D'Arcy L. Little, MD*
Anu Kumar, MD**
*Chief Resident, Family Medicine. Sunnybrook Health Science Centre, North York, Ontario
**Radiology Resident, Mount Sinai Hospital, Toronto, Ontario
As our society ages, dementia increases in prevalence. Although uncommon before age fifty, it is estimated that 10% of those over age 65 years, and up to 40% of those over age 85 years suffer from a type of dementia. Although there are over 70 different causes of dementia, Alzheimer's Disease (AD) is the most common type (See Table 1) . Some conditions that cause dementia can be treated and this can alleviate or occasionally resolve the dementia. As a result, patients with cognitive impairment should undergo appropriate investigation to assess any potential for reversibility.
Alzheimer's Disease is a progressive neurodegenerative disease with characteristic clinical and pathological features. A definitive diagnosis of AD requires the analysis of brain tissue, usually at autopsy, looking for the classic features of cortical atrophy, synaptic and neuronal loss, amyloid angiopathy, neuritic plaques with an amyloid core, neurofibrillary tangles with paired helical filaments, and localized inflammatory reaction. However, the combination of clinical features, and appropriate laboratory and/or radiologic techniques results in a diagnostic accuracy of approximately 80 percent.