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NBI optical diagnosis of small polyps inadequate outside expert centers
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Narrow band imaging-assisted optical diagnosis of small colorectal polyps cannot currently be recommended in routine clinical practice outside of academic centers, according to the results of the Discard 2 study, which found the accuracy of the technique was inadequate.
“Optical diagnosis to characterize colorectal polyps has been shown to be accurate in expert hands. A discard policy of characterizing polyps and then discarding them has been proposed,” Colin J. Rees, MD, from the department of gastroenterology at South Tyneside District Hospital in the U.K., told Healio Gastroenterology. “Discard 2 sought to study whether these results were generalizable to routine clinical practice.”
Discard 2 was a prospective, blinded study involving 1,688 adults who underwent routine colonoscopy at six general hospitals in the U.K. between July 2012 and February 2014.
Twenty-eight participating colonoscopists received training on NBI in polyp characterization using a validated training module, including the use of NICE classification.
During colonoscopy, polyps less than 10 mm in size were evaluated with both white light and NBI. The colonoscopists classified each polyp using NBI and NICE classification, recorded their diagnostic confidence level, and assigned a surveillance interval. Then blinded histopathologists classified the specimens, and blinded investigators assigned surveillance intervals.
Optical and histologic findings were then compared, with presence of adenoma and need for surveillance serving as the primary outcome measures.
Overall, 722 patients had small or diminutive polyps, 78.5% of whom had only polyps less than 10 mm in size (mean age, 64.3 years; 53.1% men).
Based on the threshold of the presence of at least one adenoma, optical diagnosis was performed with 83.4% sensitivity (95% CI, 79.6-86.9), and based on correctly identifying need for surveillance, the sensitivity was 73% (95% CI, 66.5-79.9. “Both measures were considerably lower than the 95% requirement (P < .001) set by the study team,” the researchers wrote.
Polyp-level analysis of 1,620 total polyps based on correct identification of adenomas showed optical diagnosis was performed with 76.1% sensitivity (95% CI, 72.8-79.1), while fully adjusted analysis showed optical diagnosis was performed with 99.4% sensitivity (95% CI, 98.2-99.8) if at least two NICE adenoma characteristics were identified.
Colonoscopist expertise, confidence in diagnosis and use of high definition colonoscopy were not found to independently improve test accuracy.
“Discard 2 demonstrated that in routine clinical practice clinicians could not accurately differentiate between hyperplastic and adenomatous polyps,” Rees said. “A discard policy cannot yet be recommended for routine clinical practice. Further work is required to determine whether polyps did not demonstrate the key diagnostic features or whether clinicians were able to accurately identify them.” – by Adam Leitenberger
Disclosure: Several researchers report they have received research, travel and speaking funding from Olympus Medical and other endoscopy companies.
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