Chronic Cough Due to Gastroesophageal Reflux Disease: Methods
The standard, catheter-based 24-h esophageal pH-monitoring study has its own inherent limitations. For example, because it cannot detect reflux events with a pH similar to that of the normal esophagus, the monitoring study can be entirely normal at a time when nonacid GERD is the cause of cough. In this situation, barium esophagography may be the only available test to reveal GER of potential pathologic significance (see the discussion below regarding esophageal impedance monitoring). Barium esopha-gography has revealed reflux to the mid-esophagus or higher when refluxate from the stomach had a pH value similar to that of the normal esophagus. Because the majority of patients with cough due to GERD do not have esophagitis or Barrett epitheli-um, a normal esophagoscopy finding does not rule out GERD as the cause of cough. While pilot studies have shown that ambulatory esophageal pH monitoring using a wireless recording system is a viable option for patients who are unwilling or unable to undergo conventional ambulatory pH-monitoring studies using a transnasally positioned pH catheter, it is likely that future studies will show that the wireless system will have the same limitations as the standard catheter-based systems, which were summarized above. read more
Because 24-h esophageal pH monitoring in the context of prospectively evaluating chronic cough has a sensitivity of < 100% (approximately 90%) and its specificity has ranged between 66% and 100%,>> even when interpreted according to the guidelines described above, and because these ranges have been confirmed in a retrospective study, it is recommended that treatment be initially started in lieu of testing for patients who fit the clinical profile for cough due to GERD (Table 1). This recommendation is supported by a retrospective, before-and-after intervention study in which GERD was diagnosed as the cause of chronic cough in 79% of patients (44 of 56 patients) by the empiric trial of therapy, thus obviating the need to perform 24-h esophageal pH monitoring. The performance of 24-h esophageal pH monitoring is recommended during therapy when cough does not improve or resolve to assist in determining whether the therapy needs to be intensified or medical therapy has failed. The usefulness of this recommendation was shown in a small prospective before-and-after intervention trial. Hopefully, in the near future, it will be determined whether simultaneous 24-h monitoring of intraesophageal impedance and pH will allow us to more easily determine when acid reflux disease and/or nonacid reflux disease are the causes of chronic cough.