Streptococcus agalactiaeによる孤立性三尖弁感染性心内膜炎の1例

Isolated Tricuspid Valve Infective Endocarditis Caused by Streptococcus agalactiae

　患者は49歳，男性，会社事務員．心疾患の既往はなく，薬物乱用歴もない．発症に先行して歯科的処置も受けていない．1997年7月下旬から40℃を越える発熱があり，近医で抗生剤を処方された．一時的に解熱したものの発熱を繰り返すため，9月8日精査加療目的で当院へ入院した．入院後の血液培養でStreptococcus agalactiae（以下S. agalactiae）が検出され，心エコー検査で三尖弁後尖に25×17mm大の疣贅を認め，感染性心内膜炎（以下I. E.）と診断した．3週間以上抗生剤治療を継続したが，炎症反応が遷延した．起因菌が侵襲性の強いS. agalactiaeであることも考慮し，手術適応と判断し，10月6日三尖弁疣贅切除・三尖弁形成術を施行した．術後経過は良好である．特に誘因なく，健常成人に孤立性三尖弁I. E. が発症することは稀であり，かつS. agalactiaeを起因菌とするI. E. も少なく，極めて稀な症例と思われ報告する．

　Isolated tricuspid valve infective endocarditis caused by Streptococcus agalactiae is an uncommon disease. We describe herein a healthy adult who suffered from this disease. A previously healthy 49-year-old male was admitted to our hospital with a six week history of remittent fever, although an oral cephalosporin had been administered. There was no previous cardiac history. He had never received any dental procedure. He denied drug abuse. Cultures of two blood samples yielded Streptococcus agalactiae. Transthoracic and transesophageal echocardiography demonstrated a large vegetation (25mm × 17mm) attached to the posterior cusp of the tricuspid valve with moderate regurgitation. A diagnosis of tricuspid valve infective endocarditis was made and he was treated with antibiotics for more than three weeks. But the infection was difficult to control with antibiotics alone. Streptococcus agalactiae is very virulent and early operation is recommended if there is evidence of uncontrollable infection. Urgent tricuspid valvuloplasty was performed. The postoperative course was uneventful and he is doing well at the time of follow-up.