脳のhistoplasmosis

Central Nervous System Histoplasmosis

はじめに

　輸入真菌症は，患者がある特定の地域を訪れた際，その地域でのみ生息している真菌に感染し，（帰国後）発症したものをさす。近年，注目されている輸入真菌症の1つにヒストプラズマ症がある。ヒストプラズマ症はわが国で急激に患者数が増加していると報告されている^1，2）。特徴としては健常人に感染しうることが挙げられ（高病原性），わが国土着の深在性真菌症で通常みられるような日和見感染とは性質が異なることに留意すべきである。またヒストプラズマ症は呼吸器系の障害が多いが，頻度は少ないものの脳神経系へ波及し，しばしばその診断が困難である。本稿では中枢神経系ヒストプラズマ症（central nervous system histoplasmosis: CNSヒストプラズマ症）について概説し，診断に難渋した自験例を呈示する。

Abstract

　Central nervous system (CNS) histoplasmosis is one of the important endemic mycoses in America and Africa.　Although the incidence of CNS histplasmosis in non-endemic areas is increasing,the diagnosis of isolated CNS histoplasmosis in these areas remains challenging.　Since the diagnosis is often missed,the outcome of CNS histoplasmosis is occasionally poor.　One of the important complications of this condition is hydrocephalus,which may be identified before meningitis is diagnosed.　Antigen or serological tests are useful for the diagnosis of CNS histoplasmosis; however,it should be noted that false positive results may be obtained because of cross reactions due to infections by other fungi.　Further,repeated culture with a large volume of cerebrospinal fluid is essential because of the low sensitivity of culture.　Thus,it is recommended that tests for CNS histplasmosis be repeated,even if negative results are obtained initially.　Liposomal amphotericin B is the usual initial therapy for CNS histoplasmosis.　However,the rate of failure of initial treatment is high and relapse can occur in the next few years,which calls for careful management of patients with CNS histoplasmosis.　Continued therapy with antifungal agents such as fluconazole or itraconazole is often required.　We report a case of a patient with chronic meningitis in whom the tests for other causes were negative for about 10 years,and who was eventually diagnosed with CNS histoplasmosis.　Treatment with fluconazole was initiated,and the patient's symptoms gradually improved.　Further cerebrospinal fluid (CSF) analysis and brain computed tomography (CT) during the follow-up period of 2 years and 9 months did not reveal recurrence of meningitis or hydrocephalus,thereby indicating the successful treatment of CNS histoplasmosis with fluconazole.　CNS histoplasmosis should always be included in the differential diagnoses of chronic meningitis in non-endemic areas even in the case of immunocompetent individuals.