Acidic Pharyngeal Reflux Does Not Correlate with Symptoms and Laryngeal Injury Attributed to Laryngopharyngeal Reflux

Abstract

Background

Laryngopharyngeal reflux (LPR) is suspected when the symptoms are attributed to the penetration of acidic gastroesophageal reflux (GER) into the larynx. However, the relationships between the intensity of LPR and symptoms and laryngeal injury have not been elucidated. Several factors confound the study of LPR, namely pH is monitored in the pharynx (pharyngeal reflux) but the pharyngeal acidity (pH) required to induce laryngeal injury is unknown, the GER origin of pharyngeal acid is not always established, and a recent treatment with proton pump inhibitors (PPI) confounds the analysis.

Aims

We aimed to limit these confounding factors to analyze the relationship between LPR and symptoms and laryngeal injury.

Methods

We used dual pharyngeal and distal esophageal 24-h pH/impedance monitoring to establish GER origin of pharyngeal reflux, we used an unbiased approach to analysis by evaluating a whole range of acidity (pH < 6, pH < 5.5, pH < 5.0, pH < 4.5 and pH < 4.0) in patients with suspected LPR without PPI for > 30 days.

Results

Pharyngeal reflux was (median[IQR]) 14[8–20.5] and 4[1.5–6.5] pharyngeal reflux episodes with pH < 6.0 and pH < 5.5, respectively. Pharyngeal reflux with pH < 5.0 was rare. Comprehensive analysis did not reveal any correlation between symptoms (reflux symptom index) or laryngeal injury (reflux finding score) and the number of pharyngeal reflux episodes or duration of pharyngeal acid exposure at any pH level.

Conclusion

Unbiased comprehensive approach did not reveal any relationship between acidic pharyngeal reflux and the symptoms or laryngeal injury attributed to LPR. Limited clinical usefulness of pharyngeal monitoring reported by others is unlikely due to confounding factors.

Introduction

The term laryngopharyngeal reflux (LPR) is used when the patient’s symptoms and laryngeal injury are attributed to gastroesophageal reflux content penetrating into the larynx. Recent advances in esophageal monitoring technologies provided important insights into LPR [1–11]. However, the relationship between the intensity of laryngopharyngeal reflux and symptoms and laryngeal injury attributed to laryngopharyngeal reflux has not been elucidated.

Because the acid is the major corrosive component of gastroesophageal reflux (GER), arguably, the most straightforward hypothesis is that symptoms and laryngeal injury attributed to laryngopharyngeal reflux are directly related to acidic GER penetrating into the larynx. This hypothesis predicts a correlation between the amount of acidic reflux to the larynx and the symptoms and laryngeal injury. However, there are several important conceptual, technical and logistic hurdles that are impeding the study of acidic laryngopharyngeal reflux. In this study, we will evaluate our hypothesis while addressing these hurdles.

Firstly, because it is difficult to reliably monitor pH in the larynx which contains air [12–14], the acidic laryngopharyngeal reflux is inferred from the pH monitoring in the pharynx above the upper esophageal sphincter (UES) (often termed hypopharynx) [15]. However, it is unknown how much of the acid detected in the pharynx penetrates into the larynx, and how much acid in the larynx is needed to induce laryngeal injury (for example, very little acid around pH = 6.0 can induce an injury of respiratory epithelium and activate airway sensory nerves [16]). Therefore, an analysis of broad range of acidity (pH) and other quantitative parameters of reflux into pharynx (pharyngeal reflux) is required.

Secondly, from the pharyngeal pH monitoring alone, it cannot be determined if an observed decrease in pharyngeal pH is caused by GER from the esophagus. Therefore, a simultaneous monitoring of gastroesophageal reflux is required. Finally, PPI treatment confounds the study of LPR pathophysiology inasmuch as such treatment can exert a long-term influence on pathogenesis of the symptoms and laryngeal injury [17]. However, a widespread use of PPI makes it difficult to enroll patients who do not currently receive PPI treatment. Therefore, active logistic strategies to enroll such patients are required.

We have largely overcome these hurdles in the present study. We enrolled patients that were at least 30 days without PPI treatment. We used dual pharyngeal and distal esophageal 24-h pH/impedance monitoring and selected appropriately sized pH/impedance catheter based on manometrically determined UES and lower esophageal sphincter (LES) to reliably monitor GER reaching the pharynx. We then performed a comprehensive quantitative analysis of pH, number and duration of pharyngeal reflux episodes. Our data indicate that a simple direct relationship between pharyngeal reflux and symptoms or laryngeal injury attributable to laryngopharyngeal reflux is unlikely.

