Can the wet suction technique change the efficacy of EUS-FNA for diagnosing autoimmune pancreatitis type 1? A prospective single-arm study

Background: Other than surgical biopsy, endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) is the only method for histologically diagnosing autoimmune pancreatitis (AIP). However, adequate specimens are difficult to obtain. Recently, more adequate specimens were reported to be obtained with a wet suction technique (WEST) of EUS-FNA than with the conventional method of EUS-FNA. This study aimed to histologically diagnose AIP by EUS-FNA with a WEST. Methods: Eleven patients with possible type 1 AIP between February 2016 and August 2018 underwent WEST EUS-FNA (WEST group) with four punctures with 19 or 22 G needles. As a historical control, 23 type 1 AIP patients who underwent no fewer than four punctures with 19 or 22 G needles were selected (DRY group). Patient characteristics and histological findings were compared between the two groups. Results: Three histopathological items of the International Consensus Diagnostic Criteria were significantly greater in the WEST group than the DRY group (n (%), lymphoplasmacytic infiltrate without granulocytic infiltration: 9 (81.8) vs 6 (26.1), p value=0.003, storiform fibrosis: 5 (45.5.) vs 1 (4.3), p value=0.008, abundant (>10 cells/HPF) IgG4-positive cells: 7 (63.6) vs 5 (21.7), p value=0.026). Level 1 or level 2 histopathological findings were observed more in the WEST group than in the DRY group (n (%) 8 (72.7) vs 3 (13.0), p value=0.001). Conclusions: WEST EUS-FNA was more useful than standard EUS-FNA for histologically diagnosing AIP. Background This study was a single arm prospective study intended to clarify the efficacy of WEST EUS-FNA for diagnosing type 1 AIP. This study was performed at Fukushima Medical University. This study was approved by the Institutional Review Board of Fukushima Medical University. All patients agreed to participate in this study. This trial was registered in UMIN (ID: 000019768).

However, histological diagnosis of AIP requires level 1 pancreatic histological findings.
Apart from surgical biopsy, endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) is the only method used to histologically diagnose AIP. Nevertheless, it is very difficult to obtain an adequate specimen [4][5][6]. In the ICDC, EUS-FNA was recommended for ruling out malignancy before a diagnostic steroid trial [3]. In fact, Sugimoto et al. [7]reported that the clinical characteristics of pancreatic cancer differed from those of AIP and that EUS-FNA could be used to rule out malignancy in AIP patients.
However, recently, with a wet suction technique (WEST) of EUS-FNA, more adequate specimens were reported to be obtained than by the conventional method of EUS-FNA [8].
Therefore, we hypothesized that more AIP patients could be histopathologically diagnosed by WEST EUS-FNA.

Study design and ethics
This study was a single arm prospective study intended to clarify the efficacy of WEST The method of WEST EUS-FNA All procedures were performed under the guidance of a professional endoscopist who was well versed in EUS-FNA (TT) and who had performed no less than 1500 EUS-FNA procedures. After a patient was well sedated with intravenous midazolam, an echoendoscope was inserted. The swollen pancreas was viewed on the monitor, and the vessels along the puncture line were confirmed by color doppler echo imaging. Then, the puncture needle was prepared for WEST. The WEST EUS-FNA was performed according to the methods in a previous report by Attam et al [8]. First, the stylet was removed from the needle, and saline solution was injected into the needle (Figure 2A). After a suction syringe was loaded to 20 ml of suction in a locked position, the syringe was set at the edge of the needle without an extension tube ( Figure 2B). The needle was inserted into the target lesion, and the lock of the suction syringe was opened. Saline solution flowed into the suction syringe because of the negative pressure ( Figures 2C and D), and the needle was moved back and forth 20 times per puncture. The punctures were performed 4 times according to the instructions in the past report by Suzuki et al [9].
In the WEST group, the echoendoscope used was GF-UC240AL-5 or GF-UCT260 (Olympus Medical Systems, Tokyo, Japan

Sample size
The results of conventional EUS-FNA for AIP type 1 patients in our hospital indicated that level 1 or level 2 histopathological findings were observed in 13% (3/23) of patients. The results of WEST EUS-FNA were expected to be 60%, which was better than a previous multicenter study [11]. Eleven patients were needed in this study for an α error of 0.05 and statistical power of 0.8. University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). EZR is a modified version of R commander that was designed to perform functions that are frequently used in biostatistics [12].

