prenatal maternal smoking on asthma in children aged ≤2 years of age.

Triggers

There’s a LONG list of potential triggers of asthma exacerbations:

  • Respiratory viral infections (most common trigger overall)**
  • Environmental smoke (tobacco, candles, incense, marijuana, electronic cigarettes, wood fires, charcoal fires, etc.)
  • Air pollution and particulate matter (dust, construction sites, perfumes, paints, soaps, cleaning products)
  • Perennial allergens (mold spores, cockroaches, rats, mice, dust mites, and pet dander)
  • Seasonal allergens (tree, weed, and grass pollens)
  • Weather (rapid changes or extreme cold/hot air)
  • Strong emotions (laughter, crying, or anger)
  • Medications (beta blockers, aspirin, NSAIDs)
  • Exercise and other strenuous activity

**Specific viral infections have been found to be associated with increased exacerbation severity (e.g., rhinovirus subtype C and influenza A H1N1) and treatment failure (RSV, influenza, and parainfluenza).

Many Things Can Wheeze!

Wheezing is common, and has been shown to affect half of all preschool children, although only one third go on to develop asthma. And the differential for wheezing is broad:

Acute:

  • Bronchiolitis
  • Viral-induced wheeze
  • Foreign body aspiration
  • Atypical pneumonia (mycoplasma)
  • Tracheitis
  • Bronchitis

Chronic:

  • Structural:
    • Vascular rings
    • Tracheal stenosis/webs
    • Tracheo-bronchomalacia
    • Tumors
    • Lymphadenopathy
    • Cardiomegaly
  • Functional:
    • GERD
    • Cystic Fibrosis
    • Recurrent aspiration
    • Immunodeficiency
    • Primary Ciliary Dyskinesia
    • Bronchopulmonary dysplasia
    • Interstitial Lung Disease
    • Pulmonary Edema

Predictive Models

There are many predictive models for asthma. A 2015 systematic review of 12 such models assessing symptomatic children up to four years of age revealed a number of predictive factors, but no model had both high sensitivity and specificity. Similarly, a 2020 systematic review of 26 such models found that they demonstrated moderate ability to either rule in or rule out asthma development, but not both. In sum, the role of these tools us to help identify young children at high risk of developing asthma, not as criteria for diagnosis.

One of these models is the Asthma Predictive Index (API), which applies to children 3 years and younger. The API is one of the few predictive models that has been externally validated, and its use was endorsed in the 2007 NAEPP Guideline for the Diagnosis and Management of Asthma. But its sensitivity is low, suggesting that the test is poor at predicting later asthma; however, its negative predictive value is high, suggesting utility in identifying children that have a low probability of having later asthma when the API is negative. Confusingly, there are multiple modified versions of the API including the modified API (mAPI), which appears to have stronger positive predictive value but requires allergic testing.

Source: UpToDate

Pulmonary Function Testing

Pulmonary function testing (PFTs) is an important component of the diagnostic evaluation of a child in whom there is a clinical suspicion of asthma. There is no age cutoff for performing PFTs, although children younger than 5 years of age are typically unable to provide the effort required to reliably complete testing.

Two important spirometry readings in the diagnosis and evaluation of asthma are forced expiratory volume in 1 second (FEV1) and the ratio of FEV1 to forced vital capacity (FEV1/FVC).

The goal of PFTs in evaluating asthma is to document expiratory flow limitation or obstruction with reversibility. An FEV1/FVC ratio <0.80 is diagnostic for airflow obstruction, and reversibility with administration of a bronchodilator is diagnostic for asthma. The classic flow-volume curve for asthma shows a dampening and scooping out of the expiratory curve.

Diagnosis

Asthma in children remains largely a clinical diagnosis. Consider the following algorithm for a child with respiratory symptoms suggestive of asthma:

Source: Patel et al. Asthma. Pediatr Rev. 2019
  • A child with a family history of asthma presenting with episodic and recurring chest tightness, cough, difficulty breathing, or wheezing in response to common triggers who also demonstrates improvement with a SABA likely has asthma
  • In older children, demonstration of reversible bronchospasm on PFTs is diagnostic for asthma

Take-Home Points!

  • Asthma is a chronic lung disease caused by bronchoconstriction and inflammation
  • History is a significant part of the diagnostic work-up: personal history of atopic conditions, family history of atopy (allergic rhinitis, eczema, asthma), passive tobacco exposure, environmental allergens or pollutants
  • Most common symptoms are cough and wheezing, but don’t overlook other signs like fatigue, exercise avoidance, and even poor school performance
  • PFTs show an obstructive pattern that can be reversed with a bronchodilator
  • Predictive models may be helpful in evaluating children for asthma but are not diagnostic on their own

Blog post based on Med-Peds Forum talk by Katherine Hobbs, PGY1, and Athena Manatis-Lornell, PGY1

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