TO THE EDITOR: With great interest, we read the article of Hsing et al¹ The authors assessed correlation of the diagnostic parameters of functional luminal imaging probe (FLIP) panometry and high-resolution manometry and Eckardt scores. Those parameters were compared before and after peroral endoscopic myotomy (POEM), and those changes were differentially revealed that the patients who showed repetitive antegrade contraction (RAC) and/or diagnosed as achalasia II before POEM were most likely resulted in presence of contractility (POC), a normal contractile response to sustained esophageal distension.

A total of 68 achalasia patients underwent POEM were monitored upon measurements as shown in Table 1. Pre-POEM, those patients had similarities in Eckardt score and FLIP motility esophagogastric junction–distensibility index (EGJ-DI) compared in 3 subtypes of achalasia; post-POEM in follow-up 36 patients, Eckardt score was overall achieved < 3 (P < 0.01), integrated relaxation pressure was decreased to < 15 mmHg (P < 0.01) and EGJ-DI > 8 (P < 0.01). Authors obtained a good efficacy of POEM in consistent to other studies.^2,3 However, all of those cannot be for prediction in correlative to POEM efficacy. Thus, Hsing et al¹ suggested that the POC is one of critical indexes reflecting a good restoration of motility function of lower esophagus sphincter, which was seen in 8%, 67%, and 25% respectively from type-I, -II, and -III achalasia after POEM, ie, there is a better expectation from POEM in achalasia subtype II than I or III. Furthermore, the POC was absolutely not seen when RAC(–), and all other important parameters indicating improvement changes do not correlate to POC as shown in Table 2. Clearly, that the method of RAC is one of features of achalasia II and is a prognosis for therapeutics were based on older criteria of RAC. The modified version of the rule of repetitive antegrade contractions states that if > 6 repetitive RACs occur at least 6 cm in axial length at a rate of 6 ± 3 per minute.⁴ It is widely recognized that contractile response meeting the RAC Rule-of-6s was found in 95% of asymptomatic controls and < 1% of achalasia patients.⁵ Therefore, the conclusion based on RAC in discretion of prognosis among subtypes of achalasia by Hsing et al¹ needs further quantifying (distension induced contractility) and clarifying. Similar issue by using the older criteria of “repetitive retrograde contractions” is raised, which likely limits the specificity of this application as well.

Table 1 . Baseline of Part of Diagnosis in Achalasia Patients Before Peroral Endoscopic Myotomy

Achalasia patient	Type I (n = 14)	Type II (n = 39)	Type III (n = 15)	P-value
HRM
IRP (mmHg)	20.0 ± 0.0	34.2 ± 13.9	33.2 ± 10.9	0.011
Basal EGJ (mmHg)	14.0 ± 1.0	42.0 ± 19.4	53.1 ± 32.9	0.008
Eckardt score	6.43 ± 1.9	6.77 ± 2.4	5.8 ± 1.97	0.369
FLIP motility
EGJ-DI (mm2/mmHg)	2.3 ± 1.6	1.4 ± 0.9	1.6 ± 1.1	0.278

HRM, high-resolution manometry; IRP, integrated relaxation pressure; EGJ, esophagogastric junction; FLIP, functional luminal imaging probe; EGJ-DI, EGJ-distensibility index.

Total 68 achalasia patients were diagnosed, and further categorized patients 14 in subtype I, 39 in II and 15 in III, as labeled in brackets. The measurements of IRP and basal pressure of EGJ from manometry were existed in significantly different compared between subtypes of achalasia, indicating the obstructive at the esophagogastric junction different. Whether or not such difference could be brought up efficacy difference under peroral endoscopic myotomy (POEM) is expected. Both of Eckardt scores and EGJ-distensibility were overall similar among subtypes of achalasia, obviously, symptomatic improvements were not be discernable in association of their roles for prognosis in post-POEM.

Data are presented as mean ± SD.

Table 2 . The Association of Parameters to Presence of Contractility at Post-peroral Endoscopic Myotomy

Variables	Without POC group (n = 12)	With POC group (n = 24)	P-value
Achalasia subtype			0.007
Type I	6	2
Type II	6	16
Type III	0	6
RAC			0.008
RAC(–)	4	0
RAC(+)	8	24
RRC			0.384
RRC(–)	1	6
RRC(+)	11	18
FLIP topography classification			0.128
REO retrograde contractile response	7	17
REO absent contractile response	0	2
REO normal contractile response	1	4
Retrograde contractile response	4	1
Pre-POEM Eckardt score	6.00 ± 2.30	6.88 ± 2.58	0.327
Post-POEM Eckardt score	1.08 ± 0.10	1.29 ± 1.43	0.654

POC, presence of contractility; RAC, repetitive antegrade contraction; RRC, repetitive retrograde contraction; FLIP, functional luminal imaging probe; REO, reduced esophagogastric junction opening; POEM, peroral endoscopic myotomy.

In follow up of total 36 patients, patients without and with POC were respectively 12 and 24 (indicated in brackets). In composition of POC analysis, type II is predominant ie, 67%, indicating type II is one of predictive value to achieve good efficacy under POEM. Only patients who had RAC were observed with POC, strongly indicating RAC is one of predictive value to achieve good efficacy under POEM. Other parameters including RRC and FLIP panometry (such as REO) were not significantly associated to POC.

Data are presented as n or mean ± SD.

The repetitive contractility including repetitive antegrade contraction was observed in this study with functional luminal imaging probe panometry which greatly triggered our interests, eg, do such contractions in achalasia have a neurogenic or myogenic origin? Does such activity only present in early achalasia? Our hypothesis is that while loss of nitrerigic inhibition from both of neural and myogenic sources, then the stimulation is likely a forceful contraction, a pure myogenic control system is not capable of fulfilling propulsive contractions, whereas, POEM restores such device in work.

In conclusion, findings by Hsing et al¹ lead to medical and scientific implications. Firstly, the better functional recovery after POEM from achalasia subtype II suggests that impaired neuronal function limited to the lower esophagus sphincter cholinergic/nitrergic imbalance may be prominent in achalasia.^5,6 Secondly, achalasia patients with RACs may be as one of criteria in favor for POEM while hesitating with other therapeutics. Future studies are expected to answer the mechanism of RACs and to narrow down the application of POEM. An explanation on why POC after POEM did not appear to be associated with improved clinical outcomes is our curious, or, the further analysis is to pose for future study.

None.

None.

Meng Xia and Yu-Lin Chen equally contributed to this paper. Meng Xia and Yu-Lin Chen wrote the draft; and Jianlin Lv as corresponding author made revisions and corrections on the manuscript.