What is cough variant asthma?

What is Cough Variant Asthma?

Cough variant asthma (CVA) is a distinct subtype of asthma where chronic cough is the predominant or sole symptom, occurring without the typical asthmatic symptoms of wheezing or dyspnea. 1

Definition and Clinical Presentation

CVA represents a unique clinical entity in which patients experience persistent, nonproductive cough as their only manifestation of asthma. 1 This condition differs fundamentally from typical asthma in several ways:

• Patients with CVA have a significantly more sensitive cough reflex compared to those with typical asthma or healthy individuals. 1
• Despite hypersensitive cough receptors, CVA patients demonstrate a lesser degree of bronchial hyperresponsiveness to methacholine compared to typical asthma patients. 1
• Physical examination and spirometry findings may be entirely normal, making diagnosis challenging. 1

Epidemiology and Importance

CVA accounts for 24-29% of chronic cough cases in adult nonsmokers, making it one of the most common causes of chronic cough. 1 The American College of Chest Physicians emphasizes that asthma should always be considered as a potential etiology in any patient with chronic cough (Grade A recommendation). 1

Pathophysiology

CVA shares key pathologic features with typical asthma, including:

• Eosinophilic airway inflammation present in sputum, bronchial mucosa, and bronchoalveolar lavage fluid 1, 2
• Airway smooth muscle infiltration by mast cells 1
• Subepithelial layer thickening, indicating airway remodeling 1
• Bronchial hyperresponsiveness demonstrable by methacholine challenge testing 1

Diagnostic Approach

The diagnosis of CVA requires a systematic approach because routine testing may be normal:

Bronchial Challenge Testing

• Methacholine inhalation challenge testing should be performed to demonstrate bronchial hyperresponsiveness when physical examination and spirometry are non-diagnostic. 1
• A positive methacholine test is consistent with but not diagnostic of CVA. 1
• A negative methacholine test essentially excludes CVA due to its very high negative predictive power. 1

Inflammatory Markers

• Non-invasive inflammatory markers such as sputum eosinophil counts and fractional exhaled nitric oxide (FeNO) can provide additional evidence supporting the need for corticosteroid treatment. 1

Therapeutic Diagnosis

• The definitive diagnosis of CVA can only be made after documented resolution of cough with specific antiasthmatic therapy. 1

Clinical Course and Prognosis

CVA may present in several patterns:

• Isolated cough may serve as a precursor to typical asthmatic symptoms developing later 1
• Approximately 30% of CVA patients develop typical bronchial asthma within several years 2
• In some patients, cough remains the predominant or sole symptom indefinitely 1

Key Clinical Pitfalls

Clinicians must maintain high clinical suspicion because:

• CVA is frequently overlooked or misdiagnosed due to the absence of typical asthmatic symptoms 1, 3
• Patients may suffer for prolonged periods (ranging from 2 months to 20 years) before correct diagnosis 3, 4
• The severity of cough can significantly impact quality of life, causing interference with sleep, work, social activities, and even urinary or fecal incontinence 3, 4