Progressive Multifocal Leukoencephalopathy (PML) is a rare and severe viral infection affecting the central nervous system. PML is caused by the JC virus, which attacks the oligodendrocytes- cells responsible for forming the protective coating around nerves. The condition is progressive and can cause severe disability or even death. Synonyms for PML include progressive multifocal leukoencephalitis, progressive multifocal demyelinating leukoencephalopathy, and multifocal leukodystrophy. These terms refer to the same condition and are used interchangeably. While there is no known cure for PML, treatment focuses on managing symptoms and improving quality of life.