Lewis et al,1 in their meta-analysis, report a prevalence of isolated advanced proximal neoplasia ranging from 2% to 5%, with a pooled estimate of 2.4%. However, the prevalence rates from the individual studies were calculated by including only subjects who had negative flexible sigmoidoscopy findings. This calculation is biased, since it does not reflect when a patient is counseled regarding the differences between flexible sigmoidoscopy and colonoscopy in the decision-making process. The appropriate time for a patient to be counseled about the yields of the 2 tests is prior to the initiation of either test. Thus, the correct prevalence is the prevalence of isolated advanced proximal neoplasia in all subjects presenting for screening. Using that denominator, the prevalence of isolated advanced proximal neoplasia in the screening colonoscopy studies is 1.2%2 and 2.1%, respectively,3 not 2% and 3% as reported in Figure 4 B. By including only subjects with negative sigmoidoscopy findings, Lewis et al1 have overestimated the prevalence of isolated advanced proximal neoplasia. If a practitioner is going to attempt to influence the patient to have a full colonoscopy after a negative flexible sigmoidoscopy, then there is no point in performing the sigmoidoscopy.
Schoen RE. Prevalence of Isolated Advanced Proximal Neoplasia. Arch Intern Med. 2003;163(17):2103. doi:10.1001/archinte.163.17.2103-a
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