Patients and Methods

The protocol of the study was approved by the decision of the Ethical Committee of Jessenius Faculty of Medicine, Comenius University with the number EK 1485/2014. This was a prospective single-center study. The evaluation was performed on an outpatient basis. Consecutive patients referred for suspected LPR to Gastroenterology Clinic, Jessenius Faculty of Medicine, between November 2014 and May 2016 were prospectively screened for eligibility. A careful interview was conducted to assess the symptoms suggestive of LPR and personal history was obtained. Inclusion criteria were laryngopharyngeal symptoms such as cough, hoarseness, globus, and throat clearing for > 6 months. Exclusion criteria were age below 18 years old, infection of the upper or lower airways in the previous month, smoking, alcohol consumption > 40 g/d, history of thoracic or abdominal surgery, pregnancy or breastfeeding, neurological disorders, active malignancy, inflammatory bowel disease, and the presence of gastric inlet patch in the esophagus on the upper endoscopy. Written informed consent was obtained from each eligible subject who agreed to be enrolled into the study. Thirty-five subjects that met initial inclusion criteria were evaluated. These subjects were instructed to withhold PPI therapy for 30 days. After this period, the subjects completed reflux symptom index (RSI) [18] questionnaire (Table 1), underwent high-resolution manometry (HRM), dual pharyngeal and esophageal 24-h pH/impedance monitoring (as described in detail below), and flexible laryngoscopy at which the reflux finding score (RFS) [19] was obtained. Only the subjects that had positive reflux symptom index (RSI > 13) or reflux finding score (RFS > 7) and at least one LPR episode on dual 24-h pH/impedance monitoring (as defined below) were included. Of 35 evaluated subjects 27 patients met these criteria and were included in the analysis. The remaining patients had RSI ≤ 13 AND RFS ≤ 7 (N = 2) or had no LPR episode on dual 24-h pH/impedance monitoring (N = 5) or experienced technical issues during 24-h pH/impedance measurement that made an evaluation of the recording impossible (N = 1) and were excluded from the analysis.

Table 1.

The reflux symptom index questionnaire developed by Belafsky et al. is a validated self-administered nine-item instrument for LPR that documents symptom severity in LPR

Within the past month, how did the following problems affect you?
1. Hoarseness or a problem with your voice	0	1	2	3	4	5
2. Clearing your throat	0	1	2	3	4	5
3. Excess throat mucous or postnasal drip	0	1	2	3	4	5
4. Difficulty swallowing food, liquids or pills	0	1	2	3	4	5
5. Coughing after you ate or after lying down	0	1	2	3	4	5
6. Breathing difficulties or choking episodes	0	1	2	3	4	5
7. Troublesome or annoying cough	0	1	2	3	4	5
8. Sensations or something sticking in your throat	0	1	2	3	4	5
9. Heartburn, chest pain, indigestion, or stomach acid coming up	0	1	2	3	4	5

HRM and dual pharyngeal and esophageal 24-h pH/impedance monitoring were performed after overnight fast. We used ManoScan^™ ESO high-resolution manometry system (given imaging). UES and LES were located. Dual pharyngeal and esophageal 24-h pH/impedance monitoring was performed with pH/impedance catheters VersaFlex^™ with two pH sensors and eight impedance electrodes (given imaging). Three sizes of catheters with the distance of 15 cm, 19 cm, and 22 cm between pH sensors were available for the study. In catheters with pH sensors distance 19 and 22 cm, impedance electrodes were 1 cm above and 1 and 3 cm below the distal pH sensor, 1 cm above and 2, 5, and 7 cm below the proximal pH sensor (Fig. 1a). In catheters with pH sensors distance 15 cm, impedance electrodes were 1 and 3 cm below and 1, 3, and 5 cm above the distal pH sensor and 1 and 3 cm below and 1 cm above the proximal pH sensor. Before recording, the catheters were calibrated using pH 4.0 and 7.0 buffer solutions. The appropriate catheter size was selected according to the locations of the UES and LES determined by HRM so that when the catheter was placed transnasally the proximal pH sensor was approximately 1 cm above the proximal margin of the UES and the distal pH sensor was approximately 5 cm above the proximal margin of the LES. If this was not possible to achieve, the catheter of the smaller diameter between the pH sensors was selected and placed according to the UES location. The average position of the distal pH sensor was 5.5 ± 0.1 cm above the proximal margin of the LES (i.e., in most patients, the distal probe was positioned between 5 and 6 cm above the proximal margin of the LES). Patients were encouraged to maintain their normal activities, sleep schedule, and eat their usual meals during the 24-h monitoring. We used Digitrapper^™ pH-Z Testing System for the 24-h recording. Patients were also asked to mark the time of eating and the horizontal body position on the data recorder.

Fig. 1.

