What is the difference between dementia and Alzheimer's disease?

Dementia vs. Alzheimer's Disease: Understanding the Relationship

Dementia is a clinical syndrome characterized by progressive cognitive decline that interferes with daily functioning, while Alzheimer's disease is the specific underlying pathological process that causes approximately 60-80% of dementia cases. 1

Dementia: The Umbrella Term

Dementia represents a syndrome, not a specific disease, defined by:

• Progressive cognitive impairment affecting memory, reasoning, language, visuospatial abilities, or executive function that significantly interferes with work or usual daily activities 1
• Multiple potential causes including Alzheimer's disease, vascular disease, Lewy body disease, frontotemporal degeneration, or combinations of these pathologies 1
• A clinical diagnosis based on documented decline in cognitive function from a previous level of performance, obtained through patient history and knowledgeable informant reports 1

The key distinction is that dementia describes what you observe clinically—the symptoms and functional impairment—without specifying the underlying cause 2.

Alzheimer's Disease: A Specific Cause

Alzheimer's disease refers to:

• A specific pathophysiological process characterized by accumulation of beta-amyloid plaques and hyperphosphorylated tau protein tangles in the brain, leading to neuronal loss and brain atrophy 1, 3
• The most common etiology of dementia, though dementia is thought to be most commonly caused by Alzheimer's disease, with multiple etiologies often coexisting 1
• A disease that exists across a clinical spectrum from preclinical (no symptoms) to mild cognitive impairment to dementia stages 1, 4

Alzheimer's disease dementia specifically refers to the clinical syndrome that arises as a consequence of the Alzheimer's disease pathophysiological process 1.

Critical Clinical Distinctions

When Dementia is NOT Alzheimer's Disease

The diagnosis of probable Alzheimer's disease dementia should not be applied when there is evidence of: 1

• Substantial cerebrovascular disease (stroke temporally related to cognitive decline, multiple infarcts, severe white matter disease)
• Core features of Dementia with Lewy bodies (visual hallucinations, parkinsonism, REM sleep behavior disorder)
• Prominent features of frontotemporal dementia (early behavioral changes, language-predominant presentations)
• Other active neurological diseases or medical conditions affecting cognition

The Overlap Problem

Pure Alzheimer's disease pathology is uncommon—most older adults with dementia have multiple neuropathological markers contributing to their cognitive decline 1. This means:

• Vascular pathology frequently coexists with Alzheimer's pathology 1
• A physician should not let evidence of one dementia type preclude assessment for other pathologies 1
• The degree of frailty influences whether someone with Alzheimer's pathology will meet clinical criteria for dementia 1

Practical Clinical Framework

For Diagnosis

1. First, establish that dementia is present by documenting cognitive decline that significantly interferes with daily function 1

2. Then, determine the likely etiology through: 1, 5

   • Detailed history from patient and informant about onset pattern (gradual vs. sudden)
   • Cognitive domain assessment (memory-predominant vs. language vs. visuospatial vs. executive)
   • Neurological examination to identify features of other conditions
   • Neuroimaging to exclude vascular or structural causes
   • Laboratory tests to rule out reversible causes

3. Consider biomarker confirmation when diagnostic uncertainty exists, particularly with emerging disease-modifying therapies that target Alzheimer's pathology specifically 1, 5

Common Pitfall to Avoid

Do not assume all dementia is Alzheimer's disease—approximately 31-74% of patients with symptomatic Alzheimer's disease are not properly identified in primary care settings, and even among specialists, the etiological diagnosis changes in 36% of patients following advanced biomarker testing 5. The heterogeneity of dementia causes requires careful differential diagnosis, as different etiologies require different treatments and have different prognoses 1.