How do you diagnose exercise-induced asthma?

Diagnosing Exercise-Induced Asthma

To diagnose exercise-induced asthma (EIA) or exercise-induced bronchoconstriction (EIB), perform standardized bronchoprovocation challenge testing rather than relying on self-reported symptoms or therapeutic trials without objective confirmation. 1

Initial Assessment

• Evaluate symptoms that suggest EIB:

  • Chest tightness
  • Shortness of breath
  • Coughing
  • Wheezing
  • Fatigue
  • Prolonged recovery times after exercise 2

• Perform baseline spirometry/pulmonary function testing (PFT) to:

  • Establish baseline lung function
  • Determine if underlying asthma is present
  • Rule out other pulmonary conditions 1, 3

Diagnostic Testing Algorithm

For patients without current clinical asthma:

1. Confirm normal to near-normal baseline PFT results
2. Verify no significant response to bronchodilator
3. Perform an indirect ungraded challenge test (preferred):
   • Exercise challenge on treadmill or cycle
   • Eucapnic voluntary hyperventilation (EVH) - preferred for athletes 1

For patients with known asthma:

1. Use an indirect graded challenge (e.g., mannitol, if available) for safety reasons
2. If negative but EIB still suspected, consider an ungraded challenge 1

Exercise Challenge Protocol Requirements

• Ensure adequate ventilation during testing:

  • At least 60% of maximum voluntary ventilation using dry medical grade air
  • If ventilation cannot be measured, ensure heart rate reaches:
    • At least 85% of maximum heart rate in adults
    • At least 95% of maximum heart rate in children and elite athletes 1
  • Maintain this level for 6 minutes after 2-4 minutes of ramping up 1

• Measure FEV1 at specific intervals:

  • Baseline measurement before exercise
  • Measurements at 3,5,10,15, and 30 minutes post-exercise
  • A 10% or greater decrease in FEV1 from baseline at any two consecutive time points within 30 minutes of stopping exercise confirms EIB diagnosis 1

Differential Diagnosis Considerations

When EIB is suspected but not confirmed, consider:

1. Exercise-induced laryngeal dysfunction (EILD):

   • Differentiate using appropriate challenge tests and flexible laryngoscopy during exercise 1
   • Look for inspiratory stridor vs. expiratory wheezing

2. Exercise-induced hyperventilation:

   • Perform cardiopulmonary exercise testing, especially in children and adolescents 1

3. Other respiratory conditions:

   • COPD, obesity, skeletal defects, diaphragmatic paralysis, or interstitial fibrosis 1

4. Exercise-induced anaphylaxis:

   • Consider when respiratory symptoms are accompanied by systemic symptoms (pruritis, urticaria, hypotension) 1

5. Cardiac conditions:

   • Refer to cardiologist when breathlessness with exercise and/or chest pain might be cardiac in origin 1

6. Psychological factors:

   • Consider psychological evaluation when hyperventilation and anxiety disorders are in the differential 1

Common Pitfalls and Caveats

1. Avoid empiric treatment without diagnosis:

   • Do not prescribe bronchodilators based on symptoms alone without confirmatory testing 3

2. Recognize limitations of direct challenges:

   • Methacholine challenge is less sensitive for detecting EIB than indirect challenges 1
   • Indirect challenges (exercise, EVH, mannitol) are preferred for diagnosing EIB 1

3. Understand prevalence context:

   • EIB affects 12-15% of general population 4, 2
   • Higher prevalence in elite athletes, especially in cold weather sports 5

4. Consider impact on quality of life:

   • EIB can prevent patients from participating in exercise
   • Associated with feelings of fearfulness, frustration, isolation, depression, and embarrassment 4

By following this diagnostic approach, you can accurately identify exercise-induced asthma and distinguish it from other conditions that may present with similar symptoms during exercise, allowing for appropriate treatment and improved quality of life.