Dementia is a syndrome characterised by an appreciable deterioration in cognition resulting in behavioural problems and impairment in the activities of daily living. Decline in cognition is extensive, often affecting multiple domains of intellectual functioning.  
The prevalence of dementia is approximately 1% at the age of 60 years, and doubles every 5 years, to reach 30% to 50% by the age of 85 years.
An estimated 10% to 20% of dementias are caused by potentially reversible conditions; therefore, ruling out these conditions is of the utmost importance when considering a diagnosis of dementia. 
A number of conditions can present in a similar way to dementia syndrome and need to be considered during the evaluation. These include delirium, depression, amnestic syndromes, aphasia, and normal ageing.
Professor of Psychiatry
Case Western Reserve University School of Medicine
RT declares that he has no competing interests.
Dr Rajesh Tampi would like to gratefully acknowledge Dr Sarper Taskiran, Dr Javier Lopez, and Dr Sunanda Muralee, the previous contributors to this monograph. ST, JL, and SM declare that they have no competing interests.
Associate Professor of Psychiatry
Yale School of Medicine
KW declares that she has no competing interests.
Memory Disorders Program
Department of Neurology
University of North Carolina at Chapel Hill
DK has received research support, speaking honoraria, and consulting fees from Eisai, Forest Laboratories, Johnson & Johnson, Medivation, Novartis, Ortho-McNeil, and Pfizer.
Professor Emeritus of Mental Health
University of Aberdeen Institute of Applied Health Sciences
LW declares that he has no competing interests.
Cleveland Clinic Lou Ruvo Center for Brain Health
RS declares that he has no competing interests.
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