Unusual Helicobacter pylori in gastric resection specimens: an old friend with a new look.

Immunohistochemical staining is useful in the diagnosis of Helicobacter pylori-induced gastritis. The authors encountered gastric resection specimens with an unusual pattern of reactivity on H pylori immunostains where the typical morphology of the organism was not recognizable, but the characteristic chronic gastritis associated with infection was present. The authors sought to explore this phenomenon by retrospectively reviewing and immunostaining 28 gastric resection specimens for H pylori. Six cases with large clumps of immunohistochemically positive but morphologically unrecognizable material were identified on light microscopy, corresponding on electron microscopy to clusters of predominantly coccoid H pylori, some located intracellularly. Such organisms were not identifiable without immunohistochemistry, and the phenomenon was not encountered in gastric biopsies. The authors conclude that this staining pattern reflects true H pylori infection that is not diagnosable without immunohistochemistry. Based on its occurrence only in resections, it may be the result of hypoxic or other stress induced when the mucosa is not promptly fixed.