Recording of pharyngeal reflux. a Representative example of a dual pH sensor catheter placing. The pH sensors were located 1 cm above the UES and 5 cm above the LES. Impedance electrodes are located 1 cm above and 2, 5, and 7 cm below the proximal pH sensor and 1 cm above and 1 and 3 cm below the distal pH sensor. b Representative trace of pharyngeal acidic reflux episode recorded by dual pharyngeal and distal esophageal pH/impedance. Sudden drop of pH and impedance in the distal esophagus (black arrow, GER) is followed by distal to proximal decrease in impedance (distal to proximal movement of the refluxate) and subsequent drop of pH in the pharyngeal pH sensor (red arrow, LPR)

Tracings were visually analyzed using AccuView pH-Z version 5.2 software (given imaging). One blinded observer was responsible for the evaluation of pH/impedance studies. Meals were excluded from the analysis. Gastroesophageal reflux events by impedance changes were defined on the basis of previous human studies [20, 21]. Liquid gastroesophageal reflux was defined as a retrograde 50% drop in impedance starting distally and propagating to at least the next two more proximal measuring segments. Gas gastroesophageal reflux was defined as simultaneous increase in impedance above 5000 Ω starting in the most distal impedance channels and propagating to at least the next two more proximal impedance measuring segments. Mixed gastroesophageal reflux (liquid–gas) was defined as gas reflux occurring simultaneously before or during a liquid reflux.

Consistent with the studies in the field, we used the pharyngeal reflux as a surrogate of laryngopharyngeal reflux [2, 7, 9, 22–24]. Pharyngeal reflux was identified when a gastroesophageal reflux episode (as defined above) was temporarily associated with a drop of pH in the proximal pH sensor (Fig. 1b). Special effort was dedicated to exclude pH changes in the proximal pH sensor due to swallowing, sensor drying, and other artifacts based on their know pH/impedance patterns. We based our analysis on the assumption that in the absence of swallows a sudden drop of pH in the hypopharynx occurring in a close temporal sequence with a preceding reflux detected by distal pH/impedance is a pharyngeal reflux event. In order to allow for comprehensive analysis of LPR, we performed a separate analysis for proximal pH≤6, 5.5, 5, 4.5, and 4. If pH in the proximal sensor was already lower before the reflux event, the reflux was considered as pharyngeal reflux when pH drop of at least 0.5 unit was observed during the reflux. Pharyngeal reflux was quantified as the number of pharyngeal reflux events for each pH. The pharyngeal acid exposure time for each pH was calculated as the cumulative time of pH ≤ 6, 5.5, 5, 4.5, and 4. For example, the duration of pharyngeal acid (pH < 5.0) exposure calculated as cumulative time pH of pharyngeal reflux was pH < 5.0 during 24 h.

In addition, tracings were also reviewed for the number of pharyngeal reflux according to the criteria developed previously. According to Zerbib et al. [7], LPR was defined as a retrograde 50% impedance drop, both distally and proximally, within the entire esophagus if no swallow occurred during the pharyngeal impedance drop. According to Kawamura and coworkers, pharyngeal reflux events were defined analogously to gastroesophageal reflux events. A liquid reflux event was defined as an impedance drop of at least 50% from baseline and below 1200 Ω preceded by or simultaneous with an esophageal liquid reflux event [25]. The esophageal acid exposure time and DeMeester score were automatically calculated by the analysis software. Furthermore, the number of all reflux events, number of liquid, gas and mixed reflux events and number of acidic and weakly acidic reflux events were obtained.

Statistical analysis.

The number of reflux episodes is expressed as median and interquartile range (IQR). The duration of reflux episodes is expressed as mean ± SEM. The strength of a linear association between the analyzed variables was measured by the Pearson correlation coefficient (r). Online calculator http://www.socscistatistics.com/tests/pearson/ was used. P was calculated based on r and N using online application http://www.socscistatistics.com/pvalues/pearsondistribution.aspx. P < 0.05 was considered significant.

Results

Characterization of Pharyngeal Reflux in Patients with Suspected LPR Based on Symptoms and Signs

Twenty-seven patients (20M/7F) completed the study with an average age of 48.1 ± 2.5 years. Because of the proximal pH sensor position in the pharynx, we denote here the reflux detected by this sensor strictly as pharyngeal reflux. We determined the number of pharyngeal acidic reflux episodes during 24-h recording (Fig. 2a). For each pharyngeal acidic reflux episode, we determined the maximum drop of pH at 0.5 intervals as follows: pH < 6.0, pH < 5.5, pH < 5.0, pH < 4.5, and pH < 4.0 and the duration of pharyngeal acid exposure calculated as cumulative time during which the pH of pharyngeal reflux was below each pH level during 24 h (Fig. 2b). Our data (Fig. 2) show that pharyngeal reflux with pH < 5.0 was relatively rare, both in the terms of the number of pharyngeal acidic reflux episodes and the duration of acidic pharyngeal exposure (pH < 5.0). There was slightly more pharyngeal acidic reflux with pH = 5.0–5.5, but by far the most common acidic pharyngeal reflux was the reflux with pH = 5.5–6.0.

Fig. 2.

