This observational study aimed at comparing esophageal mucosal integrity in different subtypes of refractory GERD patients, including mild and severe EE, NERD and BE patients, as well as investigating the impact of abnormal anti-reflux barrier and esophageal body dysmotility on the mucosal integrity for the first time. Compared with FH patients, significantly decreased MNBI values were found in refractory EE, NERD and BE patients. However, the severity of macroscopic mucosal changes was not consistent with the degree of microscopic impairments reflected by baseline impedance in the distal esophagus. Furthermore, weakened esophageal body peristalsis, type III EGJ, and shortened LES were the risk factors for the impaired mucosal integrity in EE, NERD, and BE patients, respectively. We therefore conclude that HREM and MII-pH parameters were of great value in the identification and prediction of esophageal mucosal impairments in refractory GERD patients.
DIS and reduced transepithelial resistance (TEER) could morphologically and functionally distinguish the impaired mucosal integrity in GERD patients [30–32]. Earlier in an acid perfusion experiment, BI values decreased along with DIS and correlated with esophageal TEER positively [15]. Furthermore, BI values were found to be lower in patients with pathological acid exposure than in patients with physiological acid exposure, and both were lower than in healthy people [16]. Subsequently, BI was proposed an indicator of esophageal microscopic abnormalities caused by reflux and a marker of reflux burden [14–16, 33]. FH refers to a burning sensation in the substernal region without endoscopic injury, abnormal acid exposure, and correlation between reflux events and symptoms [19]. The severity of histological impairments and the level of BI values in FH patients were comparable to those in healthy people [17, 20, 21], thus they were used as control in this study.
Decreased MNBI values to varying degrees were discovered in all groups of refractory GERD in our study. MNBI values of EE patients and NERD patients ranged from differences to no difference in previous studies [34–36]. No discrepancy in MNBI values between EE (both LA-A/B and LA-C/D) and NERD patients was found here, signifying a microscopic mucosal injury in NERD patients although no macroscopic mucosal injury at routine endoscopy. This was supported by the fact that DIS existed in NERD patients [15]. In addition, MNBI values were lower in BE patients than in control subjects, in accordance with Hemmink’s research [37]. This result suggested that the esophageal region beyond Barrett’s mucosa was also likely to be impaired, as MNBI was measured above Barrett’s mucosa. Further research is needed to confirm the observation.
The diagnostic criteria for IEM in CCv4.0 is more strict than in CCv3.0, which contains larger proportions of ineffective or failed swallows, and fragmented peristalsis is also included in IEM in CCv4.0. In Reddy’s study, the number of total reflux events (22.7% vs 9.0%, P < 0.01) and the bolus exposure time (3.4% vs 2.1%, P < 0.01) in GERD patients with more than 50% ineffective swallows were much more than those with normal motility. In addition, the total reflux events and AET increased with the increased proportion of ineffective swallows [38]. Rengarajan et al. reported that more severe dysmotility such as absent contractility was associated with abnormal reflux burden more than less severe dysmotility such as IEM [39]. The incidence of esophageal mucosal impairments increased with the increasement of reflux burden. In an HREM test of GERD patients undergoing 10 swallows, abnormal MNBI was related to > 70% ineffective swallows (P = 0.046), tended to be related to > 70% fragmented swallows (P = 0.076) and was unrelated to ≥ 50% failed swallows (P = 0.580) [40]. Our results showed that IEM and absent contractility were the risk factor for mucosal impairments in mild and severe refractory EE patients, respectively. A decreased MNBI value was the result of abnormal reflux burden, esophageal body dysmotility and reflux clearance obstacles [29, 41, 42].
The structure and function of EGJ play an essential role in the anti-reflux barrier, and the primary mechanism is the high-pressure band between LES and CD, preventing the occurrence of reflux. It is believed that reflux burden increases with the separation between LES and CD, and the pathological morphology of EGJ (a hiatus hernia) is a predictor of abnormal acid exposure [39, 43, 44]. Consequently, it was not surprising that decreased MNBI was related with type III EGJ in NERD patients here. EGJ-CI was a new indicator of EGJ contractility and it decreased with the upgrade of EGJ morphology, EGJ contractility gradually weakened with the increase of the gap between LES and CD [25, 43]. EGJ-CI could not predict MNBI in Rogers’ study but was able to predict AET in Rengarajan’s study [39, 40, 44]. Our data showed that EGJ-CI was associated with MNBI at 3cm above LES in LA-C/D patients only in univariate analysis, not in multivariate analysis. We concluded that EGJ-CI has a definite influence on mucosal integrity but not as significant as EGJ morphology.
Reflux usually occurs via different mechanisms based on the anatomical and physiological variation of EGJ and LES, such as low LES pressure and transient LES relaxations [41]. Decreased LES resting pressure has been reported to be a predictor of increased acid exposure [38, 45]. IRP reflects the relaxation function of LES. Neither LES resting pressure nor IRP was significantly related to MNBI values in our study. However, we found that the decreased LES length led to decreased MNBI values in BE patients, supported by the views that shortened esophagus was related to more reflux events and higher DeMeester score [46, 47].
Limitations could not be avoided and impeded the reliability of our research, the predominant of which may be the limited sample size, but a certain number of subjects were required in regression analysis. All refractory GERD patients were recruited from only one hospital, which may lead to potential selection biases. The prevalence of BE is low and most are short-segment BE in Asia area, and thus the application of Seattle protocol is limited [48]. Only 2 biopsy samples were obtained from each patient in our study and the diagnosis of BE was likely to be inaccurate. Moreover, instead of healthy people, FH patients, whose MNBI level was comparable to healthy people, were used as a control group. Even so, our findings still had values in evaluating the characteristic of mucosal integrity impairments and in improving the therapeutic strategy for refractory GERD.