A Case Report of Progressive Multifocal Leukoencephalopathy (PML) in an Immunocompetent Patient.

Progressive multifocal leukoencephalopathy (PML) is a rare but fatal demyelinating disorder resulting from reactivation of latent John Cunningham virus (JCV), which induces demyelinating lytic infection of oligodendrocytes. We report a case of PML in an individual without identifiable immunodeficiency who presented with insidious and progressive deficits in speech and motor function. Diagnostic workup revealed JC viral DNA in cerebrospinal fluid, and magnetic resonance imaging (MRI) demonstrated multiple asymmetric lesions within the subcortical and deep white matter. Despite administration of the immune checkpoint inhibitor pembrolizumab, the patient's neurological status continued to decline, culminating in death. This case underscores the necessity of considering PML in the differential diagnosis of patients lacking classic risk factors when clinical presentation and neuroimaging findings are indicative of demyelinating pathology.