Other coincident diseases such as heart problems, diabetes, or history of alcohol abuse are also related with shortened survival. While the earlier the age at onset the higher the total survival years, life expectancy is particularly reduced when compared to the healthy population among those who are younger. Men have a less favourable survival prognosis than women.Pneumonia and dehydration are the most frequent immediate causes of death brought by Alzheimers disease, while cancer is a less frequent cause of death than in the general population. Epidemiology
Two main measures are used in epidemiological studies: incidence and prevalence. Incidence is the number of new cases per unit of person-time at risk (usually number of new cases per thousand person-years); while prevalence is the total number of cases of the disease in the population at any given time. Regarding incidence, cohort longitudinal studies (studies where a disease-free population is followed over the years) provide rates between 10 and 15 per thousand person-years for all dementias and 5–8 for Alzheimers disease, which means that half of new dementia cases each year are Alzheimers disease. Advancing age is a primary risk factor for the disease and incidence rates are not equal for all ages: every 5 years after the age of 65, the risk of acquiring the disease approximately doubles, increasing from 3 to as much as 69 per thousand person years. Females with Alzheimers disease are more common than males, but this difference is likely due to womens longer life spans.
For mild neurocognitive disorder due to Alzheimers, probable Alzheimers disease can be diagnosed if there is genetic evidence, whereas possible Alzheimers disease can be met if all of the following are present: no genetic evidence, decline in both learning and memory, two or more cognitive deficits, and a functional disability not from another disorder.The NIA-AA criteria are used mainly in research rather than in clinical assessments. They define Alzheimers disease through three major stages: preclinical, mild cognitive impairment (MCI), and Alzheimers dementia. Diagnosis in the preclinical stage is complex and focuses on asymptomatic individuals; the latter two stages describe individuals experiencing symptoms. The core clinical criteria for MCI is used along with identification of biomarkers, predominantly those for neuronal injury (mainly tau-related) and amyloid beta deposition. The core clinical criteria itself rests on the presence of cognitive impairment without the presence of comorbidities. The third stage is divided into probable and possible Alzheimers disease dementia. In probable Alzheimers disease dementia there is steady impairment of cognition over time and a memory-related or non-memory-related cognitive dysfunction. In possible Alzheimers disease dementia, another causal disease such as cerebrovascular disease is present. Techniques
Neuropsychological tests including cognitive tests such as the Mini–Mental State Examination (MMSE), the Montreal Cognitive Assessment (MoCA) and the Mini-Cog are widely used to aid in diagnosis of the cognitive impairments in AD.