Progressive multifocal leucoencephalopathy associated with lupus and methotrexate overdose.

Progressive multifocal leucoencephalopathy (PML) is a CNS infection of oligodendrocytes by JC virus, which rarely occurs in lupus, and can be mistaken for antiphospholipid antibody syndrome or neuropsychiatric systemic lupus erythematosus (NSLE). This case of PML in a patient with systemic lupus erythematosus on supra-therapeutic doses of methotrexate emphasises that CNS infection is an important diagnostic consideration before empiric treatment with immunosuppresants for NSLE.