Yes, Asthma is Highly Likely and Should Be Your Primary Diagnostic Consideration
Asthma should always be considered as a potential etiology in any patient with chronic cough, particularly when accompanied by exertional dyspnea, as asthma accounts for 24-29% of chronic cough cases in adult nonsmokers. 1, 2
Understanding Cough-Variant Asthma (CVA)
Your patient's presentation is classic for cough-variant asthma, where chronic cough is the predominant or sole symptom without the typical wheezing or dyspnea at rest. 1, 2
Key clinical features that support this diagnosis:
- Chronic nonproductive cough as the primary manifestation 1, 2
- Exercise-induced symptoms (difficulty breathing after exercise strongly suggests bronchial hyperresponsiveness) 1, 3
- Physical examination and spirometry may be entirely normal at rest, making diagnosis challenging but not excluding asthma 1, 2
Diagnostic Approach
If spirometry shows reversible airflow obstruction, proceed directly to empiric asthma therapy. 1 However, since CVA patients often have normal baseline spirometry, you need bronchoprovocation testing.
Perform methacholine inhalation challenge testing to document bronchial hyperresponsiveness when physical examination and spirometry are non-diagnostic. 1, 2
Critical Diagnostic Nuances:
- A positive methacholine test is consistent with but NOT diagnostic of CVA 1
- A negative methacholine test essentially excludes asthma due to its very high negative predictive power 1
- Definitive diagnosis requires documented resolution of cough with antiasthmatic therapy 1, 2
Common Pitfall to Avoid:
Do not assume a positive methacholine test alone confirms CVA—other conditions like postinfectious cough can also cause transient bronchial hyperresponsiveness. 1 The diagnosis is only confirmed when cough resolves with treatment.
Treatment Algorithm
Initiate inhaled bronchodilators and inhaled corticosteroids as first-line therapy. 1
Expected Treatment Response Timeline:
- Partial improvement after 1 week 4
- Complete resolution may require up to 8 weeks 4
- Most patients respond to inhaled bronchodilators and inhaled corticosteroids 1
If Initial Therapy Fails:
Add leukotriene receptor antagonists (montelukast), which appear particularly effective in treating asthmatic cough 1
Consider a short course of oral corticosteroids for refractory cases 1
Exercise-Induced Component
Your patient's exertional dyspnea warrants specific attention:
- Exercise triggers asthma in most individuals with chronic asthma 3, 5
- Pre-exercise short-acting β2-agonists (SABAs) are recommended as first-line therapy for exercise-induced symptoms 5, 6
- Patients should have rescue SABA available during exercise 7
Important FDA Labeling Caveat:
Montelukast (if used) is not indicated for acute bronchospasm reversal—patients must have short-acting inhaled β-agonist rescue medication available. 7
Clinical Course and Prognosis
Isolated cough may serve as a precursor to typical asthmatic symptoms developing later. 1, 2 Approximately 30% of CVA patients may develop typical bronchial asthma within several years, though in some patients cough remains the sole symptom indefinitely. 2
When to Refer
If asthma remains uncontrolled despite inhaled corticosteroids plus additional controller therapy, refer for specialized treatment. 8