Progressive Multifocal Leukoencephalopathy Mimicking a Cerebral Vasculitis Flare.

We report a case of a 68-year-old woman with a background of primary cerebral vasculitis, which was diagnosed two years ago. She appeared to have had a recurrence of her symptoms with new onset history of expressive dysphasia, right-sided upper limb weakness, and right-sided facial weakness during a rheumatology clinic visit. The patient was on maintenance azathioprine for her cerebral vasculitis at the time of presentation. She had received a total of 2 g of rituximab through intravenous infusion, with a two-week interval between doses. Additionally, she had undergone intravenous cyclophosphamide treatment (15 mg/kg) following the standard vasculitis regimen for induction remission therapy, which was administered at the time of her diagnosis two years prior. Initial imaging on non-contrast computed tomography head after admission to the emergency department did not show any acute neurological findings. Further imaging studies revealed changes in the right parietotemporal white matter T2 hyperintensity with similar changes on the left frontal and left parietal lobes suggestive of progressive multifocal leukoencephalopathy (PML). A magnetic resonance imaging (MRI) of the brain conducted three months prior was found to be unremarkable. Cerebrospinal fluid (CSF) polymerase chain reaction (PCR) testing confirmed the presence of polyoma John Cunningham (JC) virus deoxyribonucleic acid (DNA). This case highlights that PML should be an important differential to consider in any immunocompromised patient who presents with new stroke-like features.