多発皮膚病変を伴うBalamuthia mandrillaris による肉芽腫性脳炎の症例

抄録

Balamuthia mandrillaris is one of the free-living amoebae that causes potentially fatal cutaneous and central nervous system infection. Both the diagnosis and treatment are challenging, especially when the central nervous system is involved. Herein, we report a case of granulomatous amoebic encephalitis caused by B. mandrillaris, in a patient who presented with subcutaneous lesions. A 55-year-old patient with a history of ANCA-associated vasculitis who was on maintenance dialysis was referred to our hospital for investigation and treatment of an intracranial lesion. He had had multiple subcutaneous nodules for nine months before the referral, which had been histopathologically diagnosed about a month prior to the referral as granulomatosis with polyangiitis. Brain MRI showed a space-occupying lesion with surrounding edema in the left occipital lobe. Brain biopsy was performed, and the histopathological diagnosis was epithelioid cell granuloma； no pathogen could be identified. Suspecting either deterioration of granulomatosis with polyangiitis or infection, the patient was started on treatment with a corticosteroid and several antibiotics, antifungal, and antiprotozoal agents. However, the intracranial lesion continued to progress despite all the treatment, and the patient died on the 33rd hospital day. Further investigation at the National Institute of Infectious Diseases revealed B. mandrillaris infection in both the subcutaneous and intracranial lesions. From our experience of this case, we suggest that B. mandrillaris infection be included in the differential diagnosis in patients presenting with cutaneous granulomatous lesions of unknown cause； early diagnosis, before the amoeba invades the central nervous system, is of critical importance.