Quantification of pharyngeal acidic reflux in patients diagnosed with LPR. a Number of pharyngeal acidic reflux episodes with indicated acidity during 24 h. b Duration of pharyngeal acid exposure calculated as cumulative time pH of pharyngeal reflux was below indicated pH during 24 h. N = 27

For comparison, we also quantified pharyngeal reflux by using impedance-based criteria previously applied to dual pharyngeal and esophageal 24-h pH/impedance monitoring [7, 25, 26]. According to the criteria developed by Zerbib et al. [7], there were 0.5[1–3] LPR episodes of which 1[0–2.5] and 0[0–0] were in upright and supine position, respectively. Of the total of 51 impedance refluxes occurring in the supine position, the proportion reaching the minimum pH = 6.0, pH = 5.5, pH = 5.0, pH = 4.5, and pH = <4.0 was 49% (25/51), 27% (14/51), 6% (3/51), 0% (0/51), and 18% (9/51), respectively. Only six impedance refluxes occurred in the supine position, and the pH the majority of them had pH ≥ 5. According to criteria developed by Kawamura et al. [25], there were 0[0–1] LPR episodes detected in nearly all patients in an upright position.

Relationship Between Pharyngeal Reflux and Distal Gastroesophageal Reflux

The number of distal esophageal (gastroesophageal) reflux episodes was 40[31.5–52.5]. The majority 33[16.5–40] of distal esophageal reflux episodes were liquid reflux episodes, 9[5–11.5] were mixed liquid/gaseous reflux episodes, and 3[1.5–5] were gaseous reflux episodes. Approximately two-thirds 26[15–39] of distal esophageal reflux episodes were acidic (pH < 4) reflux episodes, while most of the remaining episodes were weakly acidic reflux episodes. The distal esophageal acid (pH < 4) exposure time (AET) was 2.9 ± 0.5%, and DeMeester score was 12.3 ± 1.8.

Because pharyngeal reflux is a proximal extension of distal esophageal reflux, we evaluated the correlation between pharyngeal and distal esophageal reflux. There was a weak but significant positive correlation between the number of pharyngeal acidic (pH < 6.0) reflux episodes and distal esophageal (gastroesophageal) acidic (pH < 4.0) reflux episodes (Fig. 3a). There was also a weak but significant positive correlation between the duration of pharyngeal acid (pH < 6.0) exposure and distal esophageal acid exposure time (AET, % of time distal esophageal pH < 4.0) (Fig. 3b). This correlation was also observed for more acidic (pH < 5) pharyngeal reflux (r = 0.39, N = 27, P < 0.05). These data indicate that more distal esophageal acid exposure translates into more pharyngeal acid exposure, although the relationship is not very strong. Not surprisingly, because the pharyngeal acidic (pH < 4.0) reflux episodes were very rare, there was no correlation between pharyngeal acid (pH < 4) exposure time and distal AET (r = 0.27, N = 27, P = NS).

Fig. 3.

Pharyngeal acidic reflux correlates with distal esophageal acidic reflux in patients diagnosed with LPR. **P < 0.01. a Correlation between the number of pharyngeal acidic (pH < 6.0) reflux episodes and distal esophageal acidic (pH < 4.0) reflux episodes. b Correlation between the duration of pharyngeal acidic (pH < 6.0) exposure and distal esophageal acid (pH < 4.0) exposure time

Based on DeMeester score > 14.72, the pathological GER was observed in 10 of 27 patients. We reasoned that the correlation between pharyngeal reflux and distal reflux may be stronger in patients with pathological GER simply because they have more distal esophageal reflux. By definition, the patients with pathological GER had higher number of distal esophageal acidic reflux episodes (39[37–48] vs. 18.5[13–25.5], P < 0.01) and distal esophageal AET (5.7 ± 0.5% vs. 1.2 ± 0.2%, P < 0.01) than patients without pathological GER. As predicted from the correlation between gastroesophageal reflux and pharyngeal reflux (Fig. 3), this also translated into substantially higher number of pharyngeal acidic (pH < 6.0) reflux episodes (18[12–23] vs. 10.5[8–14], P < 0.05) and pharyngeal acid (pH < 6.0) exposure time (413 ± 83 s vs. 156 ± 30 s, P < 0.01) in patients with pathological GER. Also, as expected, in patients with pathological GER, the correlations between the number of pharyngeal and distal esophageal reflux episodes GER (r = 0.71, N = 10, P < 0.05) and between duration of pharyngeal acid (pH < 6.0) exposure and distal esophageal acid exposure time (r = 0.63, N = 10, P < 0.05) were numerically stronger than those for the whole group (Fig. 3), although the increase was not dramatic.

