Early onset dementia.

Dementia is characterized by a decline in cognitive faculties and occurrence of behavioral abnormalities which interfere with an individual's activities of daily living. Dementing disorders usually affect elderly individuals but may occur in individuals younger than 65 years (early-onset dementia or EOD). EOD is often misdiagnosed or its diagnosis is delayed due to the fact that it has a more varied differential diagnosis than late-onset dementia. EOD affects individuals at the height of their career and productivity and produces devastating consequences and financial loss for the patient's family as well as society. EOD is not uncommon and is diagnosed in up to a third of patients presenting with dementia. Most importantly, some of the causes of EOD are curable which makes the need for a specific and timely diagnosis crucial. The present chapter presents a systematic approach to the differential diagnosis of EOD and provides readers with the clinical and neuroimaging features of these disorders as well as important considerations for their diagnostic evaluation. Specifically, the nuances of assessing the history and examination are discussed with careful attention to the various methods of cognitive and behavioral evaluation. A step-wise approach to diagnostic testing is followed by a discussion of anatomical localization, which often aids in identifying specific etiologies. Finally, in order to organize the subject for the reader, the various etiologies are grouped under the general categories of vascular, infectious, toxic-metabolic, immune-mediated, neoplastic/metastatic, and neurodegenerative.