Progressive multifocal leukoencephalopathy presenting with bilateral myoclonus: a case report

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of the central nervous system (CNS) caused by John Cunningham virus lytic infection of the oligodendrocytes, the myelin-producing cells in the CNS. Symptoms largely vary depending on location and size of the lesions, and the most frequent clinical presentation is characterized by motor deficits, altered consciousness, gait ataxia, and visual symptoms. Despite limb weakness or hemiparesis as the most frequent presenting symptom, involuntary movement is far less common, and very few cases are described in the literature with focal movement disorders without additional neurologic abnormalities. Here we described a case of PML in a patient treated for non-Hodgkin lymphoma with immunomodulatory chemotherapies who presented with bilateral myoclonus of the upper limbs. This report highlights the importance of considering PML in the differential diagnosis of focal movement disorders and discusses the potential causative mechanism of this atypical presentation.