Case of fingolimod‐associated progressive multifocal leukoencephalopathy in multiple sclerosis

Abstract Background Fingolimod is associated with an increased risk of developing progressive multifocal leukoencephalopathy (PML). Case Presentation We report a 63‐year‐old woman with severe clinical decline (Expanded Disability Status Scale increasing from 3.5 to 7.0). She started fingolimod 0.5 mg/day at the age of 51 years in the FTY720 trial in Japan, and has been taking it orally ever since. Brain magnetic resonance imaging showed abnormal signals from the subcortical region to the deep white matter, mainly in the right frontal lobe. No gadolinium‐enhancing lesions were observed, and diffusion‐weighted imaging showed marginal hyperintense and central hypointense signals; the characteristic findings in PML. We found her cerebrospinal fluid was positive for John Cunningham polyomavirus DNA, and the diagnosis of PML was made. We administered several steroid pulses in case of immune reconstitution inflammatory syndrome. The progression of symptoms and the enlargement of magnetic resonance imaging lesions stopped after 3 months. Conclusions This case shows that PML should always be kept in mind as a side‐effect of disease‐modifying therapy for multiple sclerosis.