Results
Patient characteristics were not significantly different between the WEST and DRY groups except for sex (Table 1). Females were significantly more common in the WEST group than in the DRY group (male/female, WEST group 6/5, DRY group 21/2, p value = 0.024).
Regarding the comparison of procedures and results related to EUS-FNA, several items were significantly different between the two groups ( Table 2). The number of needle passes was significantly lower in the WEST group than in the DRY group (median (range), In Figure 3, a representative case of a patient diagnosed with AIP by WEST EUS-FNA is shown.

Discussion
In this study, we investigated the efficacy of WEST EUS-FNA for diagnosing AIP. Three histopathological items according to the ICDC were observed more frequently in the WEST group than in the DRY group. Level 1 histopathological findings and level 2 histopathological findings were observed more in the WEST group than in the DRY group.
Regarding EUS-FNA for AIP, the results of procedures performed with standard needles and more complex needles were reported. Regarding previous reports using standard needles, Iwashita et al. [13]reported that performing EUS-FNA with a 19 G needle resulted in a diagnosis of AIP in 17 of 44 cases. The reports using a 22 G needle are described below.
Ishikawa et al. [4]diagnosed LPSP in 9 of 47 AIP patients. Imai et al. [5]could not histopathologically diagnose AIP. Interestingly, a multicenter study found that the diagnosability of AIP by EUS-FNA was poor [6], and another multicenter study reported that 57.7% of patients were diagnosed with level 2 or higher based on the histopathological findings [14] .
Second, some previous reports involved more complex needles. Mizuno et al. [15]reported that 45.5% of AIP patients were diagnosed with LPSP using EUS Tru-Cut biopsy (EUS-TCB) needles. In a report by Kanno et al. [11], level 1 and 2 histological findings were observed in 56% and 24% of AIP patients, respectively, by EUS-FNA using 22 G automated springloaded PowerShot needles. The histopathological diagnosability of EUS-FNA for AIP was improved by needle choice; however, it was difficult to statistically compare the sensitivity and accuracy between the standard needles and more complex needles.
On the other hand, the histopathological accuracy by WEST EUS-FNA was statistically superior to that by the standard EUS-FNA method or EUS-TCB in this study (seven historical control cases underwent EUS-TCB). Moreover, the positive result of this study was achieved with standard needles. Though the reasons underlying the increased size of the specimens collected by WEST are not clear, it is thought that the saline solution coating the lining of the needle leads to better transmission of the applied suction or that the saline solution acts as a stylet, reducing the contamination from GI tissue [8].
Recently, the efficacy of EUS-FNA using a 22 G SharkCore needle was reported for the diagnosis of AIP [16,17]. By the development of puncture methods such as WEST or special puncture needles, the diagnosability of AIP by EUS-FNA will be improved.
This study had some limitations. First, this study was performed with a small sample size in a single institution. Second, historical controls were used as a control group. In the future, a multicenter randomized controlled trial (RCT) with more cases is needed.
However, AIP patients are rare, rending an RCT difficult to conduct. Third, we used EUS-TCB needles such as ProCore 19 G or Quick-Core 19 G (Cook Medical Inc., NC, USA) in the historical control patients. Although these needles have been reported to increase the yield of samples [18,19], these needles were not used in the WEST group. Therefore, they were not a factor in the superiority of the WEST technique.

Conclusion
WEST EUS-FNA was more useful for histologically diagnosing AIP than was standard EUS- Availability of data and materials The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.
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