Pharyngeal Acidic Reflux Versus Symptoms of LPR and Laryngeal Injury

The symptoms of LPR were quantified by using reflux symptom index (RSI). RSI was available in 26 patients of which 20 patients were RSI-positive and 6 were RSI-negative. The mean RSI in RSI-positive patients was 25.5[24–33.5]. Laryngeal injury was quantified by reflux finding score (RFS). RFS was available in 25 patients of which 21 were RFS positive and 4 were RFS negative. The mean RFS in RFS-positive patients was 10[9—11]. Because our inclusion criteria required positive RSI or RFS, all six RSI-negative patients had positive RFS, and all four RFS-negative patients had positive RSI.

We did not observe a correlation between RSI and RFS in patients in who both RSI and RFS was available (N = 24). This finding indicates that a simple direct relationship between LPR symptoms and laryngeal injury is unlikely. Even when the analysis was performed only in a subgroup of patients who had positive both RSI and RFS, no significant correlation between RSI and RFS was observed (r = 0.31, N = 14, P = NS). Therefore, we performed separate analysis to evaluate the relationships between pharyngeal reflux and symptoms expressed as RSI, and pharyngeal reflux and laryngeal injury expressed as RFS. In order to reduce the probability of false-negative findings, we initially performed the analysis of association between pharyngeal reflux and RSI only in RSI-positive patients, and the analysis of association between pharyngeal reflux and RFS only in RFS-positive patients (Table 2). An identical analysis that was performed on the whole group of patients arrived at identical conclusions (Table 3).

Table 2.

Pharyngeal acidic reflux does not correlate with reflux symptom index (RSI) or reflux finding score (RFS) in patients with LPR (separate analysis in RSI- and RFS-positive patients)

Pharyngeal reflux	RSI-positive patients (N = 20)		RFS-positive patients (N = 21)
	Numbera and durationb of reflux episodes	Correlation with RSI r#1	Numbera and durationb of reflux episodes	Correlation with RFS r#2
pH < 4.0
Number	0[0–1]	− 0.19	0[0–1]	− 0.28
Duration	7 ± 4 s	− 0.17	7 ± 4 s	− 0.34
pH < 4.5
Number	0.5[0–1]	− 0.13	1[0–1]	− 0.06
Duration	18 ± 18 s	− 0.23	19 ± 8 s	− 0.26
pH < 5.0
Number	1[0–2]	+0.06	1[0–3]	− 0.21
Duration	36 ± 16 s	− 0.33	38 ± 16 s	− 0.20
pH < 5.5
Number	3.5[1–6]	+0.10	4[2–7]	− 0.14
Duration	75 ± 25 s	− 0.35	68 ± 22 s	− 0.27
pH < 6.0
Number	13.5[8–23]	+0.21	14[8–21]	+ 0.25
Duration	305 ± 62 s	− 0.26	314 ± 60 s	− 0.03
Upright
pH < 6.0
Number	13[7–21]	+0.21	13[8–19]	+ 0.20
Impedance refluxc [7]
Number	1[1–3]	− 0.20	1[1–3]	− 0.29
Impedance refluxd [25]
Number	0[0–1]	− 0.30	1[0–1]	− 0.36

^aNumber of reflux episodes per 24 h for indicated pH values expressed as median[IQR]

^bDuration of pharyngeal acid exposure per 24 h for indicated pH values expressed as mean ±SEM

^cLPR was defined according to Zerbib et al. [7]. No correlation was found even when upright and supine LPR was analyzed separately (not shown)

^dLPR was defined according to Kawamura et al. [23]. No correlation was found even when upright, and supine LPR was analyzed separately (not shown)

^#1Pearson correlation coefficient r > 0.37 is required for positive directional correlation in RSI-positive patients for significant correlation (P < 0.05)

^#2Pearson correlation coefficient r > 0.36 is required for positive directional correlation in RSF-positive patients for significant correlation (P < 0.05)

Table 3.

Pharyngeal acidic reflux does not correlate with reflux symptom index (RSI) or reflux finding score (RFS) in patients with LPR (all patients)

Pharyngeal reflux	All patients (N = 27)
	Numbera and durationb of reflux episodes	Correlation with RSI r#	Correlation with RFS r#
pH < 4.0
Number	0[0–1]	− 0.29	− 0.07
Duration	6 ± 3 s	− 0.08	− 0.15
pH < 4.5
Number	1[0–1]	− 0.27	+ 0.15
Duration	16 ± 6 s	− 0.10	− 0.04
pH < 5.0
Number	1[0–2]	− 0.23	+ 0.07
Duration	32 ± 12 s	− 0.15	+ 0.00
pH < 5.5
Number	4[1.5–6.5]	− 0.04	− 0.03
Duration	63 ± 18 s	− 0.14	− 0.06
pH < 6.0
Number	14[8–20.5]	+ 0.29	+ 0.23
Duration	279 ± 49 s	+ 0.04	+ 0.11
Upright
pH < 6.0
Number	13[7–18.5]	+ 0.29	+ 0.22
Supine
pH < 6.0
Number	3[1–4.5]	− 0.03	+ 0.00
Impedance refluxc [7]
Number	1[0.5–3]	− 0.29	− 0.07
Impedance refluxd [25]
Number	0[0–1]	− 0.29	− 0.16

