Cough variant asthma (CVA) has been identified as a precursor of asthma or a pre-asthmatic state due to the slightly heightened bronchial responsiveness and effectiveness of bronchodilator therapy. However, the accumulating evidence has indicated that the pathophysiology is diverse between CVA and bronchial asthma. The most common fundamental physiologic feature is a heightened cough response to methacholine-induced bronchoconstriction particularly in CVA, whereas this response is reduced in bronchial asthma.

The sensitivity of cough receptors that is located in the superficial layer of the airway wall is normal in CVA and bronchial asthma, but it is heightened in atopic cough. The pathologic feature observed in CVA is eosinophilic inflammation of the central to peripheral airway, which is reflected by eosinophilia in induced sputum, biopsy done in bronchial mucosa, and bronchoalveolar lavage fluid. The diagnosis of CVA is commonly based on therapeutic diagnostic procedures, whereas the pathophysiologic diagnosis is ideal. The reason behind this is that measurements of the sensitivity of cough receptors to the inhaled capsaicin and the cough response to the induced bronchoconstriction are not possible in many chest clinics across the world.

The effectiveness of a beta2-agonist for a patients coughing is assessed to make a diagnosis of CVA. When the bronchodilator treatment is judged as effective, an uncertain diagnosis of CVA is made. At that time, induction therapy was started for resolution of the cough. The induction therapy includes of beta2-agonists, inhaled corticosteroids and leukotriene receptor antagonists. In few patients in whom the cough does not subside with the induction therapy, then the short-burst oral corticosteroids (1-3 weeks) can be added. If the cough still does not diminish with this treatment, then the patient should be referred to cough specialists. Also, when the cough subsides with the induction therapy, long-term management using inhaled corticosteroids is recommended, as 30% of patients might develop typical bronchial asthma in several years. Difficulties faced with the therapeutic diagnosis are spontaneous relief of cough giving a false positive result and resistance to the induction therapy, resulting in a false-negative result. Therefore, a pathophysiologic diagnostic procedure should be established in the coming future.

Source: Fujimura M. [Pathophysiology, diagnosis and treatment of cough variant asthma]. Rinsho Byori. 2014 May;62(5):464-70. Japanese. PMID: 25051661.