Epidemiology and risk factors of dementia

Abstract

ementia refers to a syndrome that is characterised by progressive deterioration of cognitive functions.Neuropsychiatric symptoms, such as apathy, agitation, and depression, are also common.With increasing loss of function, a patient is gradually robbed of his or her independence.Eventually, placement in a nursing home may be necessary.Patients with dementia usually survive 7-10 years after onset of symptoms.Dementia places a tremendous burden not only on caregivers, but also on society, and has already been established as one of the major challenges of this century.1 Epidemiology refers to the medical science that studies frequencies of disease. 2 Measures of frequency that are often used in epidemiology are prevalence and incidence.The concept of prevalence refers to the number of patients with a disease at a certain moment in time, whereas measures of incidence reflect the number of new cases over time.Although important for health care planners, the knowledge of frequency of disease in itself is not the goal of epidemiology.Rather, the aim is to gain insight into the mechanisms that cause disease, eventually to be able to cure or prevent disease.Therefore, frequencies are studied in relation to determinants, or risk factors.Although marked as ''the epidemic of our century'', still surprisingly little is known about the epidemiology of dementia.In this chapter, a brief overview will be given of the epidemiology and risk factors of dementia.Furthermore, we comment on some specific methodological problems associated with studies in dementia. SYNDROME AND DISEASE cThe syndrome of dementia may be caused by various underlying diseases, each characterised by a specific constellation of signs and symptoms in combination with a presumed underlying substrate of neuropathology (fig 1).Alzheimer's disease (AD) is the most prevalent cause of dementia.It is a neurodegenerative disorder, generally assumed to be caused by neuritic plaques and neurofibrillary tangles accumulating in the brain.The second most prevalent cause of dementia is vascular dementia (VaD), which may be caused by various types of vascular pathology in the brain, such as ''large vessel'' (large territorial or strategical infarctions) and ''small vessel'' (lacunes and white matter hyperintensities) disease.Other frequent causes of dementia include frontotemporal lobar degeneration and dementia with Lewy bodies.It is often difficult (if not impossible) to reliably distinguish between subtypes of dementia (we will come back to this subject in the section on methodological issues).Therefore, epidemiological studies often focus on dementia as a whole, sometimes giving separate numbers for the two most important subtypes-AD and VaD. PREVALENCEPrevalence is defined as the proportion of a population that has disease at a specific point in time.Prevalence estimates vary highly between studies.These variations may be due to variations in study population-that is, reflect real differences.For example, age is the most important risk factor for dementia.Differences in age between populations will result in different estimates of prevalence.Alternatively, and just as plausible, is the assumption that differences in prevalence estimates are caused by methodological differences, such as study design and diagnostic procedure.One solution to obtain more certainty about the value of prevalence is to combine data from multiple studies in a meta-analysis.Meta-analyses have two advantages.First, small differences due to methodological differences between studies level out.Secondly, and more importantly, the analysis is based on a far larger sample than a single study could ever realise, resulting in more precise estimates. Pooled estimates of prevalenceIn 2000, prevalence data from 11 European population based studies were pooled to obtain stable estimates of prevalence of dementia in the elderly (. 65 years).3 Age standardised prevalence was 6.4% for dementia (all causes), 4.4% for AD, and 1.6% for VaD.Prevalence of dementia was higher v2 www.