A very tall order for single-operator cholangioscopy

We read with great interest the study by de Vries et al. [1] reporting on the diagnostic accuracy of single-operator peroral cholangioscopy (sPOCS), which seems to run contrary to the trend of recent findings [2].

We believe the underlying issue for most studies in this field is conceptual: overlooking Bayes’ theory and its practical implications [3]. The “one-size-fits-all” approach places sPOCS in the untenable position of having to simultaneously rule in and rule out cancer with high accuracy ([Fig. 1]). The authors acknowledge the high percentage of primary sclerosing cholangitis (PSC) patients in their cohort (40 %) as a limitation [4] but underestimate its practical importance.

Fig. 1 A visual representation of the challenge of applying the same diagnostic test (i. e. single-operator peroral cholangioscopy) in two types of population: high risk and low risk for malignancy, respectively. Highlighted bars represent the target population in each clinical scenario (constructed using the Two by Two Diagram display and calculator. http://54.221.244.58:3838 /Truth/). T + true positive; T- true negative; F + false positive; F- false negative; CCA cholangiocarcinoma; PSC primary sclerosing cholangitis.

In PSC patients, the endoscopist is called to rule out cancer, as the pretest probability of malignancy is much lower (< 10 %) [5] than that of non-PSC-related strictures. Applying the positive and negative likelihood ratios reported in this study for sPOCS biopsy and brush cytology, we calculated that they could increase the post-test probability of malignancy from 50 % to 86 % and 99 % respectively in a high-risk population (50 % incidence of cancer) while, in a low-risk setting, sPOCS biopsy could not significantly decrease the post-test probability of malignancy. This underscores the caveats of conducting diagnostic tests without focusing on the relevant clinical end points.

Publication History

Article published online:
26 August 2020

• References

• 1 de Vries AB, van der Heide F, ter Steege RWF. et al. Limited diagnostic accuracy and clinical impact of single-operator peroral cholangioscopy for indeterminate biliary strictures. Endoscopy 2020; 52: 107-114
• 2 Gerges C, Beyna T, Tang RSY. et al. Digital single-operator peroral cholangioscopy-guided biopsy sampling versus ERCP-guided brushing for indeterminate biliary strictures: a prospective, randomized, multicenter trial (with video). Gastrointest Endosc 2020; 91: 1105-1113
• 3 Johnson KM. Using Bayes’ rule in diagnostic testing: a graphical explanation. Diagnosis (Berl) 2017; Erratum in: Diagnosis (Berl) 2018; 5: 89 4: 159-167
• 4 de Moura EGH. Limited diagnostic accuracy and clinical impact of single-operator peroral cholangioscopy for indeterminate biliary strictures. Endoscopy 2020; 52: 90-91
• 5 Razumilava N, Gores GJ, Lindor KD. Cancer surveillance in patients with primary sclerosing cholangitis. Hepatology 2011; 54: 1842-1852