^aNumber of reflux episodes per 24 h for indicated pH values expressed as median[IQR]

^bDuration of pharyngeal acid exposure per 24 h for indicated pH values expressed as mean ± SEM

^cLPR was defined according to Zerbib et al. [7]. No correlation was found even when upright, and supine LPR was analyzed separately (not shown)

^dLPR was defined according to Kawamura et al. [23]. No correlation was found even when upright, and supine LPR was analyzed separately (not shown)

^#Pearson correlation coefficient r > 0.32 is required for significant positive directional correlation (P < 0.05)

In order to perform analysis independent of the assumption of how acidic the pH of pharyngeal reflux is required to cause symptoms of LPR or laryngeal injury, we performed analysis for different levels of pH (pH < 4.0, pH < 4.5, pH < 5.0, pH < 5.5, and pH < 6.0). By performing this comprehensive analysis, we found no correlation between acidic pharyngeal reflux and RSI or RFS for any level of acidity (pH). Figure 4a, b illustrates the relationship of pharyngeal acidic (pH < 6.0) reflux and RSI in RSI-positive patients. Figure 4c, d illustrates the relationship of pharyngeal acidic (pH < 6.0) reflux and RFS in RFS-positive patients.

Fig. 4.

Pharyngeal acidic reflux does not correlate with reflux symptom index (RSI) or reflux finding score (RFS) in patients diagnosed with LPR. a, b The relationship between pharyngeal acidic (pH < 6.0) reflux and RSI in RSI-positive (RSI > 13) patients (N = 20, r > 0.37 is required for positive directional correlation for P < 0.05). c, d Relationship between pharyngeal acidic (pH < 6.0) reflux and RFS in RFS-positive patients (N = 21, r> 0.36 is required for positive directional correlation for P < 0.05)

As shown in Fig. 4, there was no correlation between pharyngeal acidic reflux (pH < 6.0) and RSI or RFS. An identical analysis was performed for each evaluated level of acidity of pharyngeal reflux. This analysis is summarized in Table 2 that shows the analysis of correlation of pharyngeal reflux and RSI and RFS in RSI-positive and RFS-positive patients, respectively. The numbers of reflux episodes and the duration of pharyngeal acid exposure are also included in Table 2 to demonstrate that there was no difference in these parameters between the subgroup of patients only positive for RSI and the subgroup of patients only positive for RFS. In addition, no correlation was found when LPR was detected according to impedance-based criteria for dual pharyngeal and esophageal 24-h pH/impedance monitoring developed by Zerbib [7] or Kawamura [25] (Table 2). These results support the conclusion that a direct relationship between pharyngeal reflux and symptoms of LPR or laryngeal injury in LPR patients is unlikely. As noted above, no correlation was found when each of these parameters was analyzed in the whole group of patients (N = 27) (Table 3).

Since the patients with pathological GER had more acidic pharyngeal reflux (see above) we reasoned that the relationship between pharyngeal reflux and symptoms of LPR or laryngeal injury could be detected in these patients. Eight of 20 RSI-positive and 10 of 21 RFS-positive patients had pathological GER. Similar to the findings in the whole group, no direct relationship between pharyngeal reflux and symptoms of LPR or laryngeal injury could be identified in this subgroup of patients with pathological GER (data not shown). Interestingly, there was no difference in RSI (24[18.5–28.5] vs. 24[14.5–34], P = NS) and in RFS (9[8–11] vs. 9.5[7–11], P = NS) between the patients with and without pathological GER.

We also found no significant positive correlation between distal esophageal (gastroesophageal) reflux and symptoms and laryngeal injury in patients with LPR. Distal esophageal acid (pH < 4.0) exposure time (AET) did not correlate with RSI (r = −0.10, N = 20, NS), and there was only a weak trend to correlation between the number of distal esophageal acidic (pH < 4.0) episodes and AET (r = 0.36, N = 20, P = 0.06). RFS did not positively correlate with the number of distal esophageal acidic (pH < 4.0) episodes (r = −0.37, N = 21, NS) or distal esophageal acid (pH < 4.0) exposure time (AET) (r = −0.20, N = 21, NS) (evaluated in RFS-positive patients). No significant correlation of distal esophageal reflux and RSI or RFS was observed when only patients with pathological GER were included in the analysis (analysis not shown).

