Michaud: Diagnosing Alzheimer’s

Alzheimer’s disease is prevalent in today’s society, with an incidence rising from 1% at ages 70 – 74 to more than 8% in individuals age 85 and older. As the population ages, the burden of Alzheimer’s disease will continue to increase.

The cause of the disease is unclear. