Progressive multifocal leukoencephalopathy in a 44-year old male with idiopathic CD4+ T-lymphocytopenia treated with mirtazapine and mefloquine.

Progressive multifocal leukoencephalopathy (PML) is an opportunistic viral infection of the central nervous system caused by the reactivation of John Cunningham virus (JCV) in immunocompromised patients, most commonly in human immunodeficiency virus (HIV) infection, and less commonly in those receiving various immunosuppressive regimens. Prognosis of untreated PML is grave and the mainstay of treatment is the reversal of immunosuppression, usually by institution of antiretroviral drugs in HIV patients and cessation of immunosuppressive therapies in others. PML is increasingly being reported in those with minimal or occult immunosuppression. A small fraction of these patients meet the criteria for idiopathic CD4+ T-lymphocytopenia (ICL) after exclusion of all secondary causes of lymphocytopenia, including HIV. A 44-year-old previously healthy male presented with clinical and radiological features suggestive of PML. Cerebrospinal fluid samples were repeatedly negative for JCV. Immunohistochemistry on brain biopsy eventually confirmed PML. Despite extensive work-up, the only abnormality detected was an unexplained and persistently low absolute CD4+ T-lymphocyte count. Based on the limited available literature on the treatment of non-HIV PML, he was treated with a combination of mirtazapine and mefloquine with clinical improvement. Non-HIV PML remains relatively uncommon, and PML as a presenting feature of ICL is rare. It is important to document and follow these patients to be able to assess the relative risks associated with various causes and formulate effective therapeutic strategies.