Discussion

We found no correlation between the pharyngeal reflux as determined by dual pharyngeal and distal esophageal 24-h pH/impedance monitoring and the symptoms and signs attributable to LPR as expressed by RSI and RFS, respectively. No correlation was observed irrespective of the parameter used to quantify pharyngeal reflux that could be determined from pharyngeal and distal esophageal dual-channel pH/impedance 24-h monitoring. We therefore conclude that a direct simple quantitative relationship between pharyngeal reflux and the symptoms and signs attributed to LPR is unlikely. These conclusions are strengthened by three important aspects of our study: (1) detection of pharyngeal reflux based on simultaneous pharyngeal and distal esophageal pH/impedance monitoring, (2) unbiased approach to the quantification of pharyngeal reflux, and (3) enrollment of patients with LPR based on symptoms and signs who are off PPI therapy for at least 30 days.

We used simultaneous dual pharyngeal and distal esophageal pH/impedance 24-h monitoring. The key advantage of this approach is that it allows to establish the gastroesophageal reflux origin of the acidic reflux detected in the pharynx. In other words, it allows to determine that the drop in pH detected in the pharynx is due to gastroesophageal reflux progressing from distal esophagus by evaluating the impedance and pH in both pH sensors. This is indeed a critical consideration inasmuch as the swallowing of food, drink, or saliva also often results in drop in pharyngeal pH. However, the configuration of pharynx and larynx during swallowing is such as to maximally prevent aspiration, and therefore even quite acidic swallows (i.e., carbonated soda drinks) present only a limited or no threat to the airways [27]. In contrast, while upper esophageal reflexes provide important protection of the airways [28], it may be not as effective as that during swallowing, in patients with LPR—i.e., the refluxed acid may be more likely to penetrate into airways.

Thus, in our analysis, we considered as acidic pharyngeal reflux events only those pharyngeal events that originated as acidic gastroesophageal reflux in the distal esophagus. We have also selected the catheter size based on manometrically determined LES and UES such that the proximal pH sensor was approximately 1 cm above the proximal margin of the UES and the distal pH sensor was approximately 5 cm above the proximal margin of the LES. Therefore, we feel confident to assert that the events categorized as acidic pharyngeal reflux in our analysis are due to gastroesophageal reflux.

In addition, we used, in our view, an unbiased approach to quantify pharyngeal reflux. It is unknown how much acid in the pharynx is required to injure laryngeal mucosa. We therefore did not make any a priori assumption about what pH in the pharynx is noxious. Instead, we analyzed pharyngeal reflux events for a complete range of possible pharyngeal pH from pH < 6.0 to pH < 4.0 (pH < 3.0 was not detected in the pharynx in our study). For each pH level, we evaluated both the number of pharyngeal reflux episodes and the cumulative duration of pharyngeal exposure to acid of that pH level. This was done in a manner analogous to quantification of distal esophageal GER by the number of reflux episodes and acid exposure time. Because of this comprehensive analysis, we predict that, if present, any important quantitative relationship would be revealed. Nonetheless, our data indicate that a simple direct relationship between pharyngeal reflux and symptoms or laryngeal injury is unlikely.

It should be noted, however, that the lack of correlation between the symptoms and signs attributed to LPR and the quantitative characteristics of pharyngeal reflux as detected by 24-h simultaneous pharyngeal and distal esophageal pH/impedance monitoring does not rule out that such quantitative relationship exists. It is possible that some quantitative characteristics of LPR that are not adequately captured by 24-h pH/impedance monitoring are important determinants of laryngeal injury. For example, a larger volume of acid during pharyngeal reflux episode would be expected to cause more laryngeal injury. However, the volume of reflux during a pharyngeal reflux episode cannot be determined from pH and impedance monitoring. Although it is probable that longer LPR episodes are associated with larger volumes, there may be wide variations between the volume and duration.

Another possibility is that laryngopharyngeal reflux episodes which are too rare to be sufficiently captured during 24-h monitoring (e.g., do not occur daily) are critical for the intensity of symptoms and laryngeal injury. For example, multiple closely spaced acidic laryngopharyngeal reflux episodes may be effective in inducing laryngeal injury. However, multiple (i.e., 3–5) LPR episodes with pharyngeal pH < 5.0 were only detected in 6 of 27 patients during 24-h monitoring in our study. In our view, this does not necessarily mean that such multiple episodes do not occur in other patients, but only that they did not occur on the day when the monitoring was performed. More prolonged pH/impedance monitoring that may shed more light on this possibility would be prohibitively burdensome.

It is also possible that components of laryngopharyngeal reflux other than acid, which are not detected by pH/impedance, are key for laryngeal injury. Other factors including variability in airway mucosal defense and other predisposing factors unrelated to the amount of laryngopharyngeal reflux may play additional role in determining the intensity of laryngeal injury. Another limitation common to all similar studies of laryngopharyngeal reflux is that the reflux is detected in the pharynx. It cannot be ruled out that extent to which the acidic pharyngeal reflux penetrates into the larynx varies largely between the patients. Finally, it should be also acknowledged that the symptoms and/or laryngeal injury may be not entirely due to laryngopharyngeal reflux in some patients although for patient enrollment we applied stringent criteria common for these types of studies.

