Teaching Sessions

Abstract

Alzheimer's disease (AD), vascular dementias (VaD), Lewy body dementias, and frontotemporal dementia all have a complex presentation and challenges in the diagnostic criteria make none of these 'causes' truly correct. It is more instructive to see these entities on a continuum of neuropathological conditions.By example, the DSM-IV criteria do not do justice to the variety of syndromes seen in AD. The specific wordings of the criteria leave much room for interpretation. These criteria require impairment of function; if memory impairment or another symptom is not severe enough to demonstrate functional impairment in activities of daily living, the diagnosis should not be dementia. Diagnostic criteria disregard mixed cases and are mostly useful for research criteria only, not epidemiological field work. Clearly, it is difficult regarding who to count.Nevertheless, the non-genetic risk factors based on epidemiological studies showed that in AD, age is the single most important factor. The prevalence increases with age, at about two-fold for every 5 years in patients aged >65 years; this means by 85 years of age, the prevalence is ~20%, at 90, at ~40%. Beyond 90 years, there is little data. When genetic considerations are taken into account, these data may be relevant to finding individuals who are "coded" to survive.What happens to an individual when they are young can also affect their risk of dementia later in life. Head trauma with concomitant short-duration coma (3-4 days) seems to confer a small increased risk. This injury may cause a low-level effect that may remain active over decades; however, the underlying processes are not understood.Another risk factor is a low education level. Several studies have demonstrated that higher education (versus no schooling) confers a protection of 10 to 1, i.e. 90% of schooled individuals did not develop dementia compared to their unschooled agematched counterparts. Occupational attainment showed a similar protective effect, although whether this is due to higher education can not be ruled out. These data emphasize from a social level, the impact that non-genetic risk factors have from a young age on the future burden of dementia.Younger individuals (<65 years) with symptoms matching the DSM-IV criteria have a higher likelihood to have a strong genetic component. In early-onset AD, autosomal dominant inheritance (3 generations affected, e.g. PSEN1) is possible, whereas in lateonset AD, APOE genetic testing may be useful; however, AD is genetically heterogeneous. The APOE ε4 may indicate that the dementia is of vascular origin as it only advances the onset, it doesn't change the risk. For patients aged >65 years, genetic explanations are much less likely. Moreover, genetic analysis should not be considered deterministic; it simply offers the patient, family and doctor a chance to be more careful and proactive about prevention.The risk factors of coronary artery disease, smoking, hyperhomocysteinemia, diabetes mellitus, hypertension, high dietary saturated fat and cholesterol...