Progressive multifocal leukoencephalopathy in a patient with Franklin disease and hypogammaglobulinemia

We report an association between histologically confirmed progressive multifocal leukoencephalopathy (PML) and an extremely rare humoral immunodeficiency disease, Franklin disease. In our patient, clinical presentation has been typical and prompted us, together with radiological findings, to perform a brain biopsy to confirm the diagnosis even if there was no evidence of any other risk factor except hypogammaglobulinemia. We suggest that PML should be suspected in patients in whom immunosuppression is not obvious (i.e. not only in the setting of HIV infection or disseminated end-stage lymphomas) and involves defects in humoral immunity.