Successful treatment of progressive multifocal leukoencephalopathy with mirtazapine and mefloquine in refractory myeloma

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We herein describe a 52-year-old man with multiple myeloma (MM) who developed progressive multifocal leukoencephalopathy (PML). He was diagnosed with MM in December 20XY, and underwent high-dose chemotherapy followed by autologous stem cell transplantation. He relapsed in October 20XY+2, and he was treated with the oral administration of cyclophosphamide and prednisolone (CP). He developed apraxia and visual disturbance in March 20XY+4. Since PML was suspected, we stopped CP and mirtazapine was initiated; however, his neurological symptoms did not improve. He was diagnosed with PML based on John Cunningham virus (JCV) DNA in his cerebrospinal fluid (CSF). He was treated with therapy involving of mirtazapine, cytarabine, and high-dose immunoglobulin; however, his neurological disorders did not improve despite the disappearance of JCV DNA in his CSF. Therefore, we started combination therapy of mirtazapine and mefloquine, which resulted in the ­significant improvement of both his neurological symptoms and MRI findings. Although we restarted the anti-MM treatment, his neurological symptoms remained stable for more than 2 years with the continuation of this com­bination therapy. The present case suggests that combination therapy of mirtazapine and mefloquine is effective for patients with PML, particularly those requiring immunosuppressive chemotherapy.