Is there a clinical significance to the development of squamous islands in Barrett's mucosa under treatment?
R.E. Sampliner (Tucson)
A majority of patients in the long term proton pump inhibitor trials have developed squamous islands in the Barrett's mucosa. These islands may represent a form of regression or a superficial change with persistence of underlying intestinal metaplasia. Over time, these islands have been observed to merge into peninsulas that can ultimately involve a major portion of what had previously been Barrett's epithelium. Extension of patchy zones of squamous epithelium into areas of Barrett's mucosa was initially described in 2 patients after antireflux surgery . Another carefully documented case demonstrated the development of squamous islands overlying intestinal metaplasia after fundoplication . Microscopic squamous mucosa overlying intestinal metaplasia was recognized in biopsies of 6 of 45 patients with Barrett's esophagus treated with H2-receptor antagonists without prior antireflux surgery . Microscopic squamous islands with underlying intestinal metaplasia have also been documented in a proton pump inhibitor trial .
In a study evaluating the 24-hour pH of a group of patients on long-term proton pump inhibitor therapy, an increase in the number and size of squamous islands was observed in both the group with pH control and the group with persisting abnormal esophageal acid exposure . This suggests that normalization of esophageal acid exposure is not necessary for the development of squamous islands.
Squamous re-epithelialization of the esophagus could speculatively occur as a result of enlarging squamous islands and the growth of squamous epithelium adjacent to the squamocolumnar junction. The significance of the development of squamous islands is not clear. These islands could reflect sites of biopsy where Barrett's epithelium has been removed and repopulated with squamous epithelium in patients on proton pump inhibitor therapy. Only follow-up of larger numbers of patients with systematic biopsies of islands will help to establish their significance. Evaluation of biologic markers and growth factors in the microenvironment may help in better defining the significance of squamous islands.
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