Neuropathological evaluation of mixed dementia

Area of Science:

• Neurology
• Pathology
• Gerontology

Background:

• Mixed dementia (MD) involves co-occurring Alzheimer disease (AD) and vascular encephalopathy, with controversial diagnostic distinctions.
• Current criteria for MD use clinical/neuroimaging findings of AD and cerebrovascular disease (CVD), but causal links remain unclear.
• Proposed diagnostic criteria for MD combine autopsy-proven AD with significant vascular or ischemic brain lesions.

Purpose of the Study:

• To investigate the prevalence and pathological characteristics of mixed dementia (MD).
• To evaluate the coexistence of Alzheimer disease (AD) and cerebrovascular lesions in elderly demented subjects.
• To discuss the pathogenic factors and diagnostic limitations in differentiating AD, vascular dementia (VaD), and MD.

Main Methods:

• Retrospective and prospective autopsy studies were conducted on demented elderly subjects.
• Analysis included a series of 1500 demented individuals, with 830 having clinically probable AD.
• Histopathological examination assessed AD, vascular lesions, and other dementing pathologies.

Main Results:

• Mixed dementia (MD) prevalence in autopsy studies ranged from 2% to 58% (mean 6-12%).
• In a Vienna series, MD was diagnosed in 2.4-4.6% of cases, while pure AD was 41.5-52.0% and pure VaD was 2.0-11%.
• Vascular lesions were common in AD and VaD (subcortical/microinfarcts), but large/hemispheral infarcts were more frequent in MD, suggesting distinct pathogenetic mechanisms.

Conclusions:

• Alzheimer disease (AD) and cerebrovascular lesions frequently coexist in cognitively impaired patients.
• Distinct pathological patterns in AD, VaD, and MD suggest different underlying pathogenic mechanisms.
• Current clinico-pathological criteria for diagnosing VaD and MD are insufficient, necessitating development of validated histopathological criteria.