Late-Onset Combined Immunodeficiency presenting with Progressive Multifocal Leukoencephalopathy and associated Immune Reconstitution Inflammatory Syndrome.

Progressive multifocal leukoencephalopathy (PML) can rarely occur in individuals with occult immunosuppression. Here, we describe the case of an adult man who presented with PML, in whom CD4+ lymphocytopenia and hypogammaglobulinemia were subsequently identified, leading to a diagnosis of late-onset combined immunodeficiency. Intravenous immunoglobulin replacement therapy was initiated. His clinical course, though complicated by immune reconstitution inflammatory syndrome, was favorable.