If a cough is curable with antitussives (anti-cough medications), does it rule out asthma?

Response to Cough Controlled by Antitussives Does NOT Rule Out Asthma

A cough that responds to antitussive medications (like codeine or dextromethorphan) does NOT exclude asthma as the underlying diagnosis. In fact, asthma-related cough often requires specific anti-asthmatic therapy (inhaled corticosteroids and bronchodilators) for definitive resolution, and symptomatic improvement with antitussives merely masks the underlying airway inflammation without treating it 1.

Why Antitussive Response is Misleading

• Antitussives suppress the cough reflex centrally without addressing the underlying pathophysiology that triggers the cough 2, 3.
• Asthma causes cough through airway inflammation and bronchial hyperresponsiveness, mechanisms that antitussives do not treat 1.
• The diagnosis of cough-variant asthma (CVA) is only confirmed after resolution of cough with specific antiasthmatic therapy, not with symptomatic antitussive treatment 1.

The Correct Diagnostic Approach

Step 1: Systematic Evaluation for Asthma

• Medical history alone is unreliable for ruling in or ruling out asthma as a cause of chronic cough 1.
• Perform spirometry first to assess for reversible airflow obstruction 1.
• If spirometry is normal, bronchoprovocation challenge (BPC) with methacholine should be performed to detect bronchial hyperresponsiveness 1.
• A negative BPC has a negative predictive value close to 100%, effectively ruling out asthma 1.
• A positive BPC has a positive predictive value of 60-88%, warranting a trial of anti-asthmatic therapy 1.

Step 2: Therapeutic Trial for Asthma

• Initiate treatment with inhaled corticosteroids (ICS) plus inhaled β-agonists as first-line therapy for suspected asthmatic cough 1, 4.
• Expect at least partial improvement within 1 week, but complete resolution may require up to 8 weeks of treatment 1.
• If response is incomplete with ICS and bronchodilators, add a leukotriene receptor antagonist (such as montelukast) before escalating to oral corticosteroids 1.
• For severe or refractory cases, a short course of oral corticosteroids (prednisone 40 mg daily for 5-10 days) may be necessary to confirm the diagnosis 1.

Critical Pitfall to Avoid

Do not conclude that asthma is absent simply because antitussives provide symptomatic relief. This is a common error that delays appropriate diagnosis and treatment 1. Antitussives like codeine and dextromethorphan are non-specific suppressants that work on any cough, regardless of etiology 2, 3, 5.

When Asthma Treatment Should Be Pursued

• Asthma should always be considered as a potential etiology in any patient with chronic cough, even without wheezing or dyspnea 1.
• Cough-variant asthma presents with cough as the sole or predominant symptom, making clinical suspicion essential 1.
• Physical examination and spirometry may be entirely normal in CVA, necessitating BPC for diagnosis 1.

The Sequential Algorithm When Asthma is Suspected

1. After treating upper airway cough syndrome (UACS) with first-generation antihistamine/decongestant combinations, evaluate for asthma next 1, 4.
2. Perform BPC if available; if unavailable, proceed with empiric anti-asthmatic therapy 1.
3. If asthma treatment fails after adequate trial (including oral corticosteroids), consider non-asthmatic eosinophilic bronchitis (NAEB) with induced sputum testing for eosinophils 1.
4. If UACS, asthma, and NAEB have been adequately addressed without resolution, initiate empiric treatment for gastroesophageal reflux disease (GERD) 1, 4.

Key Distinction: Symptomatic vs. Definitive Treatment

• Antitussives provide symptomatic relief only and should be reserved for when definitive therapy cannot be given or when cough interferes with quality of life despite specific treatment 2, 3, 5.
• Definitive treatment depends on determining the underlying etiology and initiating specific therapy directed at that cause 2, 6.
• In asthma, definitive treatment is anti-inflammatory therapy with corticosteroids, not cough suppression 1.