# Vascular Cognitive Impairment and Mixed Dementias

## Introduction

Vascular cognitive impairment (VCI) encompasses the full spectrum of cognitive disorders attributable to cerebrovascular disease, from mild vascular cognitive impairment to vascular dementia. It is the second most common cause of dementia after Alzheimer disease and the most preventable form of cognitive decline. In clinical practice, mixed dementia (coexisting vascular and neurodegenerative pathology) is the rule rather than the exception, particularly in older adults.

## Pathophysiology and Mechanisms

### Types of Vascular Brain Injury

Large vessel disease produces strategic infarcts in cognitive networks, affecting structures such as the thalamus, angular gyrus, caudate, hippocampus, and anterior cerebral artery territory. Multi-infarct dementia results from accumulated cortical and subcortical strokes.

Small vessel disease (SVD) is the most common substrate for VCI and manifests in several ways. Lacunar infarcts are small deep infarcts in the basal ganglia, thalamus, internal capsule, and pons. White matter hyperintensities (WMH) involve periventricular and deep white matter and reflect demyelination, axonal loss, and gliosis. Cerebral microbleeds are small hemosiderin deposits reflecting small vessel fragility from either hypertensive or amyloid angiopathy. Enlarged perivascular spaces are visible on MRI in the basal ganglia and centrum semiovale.

Cerebral amyloid angiopathy (CAA) involves amyloid-beta deposition in cortical and leptomeningeal vessel walls, causing lobar hemorrhages, microbleeds, cortical superficial siderosis, and white matter changes. Hypoperfusion, whether global or watershed, produces incomplete white matter infarction from chronic hypoperfusion.

### Mechanistic Pathways

The characteristic dysexecutive cognitive profile results from disruption of frontal-subcortical circuits connecting the prefrontal cortex, caudate, globus pallidus, and thalamus. White matter tract disconnection impairs processing speed and executive function. Blood-brain barrier disruption contributes to chronic inflammation and neurodegeneration, and impaired glymphatic clearance may link vascular disease to amyloid accumulation.

## Clinical Presentation

### Cognitive Profile

Executive dysfunction is the hallmark of VCI, manifesting as impaired planning, organization, mental flexibility, and multitasking. Processing speed reduction with slowed cognitive and motor performance is a characteristic finding, along with difficulty sustaining and dividing attention. Memory impairment is typically a retrieval deficit that improves with cueing, unlike the encoding deficit of AD. Language and visuospatial function are relatively preserved early.

### Associated Features

Gait disturbance is common, presenting as a magnetic gait with short shuffling steps, a wide base, and difficulty initiating gait. Urinary urgency or incontinence, pseudobulbar affect (emotional incontinence), apathy, depression, and motor signs including pyramidal signs and vascular parkinsonism are frequently observed.

### Clinical Course

Post-stroke dementia follows a stepwise decline following clinical strokes, with cognitive decline occurring in 20-30% of stroke survivors within the first year. Subcortical VCI has an insidious, slowly progressive course without distinct stroke events, caused by cumulative small vessel disease. A temporal relationship to stroke events, when present, supports a vascular etiology.

![MRI demonstrating white matter hyperintensities, lacunar infarcts, and microbleeds in cerebral small vessel disease](images/vci-mri-findings.jpg)

## Diagnostic Criteria

### VCI Diagnostic Framework

The diagnosis of VCI requires cognitive impairment demonstrated by neuropsychological testing or clinical assessment, evidence of cerebrovascular disease on neuroimaging (CT or MRI), a reasonable temporal and/or causal relationship between vascular disease and cognitive decline, and exclusion of other causes of cognitive impairment.

