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Electronic letters published:
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Limitations of virtual colonoscopy from the patient and gastroenterologist¡¯s perspective
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Inku Hwang, MD Walter Reed Army Medical Center, Roy K.H. Wong
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Inku.Hwang{at}NA.AMEDD.ARMY.MIL Inku Hwang, et al.
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TO THE EDITOR: Recently, the miss rate of optical colonoscopy (OC) using virtual colonoscopy (VC) was reported in Annals as 12% for polyps ¡İ 10mm (1). This and the NEJM VC paper where this data originates (2) sheds a very favorable light on VC. As co-investigators in the original NEJM study and as gastroenterologists, we would like to point out aspects of this data that have not yet been advertised to cast a more balanced view of VC. Although sensitivity and specificity of VC in the NEJM study were high, VC had a high false positive (FP) rate of 51.1% for polyps ¡İ 10mm per patient (47/92, 95% CI 40.4-61.7%) and a low positive predictive value (PPV) of 48.9% (45/92, 95% CI 38.3-59.6%). For polyps ¡İ 6mm, the FP rate was 59.3% (217/366, 95% CI 54.1-64.4%) with a PPV of 40.7% (149/366, 95% CI 35.7-45.9%) (2). Thus, if patients with polyps ¡İ 6mm on VC were referred for OC, 217 would have potentially received unnecessary OC¡¯s. Similar results were recently reported by Van Gelder with VC FP rate of 41% for polyps ¡İ 10mm and 64% for polyps ¡İ 6mm (3). Incidentally, the OC miss rate in that study was 17% for polyps ¡İ 10mm. Admittedly, sensitivity and specificity are more important for a screening test of a low prevalence disease. However, when the test is expensive, uncomfortable and risks high radiation exposure, the issue becomes more complex. From the patient and the endoscopist¡¯s perspective, the high FP rates and low PPV's are problematic, as findings on VC may represent low likelihood of true disease. Thus, patient¡¯s anxiety about the results, and extra time spent by endoscopists may not be warranted. This high FP rate also reduces the benefit of pre-selection. These concerns have been more than academic at our institution where we have been using VC for screening. Ultimately, despite criticism by some that VC may be an inaccurate test with sensitivity and specificity as low as 55% for polyps ¡İ 10mm (4), we believe it has a role for screening when performed correctly. However, results may vary with different software, protocols and technologies. Thus, when applied on a broad scale it may not be as good as originally promised, and its shortcomings may not be apparent from initial reports. VC has limitations we need to understand before we embrace it as the standard of care for routine clinical practice. Inku Hwang, MD Roy K.H. Wong, MD Walter Reed Army Medical Center Washington, DC 20307 References: 1. Pickhardt PJ, Nugent PA, Mysliwiec PA, Choi JR, Schindler WR. Location of adenomas missed by optical colonoscopy. Annals of Internal Medicine. 2004;141(5):352-9. 2. Pickhardt PJ, Choi JR, Hwang I, et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults.[see comment]. New England Journal of Medicine. 2003;349(23):2191- 200. 3. Van Gelder RE, Nio CY, Florie J, et al. Computed tomographic colonography compared with colonography in patients at increased risk for colorectal cancerl. Gastroenterology. 2004;127(1):41-8. 4. Cotton PB, Durkalski VL, Pineau BC, et al. Computed tomographic colonography (virtual colonoscopy): a multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA. 2004;291(14):1713 -9. Conflict of Interest:None declared |
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