Letter: it is time to adopt new objective parameters to accurately identify patients with functional heartburn

Dear Editors, We read with great interest the study by Choksi et al (1) showing that symptom association probability (SAP) is not a useful parameter to distinguish functional heartburn (FH) from reflux hypersensitivity (RH), when analyzing acid measurements obtained by means of wireless pH monitoring for 48 hours. In particular, this traditional index of symptom-reflux association resulted to be highly variable between day 1 and day 2 of pH testing, thus leading to different diagnosis of hypersensitive or functional esophagus for each monitored day and, moreover, pre-operative SAP values were not able to predict surgical outcome. This study is a further confirmation of the well known limited diagnostic accuracy of this parameter (2,3), particularly when measurement of all types of reflux is not performed (i.e. pH-metry instead of impedance-pH), and of the need of having new and more objective features to improve our ability to identify patients with RH and FH. In keeping with this requirement, some recent investigations have highligthed the relevance of some innovative, objective and reliable parameters that can be adopted when applied to tracings achieved with impedance-pH monitoring, which at present is recognized as the best technique to detect gastroesophageal reflux episodes (4). They are represented by the baseline impedance, especially when measured at night when swallow or reflux-related artifacts are minimal (mean nocturnal baseline impedance = MNBI), which has been shown to be a marker of impaired mucosal integrity, and the post-reflux swallow-induced peristaltic wave (PSPW), defined by an antegrade impedance-detected bolus propagation reaching all distal impedance monitoring sites within 30s of a reflux episode, which has been highlighted as a marker of chemical clearance and an hallmark of GERD pathogenesis (5-7). The PSPW index and MNBI have been shown to provide significant diagnostic yield in distinguishing RH from FH, even though SAP was negative (8,9). More importantly, it has been demonstrated at ROC analysis (10) that the combined assessment of PSPW and MNBI allowed excellent separation of RH and FH (AUC 0.957), in that SAP positivity was only found in 62% of hypersensitive patients, whereas PSPW/MNBI positivity was detected in 92% of them (p<0.0001). Therefore, the calculation of PSPW index and MNBI affords the diagnosis of RH independently of and significantly better than SAP index. In other words, the impairment of chemical clearance, as expressed by a low PSPW index and the loss of mucosal integrity, as expressed by a low MNBI, provide a potential explanation of the increased perception of reflux episodes in patients with RH. In addition, it is worth noting that these two new indices have the great advantage to provide an objective measurement and therefore do not suffer from patients’ symptom reporting or from the lack of reflux episodes occurrence during the monitoring day. So, we believe that the analysis of PSPW and MNBI become part of the standard assessment of impedance-pH tracings in order to improve the distinction between hypersensitive and functional esophagus in the so commonly seen patients with endoscopy-negative heartburn.