自己免疫性胃炎とH. pylori感染とその除菌との関連

Relationship among Autoimmune Gastritis, H. pylori Infection and H. pylori Eradication

要旨●自己免疫性胃炎には，H. pylori感染の関与がある場合とない場合があり，両者間で胃体部や前庭部での萎縮や慢性炎症性変化に違いを認める．いずれも胃酸分泌が著しく低下しており，H. pylori以外の細菌が胃内に棲息でき，その中にはウレアーゼ活性を有する菌もあり，¹³C-尿素呼気試験（¹³C-UBT）が陽性となる．H. pylori感染胃炎では除菌後に胃酸分泌が改善するため，H. pylori以外の細菌は棲息しにくいが，自己免疫性胃炎では胃酸分泌は低下したままであり，引き続きウレアーゼ活性陽性細菌が棲息でき，¹³C-UBTの陽性が継続するため除菌失敗と判断されて除菌療法が繰り返される，いわゆる“泥沼除菌”状態となるため注意が必要である．また，もともとH. pylori未感染であってもH. pylori感染診断に¹³C-UBTを用いた場合は，H. pylori陽性と判断され，“泥沼除菌”に陥りやすい．

　There are following two types of autoimmune gastritis（AIG）：H. pylori-related AIG and H. pylori-unrelated AIG. These types of AIG significantly differ in terms of atrophy of the corpus callosum and chronic inflammation of the antrum. In both types of AIG, gastric acid secretion is remarkably impaired, allowing bacteria other than H. pylori to inhabit the stomach. Some of these bacteria have urease activity, leading to positive results of¹³C-UBT（¹³C-urea breath test）. Because gastric-acid secretion is improved after the eradication in cases of H. pylori-induced gastritis, bacteria other than H. pylori have difficulty colonizing the stomach. However, in cases of H. pylori-related AIG, gastric-acid secretion is not restored after the eradication of H. pylori, allowing urease-positive bacteria to inhabit the stomach after the eradication. Therefore, the results of ¹³C-UBT remain positive and failure to eradicate H. pylori is diagnosed. This misdiagnosis leads to further eradication therapies or endless eradication（doronumajokin）. In cases of H. pylori-unrelated AIG, the results of the ¹³C-UBT are also positive because of the above-mentioned reasons, leading to doronumajokin.