A Rare Case of Cerebellar Progressive Multifocal Leukoencephalopathy due to Idiopathic CD4 Lymphocytopenia.

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disorder caused by reactivation of JC virus during a time of cell mediated immune suppression. One potential rare cause of PML is Idiopathic CD4 lymphocytopenia (ICL) in which there is an unexplained deficit of CD4 T cells. We present a case of cerebellar PML in the absence of known immunosuppression leading to the diagnosis of ICL.