The most appropriate treatment is to add a proton pump inhibitor to this patient's current asthma treatment regimen. Although she has a clear diagnosis of asthma (based on her methacholine challenge testing results) and her cough has partially responded to asthma therapy, she continues to have symptoms and has additional clinical findings consistent with gastroesophageal reflux disease (GERD) as a potential cause of her persistent cough symptoms. Respiratory symptoms associated with GERD are common, and reflux is frequently a cause of chronic cough. GERD is also extremely common in patients with asthma, with some estimates suggesting some degree of reflux in as many as 90% of patients. GERD can make underlying asthma worse through direct reflux of acidic gastric contents into the respiratory system, resulting in upper airway inflammation or direct airway injury. The reflux of gastric contents into the lower part of the esophagus can also cause reflex bronchoconstriction. There is evidence that treating GERD in patients with asthma improves asthma control. In most patients with asthma and suboptimal control of symptoms, a history consistent with GERD is adequate to justify a trial of empiric antacid therapy without further testing for evidence of reflux. There is no evidence, however, that treating all patients with asthma but without symptoms consistent with GERD is of benefit.
In the setting of asthma treatment, it is necessary to control for confounders such as GERD before escalating the intensity of asthma therapy, such as adding a long-acting β2-agonist. Stepping up asthma treatment in this patient would be appropriate in the absence of a possible diagnosis of GERD or if her symptoms do not respond to antacid therapy.
Repeating a methacholine challenge test is not indicated if the initial study was adequate for diagnosing asthma and the patient has had a response to treatment. In addition, bronchoprovocation studies carry some risk, making it inappropriate to repeat the study without a clear indication.
Antitussives are frequently used in treating acute cough and may be helpful in patients with chronic cough refractory to other therapies, based on the underlying cause. Treatment with antitussive therapy in this patient with cough-variant asthma and possible comorbid GERD would not be appropriate without further assessing control of these underlying issues.