CNS manifestations of vascular dementia often include memory loss, emotional lability (including depression), and executive-task dysfunction. Patients usually have atrial fibrillation or vascular risk factors, including diabetes mellitus, hypertension, hyperlipidemia, obesity, or tobacco use. Patients with previous stroke, coronary artery disease, or peripheral vascular disease are at increased risk.
Vascular dementia is categorized by stroke type:
Embolic infarct. Emboli, typically cardiac in origin, can occlude small or large cerebral arteries, resulting in correspondingly sized infarcts. Atrial fibrillation can promote areas in the atria with relatively low flow turbulence. Blood clots can form that eventually embolize via the carotid arteries. Multiple emboli can occur, causing progressive dementia.
Cerebral hemorrhage —small or large—can be devastating. Hypertension is the major risk factor for this form of stroke.
Multi-infarct dementia. Multiple cerebral blood vessel infarcts classically lead to stepwise functional decline after each event. Multiple small infarcts can occur in various brain regions, including the cortex and basal ganglia. Binswanger’s disease, a variant of vascular dementia in which incomplete ischemia is limited to the hemispheric white matter, tends to be fairly progressive.2
Small-vessel disease. Reduced blood flow and tissue perfusion can cause small-vessel disease. Often the ischemia is “silent,” detectable only on MRI or CT. The infarcts typically cause lacunar lesions, nerve demyelination, and gliosis.3 These can occur to some extent in nondemented patients but become significant with more-extensive disease.
FEATURES OF LEWY BODY DEMENTIA
As with all dementias, permanent memory loss must be present to diagnose this dementia sub-type. Overall cognitive deficits may be more prominent than memory loss, however. The patient may have trouble performing cognitive tasks that employ visuospatial abilities, executive functions, and attention. Neuropsychiatric symptoms that overlap with Alzheimer’s dementia include apathy, anxiety, agitation, depression, anhedonia, and paranoia.
The presence of visual hallucinations, fluctuating cognition, or extrapyramidal symptoms (EPS) distinguish Lewy body from Alzheimer’s dementia.
Visual hallucinations are prominent in Lewy body dementia and often prompt psychiatric referral (Table 2). They usually surface early in the disease course and tend to persist. Other sensory hallucinations also can occur.
The hallucinations often are detailed and vivid and the patient may be aware they are occurring, especially if the dementia is not advanced. Treatment might not be necessary for mild hallucinations, which can concern the caregiver more than the patient.
Antipsychotics paradoxically worsen hallucinations in Lewy body dementia, and many patients present to psychiatrists after failing an empiric trial. A failed antipsychotic course in a patient diagnosed with Alzheimer’s dementia could indicate that the diagnosis is incorrect.
Fluctuating cognition occurs in 50% to 75% of Lewy body cases. Alertness, attention, and concentration are variable and can cycle within hours to weeks. The patient often is fairly interactive and social for a time, then has periods of diminished function and being “out of it.” Some patients have recurrent delirium and undergo multiple workups in search of a cause.
EPS. As many as 75% of Lewy body patients have parkinsonian motor features.4 Because these features are not essential to the diagnosis, their absence is the most common reason Lewy body dementia goes unrecognized.1
Motor involvement varies and can be worsened by antipsychotics. Overuse of antipsychotics in Alzheimer’s or vascular dementia also can cause motor symptoms that mimic Lewy body features.
EPS orientation tends to be axial, showing less facial expressivity and more postural imbalance. Peripheral signs such as tremor and extremity rigidity tend to be less dominant.
MAKING THE DIAGNOSIS
Vascular and Lewy body dementia diagnoses are primarily based on clinical features and findings. Memory loss is necessary for either diagnosis.
Vascular dementia. Most consensus criteria require presence of dementia, physical or radiologic signs of a stroke, and a temporal relationship between the stroke and the dementia for a vascular dementia diagnosis.
Hachinski’s “ischemia scale” can help differentiate multi-infarct from Alzheimer’s dementia.5 Cases are scored on a 0-to-9 scale, with point values for abrupt onset; stepwise course; history of stroke; and presence of somatic complaints, emotional lability, hypertension, and focal neurologic signs. A score ≥4 suggests vascular dementia.
The scale, however, does not account for imaging studies, vascular risk factors other than hypertension, or repeated silent strokes that can cause symptoms. Also, some patients who score below the cutoff have strategic infarct dementias.
Lewy body dementia. Clinical consensus guidelines developed by McKeith et al6 can help clinicians recognize and categorize this dementia type (Table 2). Several studies of diagnostic criteria have shown very good specificity but variable sensitivity.7 Because no standard imaging modalities or serum markers exist, presence of progressive memory loss, fluctuating cognition, visual hallucinations, and EPS should drive the diagnosis.