Diagnosis of vascular dementia and Alzheimer's disease.

Vascular dementia (VaD) and Alzheimer's disease are sometimes difficult to distinguish due to overlaps in symptomatology, pathophysiology and comorbidity. The issue of differential diagnosis is further complicated by the fact that many patients have concomitant Alzheimer's disease and cerebrovascular disease (CVD) ('mixed' dementia). Each pathology may contribute to varying degrees, giving rise to a continuum of patients in whom pure CVD and pure Alzheimer's disease represent the two extremes. Despite the clear overlap between the conditions, and the prevalence of 'mixed' dementia, a number of criteria for Alzheimer's disease and VaD do not make provision for 'mixed' dementia distinct from the coincidence of any two other dementing illnesses. We will discuss the current diagnostic criteria for VaD, with or without coexisting Alzheimer's disease, in an effort to determine how best to diagnose VaD. These include traditional criteria such as the Diagnostic and Statistical Manual of Mental Disorders or the Hachinski Ischemic Scale, and the more recently developed criteria by the California Alzheimer's Disease Diagnostic and Treatment Centers (CAD-DTC) and the National Institute of Neurological Disorders and Stroke and the Association Internationale pour la Recherche et l'Enseignement en Neurosciences (NINDS-AIREN) International Workshop. The CAD-DTC and NINDS-AIREN rely on neuroimaging--ideally, every patient suspected of dementia should have brain imaging, but although this is possible in clinical trials (for which these criteria were designed), it is not always feasible in population-based epidemiological studies and clinical practice in some countries.