Although we primarily focused on the acid (including the acid with pH near 6.0) as a key probable determinant of laryngeal injury [29–31], it is possible that laryngopharyngeal reflux causes laryngeal injury irrespective of its acidity. We therefore added to our analysis an approach of detection of pharyngeal reflux based on impedance as pioneered by other investigators [7, 9, 25]. Similar to our analysis based on pH, no correlation between symptoms and signs attributed to LPR and pharyngeal reflux detected by impedance only was revealed (Table 2). It is important to note that when we applied these impedance-based criteria we observed similar number of LPR events as those reported previously. Specifically, when we used criteria by Zerbib et al. [7] requiring 50% impedance drop in all impedance sensors, we observed the same median number of LPR events (1) as reported by these authors in a similar cohort. Likewise, Dulery et al. [26] found similar median number of LPR events (0) in a cohort of patients that had lower RFS compared to our cohort (5 vs. 9). Several studies evaluated pharyngeal acid exposure and concluded that LPR is relatively uncommon and cannot be detected in most healthy subjects [1, 7, 8, 25].

The studies using dual pharyngeal and distal esophageal pH monitoring but without impedance reported slightly higher number of pharyngeal reflux events then we observed [23, 32, 33]. The reason for this difference has not been explored. Nonetheless, it is possible that adding the impedance and therefore the information on the reflux movement in the esophagus in our study lead to more accurate elimination of acidic pharyngeal events that were not caused by gastroesophageal reflux. Adding impedance probably offers a similar advantage over oropharyngeal pH measurement [9, 23] inasmuch as several studies noted relatively poor correlation between oropharyngeal pH changes and reflux detected by esophageal pH/impedance [1, 3, 9, 34].

Our inclusion criteria were based on positive reflux symptom index (RSI > 13) and/or positive reflux finding score (RFS > 7). In order to increase the chance to detect the quantitative relationship between pharyngeal reflux and the symptoms (quantified by RSI), we separately analyzed only RSI-positive patients for correlation between pharyngeal reflux parameters and RSI. Similarly, we separately analyzed the relationship between pharyngeal reflux and the laryngeal injury (quantified by RFS) only RFS-positive patients for correlation between pharyngeal reflux parameters and RFS. These stringent criteria did not yield a positive correlation (Table 2), similar to the results when the whole cohort was analyzed as a group (Table 3).

Several studies evaluating the relationship between the reflux burden in the hypopharynx and the symptoms or signs of laryngeal injury have been published. A study evaluating LPR and RSI/RFS using dual pH/impedance noted that as a subgroup the patients in who at least one LPR with pH < 4 was detected had slightly higher average RSI (26 vs. 21) than those in who no such event was recorded [35]. The significance of this finding is unknown. In contrast, RFS was virtually identical between these subgroups. Similarly, another study found no significant difference in the number of LPR events between RFS-positive and RFS-negative patients [36]. This is consistent with our findings.

Similar to our results, a recent study using dual-channel pH/impedance also failed to find a correlation between various quantitative parameters of LPR and RSI [37]. However, a marginal correlation between the total number of LPR events and RFS was reported in another study [36]. Most studies using dual-channel pH monitoring without impedance found no correlation between LPR and symptoms and signs of laryngeal injury [32, 38], although some noted certain differences between the patients with and without detectable LPR [33]. Finally, oropharyngeal pH monitoring uncovered no differences in RFS between the patients with and without LPR as determined by this method [39]. In conclusion, despite various differences in patient selection, the method of LPR detection, and the parameters analyzed, most studies are in agreement with our conclusions. The simple direct relationship between pharyngeal reflux and symptoms or laryngeal injury is therefore unlikely.

It should be recognized that the studies of LPR have a common limitation in that there is no gold standard established for the diagnosis of LPR. Therefore, it is not possible to definitely establish whether the problems in a given patient are due to laryngopharyngeal reflux. Therefore, it cannot be ruled out that in some patients included in our study, the symptoms were not caused by laryngopharyngeal reflux. We attempted to diminish the effect of such inclusions by performing separate analysis based on RSI alone and RFS alone, which led to the same conclusions. It should be also noted that our study group of patients is similar to the population that is in clinical practice considered to have LPR based on signs and symptoms, and that our conclusions are therefore applicable to this patient population. Unfortunately, until a reliable diagnostic test is available one is forced to use standard diagnostic criteria (RSI, RFS) despite their limitations. Some researches argue that the objective findings (RFS) are more indicative of the disease while symptom scores (RSI) have no value in the diagnosis of LPR. While this is a reasonable consideration, we found no correlation between RFS and hypopharyngeal reflux, even when only the subgroup of subjects with positive RFS was analyzed (Table 2). The usefulness of RSI and RFS in diagnosis of LPR will need to be evaluated in the light of information gained from studies employing pharyngeal reflux monitoring.