腸管スピロヘータ症（intestinal spirochetosis）―自験34例からみた内視鏡像・臨床的意義・治療

Intestinal Spirochetosis─Endoscopic Findings, Clinical Significance, and Treatment Based on Observations in 34 Cases

要旨　腸管スピロヘータ症（intestinal spirochetosis）は，グラム陰性桿菌であるBrachyspira属を原因菌とする人畜共通感染症で，病理組織学的に大腸上皮表面に好塩基性で毛羽立ち状に付着した特徴ある菌塊が観察される．自験34例の検討から，その頻度は0.19％で，比較的若年の男性に多く，自覚症状を欠く場合や基礎疾患に合併し偶然見つかる症例が多かった．またアメーバ性腸炎に合併する症例が多く，注目すべき事項であった．スピロヘータは全大腸に分布してみられ，明らかな好発部位や，下痢症状との相関は指摘できなかった．特徴的な内視鏡像はなく，病理組織学的に粘膜内の強い炎症像はほとんどみられなかった．スピロヘータはBrachyspira aalborgi と推測される5μm前後の短い菌と，Brachyspira pilosicoli と推測される10μm前後の長い菌の2種類あり，多くが前者であった．腸管スピロヘータ症を臨床的，内視鏡的に診断することはほとんど不可能で，病理組織学的にも見落とされる場合が多くあるため注意深い丹念な観察が必要である．またスピロヘータの感染のみで強い炎症像を呈することはほとんどないため，その場合は他疾患の合併，特にアメーバ性腸炎などの合併を考慮し再評価する必要があると考える．

　Intestinal spirochetosis is a zoonotic infection caused by gram-negative bacilli belonging to the genus Brachyspira. Histopathologically, it is characterized by being basophilic and flocculent colonies that adhere to the epithelial surface of the large intestine. Our experience in 34 cases indicated that the frequency of intestinal spirochetosis is 0.19％, it is commonly seen in relatively young males, and often lacks subjective symptoms but is found incidentally because of complications in underlying diseases. It should be noted that many cases were found as complications of amebic colitis. Spirochetes were distributed all over the large intestine, and did not show any clear preference for a specific site（s）or correlation with diarrhea. No characteristic endoscopic findings were observed, and hardly any severe inflammation on the membrane was observed on histopathological examination. Two types of spirochetes were present : one approximately 5μm in length, predicted to be B. aalborgi, and another approximately 10μm in length, predicted to be B. pilosicoli. The former were more common. It is almost impossible to clinically and endoscopically diagnose intestinal spirochetosis, and it is often overlooked histopathologically. Very careful observation is necessary for diagnosis. Severe inflammation is hardly observed with spirochete infection alone. Therefore, when severe inflammation is present, other complications, i.e., amebic colitis should be considered and reevaluated.