The Canadian Review of Alzheimer's Disease and Other Dementias @bullet 17 Relationships between Dementia and Depression

Dementia increases with age, with an overall prevalence in Canada of 8% in those 65 years and older, 2.4% in those aged 65 to 74 years, 11.1% in those aged 75 to 84 years, and 34.5% in those aged 85 years and older.1 Alzheimer’s disease (AD) is thought to be the most common type of dementia in all age groups. How ever, younger age groups are more likely than older age groups to be diagnosed with other dementias, such as frontotemporal dementia and vascular dementia.2 Major depressive disorder is also common, but is only one of a number of disorders listed in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)3 with prominent depressive symptoms (Table 1).3 These include dysthymic disorder, depressive epi sodes of a bipolar disorder, mood disorders secondary to a medical disorder (such as hypothyroidism), mood disorders secondary to a substance, adjustment disorders and bereavement. Depressive disorder is commonly seen in all stages of adult life and, while its prevalence is slightly lower in the elderly,4 its sequelae are probably greater in more frail people, exerting a more deleterious effect on functional abilities and even increasing the length of stay for hospitalizations related to primary medical conditions.5 Depressive disorder in seniors can occur as part of a lifelong recurrent disorder, or it can present for the first time in old age. It is frequently concurrent with other medical and mental disorders, including various dementias.