### Neuroimaging Assessment

| Fazekas Grade | White Matter Hyperintensities | Clinical Significance |
|---|---|---|
| Grade 0 | Absent | Normal |
| Grade 1 | Punctate foci | Mild; often age-related |
| Grade 2 | Beginning confluence | Moderate SVD; correlates with cognitive slowing |
| Grade 3 | Large confluent areas | Severe SVD; high risk of VCI; gait disturbance |

MRI is preferred over CT for evaluating vascular contributions to cognitive impairment. The STRIVE criteria standardize reporting of SVD markers, including WMH (Fazekas scale), lacunes, microbleeds, perivascular spaces, and brain atrophy. The Fazekas scale grades white matter hyperintensities from Grade 0 (absent) through Grade 1 (punctate foci) and Grade 2 (beginning confluence) to Grade 3 (large confluent areas). Strategic infarct locations, particularly in the thalamus and angular gyrus, can produce cognitive impact disproportionate to lesion size. AD biomarkers (amyloid PET, CSF, plasma) should be considered to evaluate for mixed pathology.

## Mixed Dementias

The coexistence of AD and vascular pathology is the most common form of mixed dementia. Autopsy studies show mixed pathology in 50-60% of dementia cases in individuals over 80. Vascular disease may lower the threshold for clinical expression of AD pathology. Other mixed combinations include DLB plus vascular disease and FTD plus vascular disease. The clinical implication is that treating vascular risk factors may slow decline even when neurodegenerative pathology is present.

## Treatment and Prevention

### Vascular Risk Factor Management

Hypertension is the most modifiable risk factor for VCI, with a target blood pressure of less than 130/80 mmHg. The SPRINT-MIND trial demonstrated that intensive blood pressure control reduced the risk of MCI. Diabetes management requires optimal glycemic control while avoiding hypoglycemia, which independently damages the brain. Statin therapy provides secondary prevention after stroke. Atrial fibrillation requires anticoagulation to reduce stroke risk and likely reduce VCI risk. Smoking cessation reduces stroke and dementia risk. Aerobic exercise improves cerebrovascular health and cognitive function. Mediterranean and MIND diets are associated with reduced dementia risk.

### Pharmacotherapy

Cholinesterase inhibitors provide modest benefit in VCI, particularly in mixed AD-vascular dementia, with donepezil and galantamine having the most evidence. Memantine has limited evidence in VCI but may be considered for moderate-to-severe cases. Antiplatelet therapy is used for secondary stroke prevention, though there is no direct evidence for cognitive benefit independent of stroke prevention. SSRIs are appropriate for post-stroke depression and VCI-associated depression.

### Rehabilitation

Cognitive rehabilitation targeting executive function and processing speed, physical therapy for gait and balance, occupational therapy for functional independence, and speech-language therapy as needed all contribute to management.

![Diagnostic and management algorithm for vascular cognitive impairment](images/vci-management-algorithm.jpg)

![Venn diagram showing overlap of Alzheimer, vascular, and Lewy body pathology in mixed dementia](images/mixed-dementia-venn.jpg)

## Clinical Pearls

Executive dysfunction and processing speed reduction, rather than amnesia, are the cognitive hallmarks of VCI; a patient with a prominent dysexecutive syndrome, gait disturbance, and MRI white matter disease should be evaluated for VCI. Pure vascular dementia is less common than mixed AD-vascular dementia, and AD biomarker testing should be considered in all patients with suspected VCI, particularly those with prominent memory impairment. Hypertension management in midlife is the single most impactful modifiable intervention for reducing VCI risk, as supported by the SPRINT-MIND trial. Strategic single infarcts, especially thalamic and angular gyrus strokes, can cause dementia disproportionate to overall lesion burden, and dementia risk should not be dismissed after a seemingly small stroke. Cerebral amyloid angiopathy should be suspected in patients with VCI, lobar microbleeds, and cortical superficial siderosis on MRI, as it has implications for anticoagulation decisions and anti-amyloid therapy candidacy.

## References

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2. Wardlaw JM, Smith EE, Biessels GJ, et al. Neuroimaging standards for research into small vessel disease and its contribution to ageing and neurodegeneration (STRIVE). *Lancet Neurol*. 2013;12(8):822-838.
3. SPRINT MIND Investigators. Effect of intensive vs standard blood pressure control on probable dementia. *JAMA*. 2019;321(6):553-561.
4. Dichgans M, Leys D. Vascular cognitive impairment. *Circ Res*. 2017;120(3):573-591.