RESUMEN
A case of pathologically confirmed progressive multifocal leucoencephalopathy presenting with unilateral parkinsonism and cognitive decline that significantly improved over a 12-month period without any treatment is described. The patient had a background of chronic lymphocytic leukaemia, but had been in complete remission for 4 years at the time of diagnosis. This case is highly unusual not only in terms of the mode of clinical presentation in an apparently immunocompetent patient but also in that the patient spontaneously improved without any intervention. Progressive multifocal leucoencephalopathy should therefore be considered in the differential diagnosis of movement disorders developing in patients with a history of lymphoproliferative disease, even if they are in remission. Furthermore, such cases may not always require treatment, as the patient's immune system may overcome the viral disease process with spontaneous resolution of their neurological disorder.