A very tall order for single-operator cholangioscopy
We read with great interest the study by de Vries et al.  reporting on the diagnostic accuracy of single-operator peroral cholangioscopy (sPOCS), which seems to run contrary to the trend of recent findings .
We believe the underlying issue for most studies in this field is conceptual: overlooking Bayes’ theory and its practical implications . 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  but underestimate its practical importance.
In PSC patients, the endoscopist is called to rule out cancer, as the pretest probability of malignancy is much lower (< 10 %)  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.
26 August 2020 (online)
© Georg Thieme Verlag KG
Stuttgart · New York
- 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
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