Susham Gupta is a specialist registrar in old age psychiatry, working for the Central and North West London NHS Foundation Trust. He is in his fourth year as a dual specialty trainee. Olivia Fiertag is a specialist trainee with West London Mental Health NHS Trust. James Warner is a consultant psychiatrist with Central and North West London NHS Foundation Trust.
Correspondence: Correspondence Dr Susham Gupta, Nightingale House, St Charles Hospital, Exmoor Street, London W10 6DZ, UK. Email: sushamgupta{at}nhs.net
Over 95% of cases of dementia are attributable to Alzheimers disease, vascular, Lewy body and fronto-temporal dementia, and a few other common causes. In this article we consider some of the rare and unusual causes that account for the remaining 5%. Categorising them according to aetiological group (degenerative, vascular and infectious causes, and human prion diseases), we discuss the presentation of these forms and reasons for variations in estimated prevalence rates in the general population.