Chronic Cough Due to Gastroesophageal Reflux Disease: GERD
A post hoc analysis of the data revealed that observing few or no lipid-laden alveolar macrophages might be helpful in ruling out aspiration as the cause of the parenchymal lung disease. This conclusion was reached on the basis of the following information: a lipid cellular index of > 100, which was computed by multiplying the observed amount of intracellular lipid in 100 cells, graded from 0 to 4, had a specificity of 57%, and sensitivity and negative predictive values of 100%. In the second study, while it was found that the presence of an increased number of lipid-laden macrophages in induced sputum predicted the presence of oropharyngeal reflux by dual-channel 24-h esophageal and pharyngeal pH monitoring, it was not determined that these same patients actually had aspirated. Most relevant to the discussion in this section, the diagnostic usefulness of the presence of lipidladen macrophages in induced sputum was not assessed in patients with chronic cough. On the basis of these studies, assessing for lipid-laden macrophages in BAL fluid and induced sputum does not appear, at this time, to have a role to play in diagnosing cough due to GERD. so
Because inhaled tussigenic challenges with capsaicin have revealed the increased sensitivity of the cough reflex in a variety of diseases (eg, asthma, viral upper respiratory tract infections, and angiotensin-converting enzyme inhibitors) in addition to GERD and even in patients with GERD without cough, inhaled tussigenic challenges with capsaicin at this time do not appear to have a role to play in diagnosing cough due to GERD. Because exhaled nitric oxide can be a marker of airway inflammation in patients with asthma, its measurement may be of potential benefit in diagnosing the cause of chronic cough. However, preliminary studies to date have not shown exhaled nitric oxide measurements to be particularly helpful in diagnosing cough due to GERD. In a cross-sectional prospective study utilizing exhaled nitric oxide as well as induced sputum, it was determined that GERD, when associated with cough or mildly symptomatic asthma, did not cause or aggravate existing airway inflammation as measured by exhaled nitric oxide or other indexes of airway inflammation (eg, cell counts and fibrinogen level). Because two prospective studies in subjects with chronic cough due to GERD have produced divergent results during intraesophageal infusions of hydrochloric acid to provoke cough, a negative Bernstein test cannot be used to exclude the diagnosis of cough due to GERD. While a radioisotope scintiscan that documents pulmonary aspiration of gastric contents is definitive, it is not routinely performed because it may be positive in not > 50% of subjects with suspected aspiration, and it has a much lower sensitivity.