Rapidly progressive cerebellar ataxia in West Wales.

Progressive multifocal leucoencephalopathy (PML) is a severe demyelinating disease of the central nervous system that is caused by the JC virus infection. It is often fatal or severely disabling. PML exclusively happens in the context of cell-mediated immunosuppression. Prior to the era of HIV, PML was mainly confined to patients with haematological malignancies and rheumatological diseases. The HIV epidemic in the early eighties led to massive expansion in the incidence and prevalence of the disease. PML has also been recognised to happen due to treatment with monoclonal antibodies such as natalizumab, which is used as a disease-modifying agent for relapsing remitting multiple sclerosis and other monoclonal antibodies used in dermatological and haematological conditions. The clinical picture is that of cognitive decline, visual disturbance and hemiparesis. The correct clinicoradiological picture combined with demonstrating the JC virus DNA in the cerebrospinal fluid (CSF) using PCR (PMR) is enough to establish the diagnosis. Brain biopsy is rarely needed. Immune reconstitution represents the mainstay in the treatment of PML. We present a case of a 47-year-old man who presented with progressive cerebellar ataxia. Investigations confirmed PML. He was found to be HIV positive. We also review the literature.