What is Dementia?
Dementia is a chronic acquired syndrome defined by significant impairment in at least two cognitive domains—including memory, language, executive function, visuospatial abilities, or behavior—that represents a decline from previous functioning and interferes with independence in daily activities. 1
Core Defining Features
Dementia requires all of the following diagnostic elements 1:
- Cognitive or behavioral symptoms that interfere with work ability or usual activities
- Documented decline from a previous level of performance and functioning
- Not explained by delirium or major psychiatric disorder
- Objective confirmation through clinical history from both patient and a reliable informant, plus formal cognitive assessment 1, 2
The impairment must involve at least two of these specific domains 1:
- Ability to acquire and remember new information
- Reasoning and judgment
- Visuospatial abilities
- Language function
- Personality or behavioral changes
Epidemiology and Impact
Dementia affects 47 million people worldwide, with projections reaching 131 million by 2050 1, 3. In the United States, prevalence is 15% in adults over 68 years, making it the fifth leading cause of death in those over 65 1. The condition invariably progresses to complete dependence and death 1.
Common Etiologies
Alzheimer disease accounts for 50-70% of dementia cases, making it the most common cause 1. Other major etiologies include 1:
- Frontotemporal dementia (FTD) - characterized by personality changes, impaired judgment, and language disturbances with notably preserved memory 4
- Dementia with Lewy bodies (DLB) - involves visual hallucinations and parkinsonism 1
- Vascular dementia (VaD) - results from cerebrovascular disease and stroke 1
- Mixed dementias - most commonly Alzheimer disease combined with cerebrovascular pathology 3
Less common causes include normal pressure hydrocephalus, rapidly progressive dementias from prion diseases, infectious/inflammatory conditions, neoplastic disorders, and toxic/metabolic conditions 1.
Distinction from Mild Cognitive Impairment
Mild cognitive impairment (MCI) differs from dementia in that cognitive deficits are mild and cause minimal interference with daily functioning, whereas dementia requires significant functional impairment 1. MCI represents a symptomatic predementia phase, particularly for Alzheimer disease 1.
Clinical Progression
Dementia progresses through three severity stages 1:
- Early dementia: Memory loss and disorientation predominate
- Mild to moderate dementia: Marked loss of instrumental activities of daily living
- Severe dementia: Marked communication difficulties with complete reliance on others for basic activities
Pathophysiology
The syndrome results from brain disease or injury causing neuronal degeneration 1, 5. Multiple pathologies commonly contribute to any individual patient's dementia, with Alzheimer pathology frequently coexisting with cerebrovascular disease 3, 5. Age is the strongest risk factor, with additional contributions from genetic factors (apolipoprotein ε4, family history), cardiovascular risk factors (hypertension), and lifestyle factors (low education, head trauma) 1.
Functional Consequences
Weight loss beginning before diagnosis is a prominent clinical feature, creating a vicious cycle where dementia leads to decreased food and fluid intake, which accelerates cognitive decline 1. Patients progressively lose ability to perform self-care, self-maintenance, and complex tasks like managing finances 6. Behavioral and psychological symptoms commonly develop, causing significant distress to patients and caregivers 7.