Progressive multifocal leukoencephalopathy mimicking a cerebral vasculitis flare

Introduction: Progressive multifocal leukoencephalopathy (PML) is a rare opportunistic infection caused by reactivation of the John Cunningham (JC) virus in immunocompromised patients and may present with focal neurological deficits that mimic stroke.
Case Presentation: 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 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 had been administered at the time of her diagnosis two years prior.
Initial imaging on non-contrast computed tomography (CT) of the 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 in the left frontal and left parietal lobes suggestive of progressive multifocal leukoencephalopathy (PML). A magnetic resonance imaging (MRI) scan of the brain conducted three months earlier had been unremarkable. Cerebrospinal fluid (CSF) polymerase chain reaction (PCR) testing confirmed the presence of polyoma John Cunningham (JC) virus deoxyribonucleic acid (DNA).
Conclusion: This case highlights that progressive multifocal leukoencephalopathy should be considered an important differential diagnosis in immunocompromised patients presenting with new stroke-like features.