The needle-based confocal endomicroscopy (nCLE) probe was first approved by the Food
and Drug Administration (FDA) in 2013. In a “white paper” published by the American
Gastroenterology Association, competency-based training of novel endoscopic imaging
techniques was emphasized compared to the traditional volume-based model of procedures
[1]. We define competency as the ability to recognize diagnostic image patterns in nCLE.
Only with familiarity of these patterns, can the endoscopist acquire them during the
procedure. While competency needs to be achieved before physicians start enrolling
patients in a prospective study, image acquisition quality also needs to be continually
monitored during the study process to evaluate the learning curve and detect any potential
deficiencies.
In the study by Keane et al., a prospective trial of CONfocal endomicroscopy in CYSTic
lesions of the pancreas (CONCYST), there is concern regarding the images demonstrated
in their Fig. 1 [2]. The interpretation of study results and less than superior diagnostic accuracies
in the evaluation of pancreatic cystic lesions are hence questioned. The representative
images of intraductal papillary mucinous neoplasm (IPMN), serous cystadenoma (SCA),
and pseudocyst do not appear to be accurate. High-quality imaging during EUS-guided
needle-based confocal endomicroscopy (EUS-nCLE) is critical before realizing the diagnostic
accuracies of these novel investigative modalities. Moreover, accurate interpretation
of nCLE images is also equally important.
The nCLE images are broadly classified into epithelial and vascular patterns [3]
[4]. The following are the four major studies evaluating EUS-nCLE.
(i) The INSPECT study [5] (2013). This was the first multicenter study that included 66 patients from eight
centers in the US and Europe. This trial focused on the characterization of IPMNs.
EUS-nCLE revealed papillary structures that were IPMNs (sensitivity of 59 %, specificity
of 100 %, and accuracy of 71 %). The overall complication rate was 9 %.
(ii) The DETECT study [6] (2015). This single center US study showed improved diagnostic parameters. EUS-nCLE
had a sensitivity of 80 %, specificity of 100 %, and accuracy of 89 % for the diagnosis
of IPMNs.
While the INSPECT and DETECT studies had lower sensitivity, the next two trials revealed
higher sensitivity mostly due to discovery of image patterns in SCAs, and mucinous
cystic neoplasms (MCNs).
(iii) The CONTACT study [4]
[7] (2018). This multicenter European study defined novel diagnostic patterns for SCAs,
MCNs, and cystic neuroendocrine tumors; hence, the diagnostic parameters were much
improved for detecting premalignant pancreatic cystic lesions (PCLs) (sensitivity
91 %, specificity 95 %, accuracy 94 %).
(iv) The INDEX study [3]
[8]
[9] (2019). This single center US study compared in vivo and ex vivo CLE to surgical
histopathology. For diagnosing premalignant mucinous PCLs, the sensitivity, specificity,
and accuracy were 98 %, 94 %, and 97 %, respectively. This study, thus far, had the
highest number of patients with definitive surgical histopathology (n = 65) [9].
While earlier EUS-nCLE studies revealed lower sensitivity, the more recent trials
have demonstrated improving diagnostic accuracies with the discovery of additional
image patterns. Future clinical trials evaluating EUS-nCLE should emphasize the acquisition
of high-quality images by implementing physician training and have periodic assessments
on competency.