Cough variant asthma (CVA) is a specific form of asthma defined by a persistent cough as the primary, and often only, symptom. CVA is a unique manifestation of the underlying airway inflammation and hyperresponsiveness characteristic of asthma. Unlike the classic presentation, CVA frequently goes unrecognized because it lacks the commonly associated respiratory distress symptoms.
How CVA Differs from Classic Asthma
The fundamental difference between CVA and classic asthma lies in the expression of bronchial hyperresponsiveness. Classic asthma is identified by a triad of symptoms: wheezing, shortness of breath, and chest tightness. In contrast, CVA isolates the cough, presenting a diagnostic challenge for clinicians. The inflammatory processes within the airways are similar to those in classic asthma, involving heightened sensitivity of the bronchial tubes.
This increased sensitivity, or airway hyperresponsiveness, causes the airways to constrict easily in response to various triggers. In CVA, this constriction is insufficient to cause the audible wheeze or significant airflow obstruction seen in classic asthma. Spirometry, a common lung function test, is often normal in CVA patients, distinguishing it from the classic form where reduced airflow is typical. CVA is still considered a full variant of asthma because it shares the same underlying pathology and responds to the same anti-inflammatory treatments.
Characteristics of the CVA Cough
The cough associated with CVA possesses specific qualities that help distinguish it from other causes of chronic coughing. It is typically dry and non-productive, meaning it does not bring up mucus. This persistent cough is classified as chronic, lasting for more than eight weeks in adults and four weeks in children. The repetitive nature of the cough can be severely disruptive, often leading to exhaustion, sleep interruption, and lightheadedness.
The cough frequently worsens at night or in the early morning upon waking. Common triggers provoke coughing episodes, including physical activity, exposure to cold air, and strong odors or irritants. The cough can also begin following a viral upper respiratory infection, persisting long after the initial illness has resolved. This pattern of chronic, dry coughing strongly suggests CVA.
Confirming the Diagnosis
Diagnosing CVA requires a methodical approach, beginning with the exclusion of other common causes of a chronic cough, such as postnasal drip, gastroesophageal reflux disease (GERD), or medication side effects. Standard spirometry is usually performed first, but the results often fall within the normal range for CVA patients, indicating no baseline obstruction of airflow. A specialized test is then required to reveal the hidden airway sensitivity.
The definitive diagnostic tool for CVA is the Methacholine Challenge Test, also known as a bronchial provocation test. This procedure involves inhaling increasing concentrations of methacholine, a substance that causes temporary airway constriction in sensitive lungs. Lung function is measured after each dose. A positive result is defined as a drop of 20% or more in the Forced Expiratory Volume in one second (\(\text{FEV}_1\)). This test is highly sensitive for detecting the airway hyperresponsiveness that characterizes CVA.
Treatment and Managing Progression
The treatment regimen for CVA mirrors that of classic asthma, focusing on reducing underlying airway inflammation. Inhaled corticosteroids (ICS) are the primary intervention, used daily to control chronic inflammation in the bronchial tubes. These medications soothe the hypersensitive airways, reducing the frequency and severity of the cough. Short-acting bronchodilators may also be prescribed as a rescue medication to quickly relax airway muscles during an acute coughing episode.
Management of CVA is important because the condition carries a risk of progression into classic asthma if left untreated. Studies suggest that 30% to 40% of adults with untreated CVA may eventually develop the full range of classic asthma symptoms, including wheezing and shortness of breath. Consistent use of inhaled corticosteroids and avoidance of known triggers significantly lowers this risk. With appropriate treatment, the chronic cough can be effectively managed, and progression to classic asthma is often preventable.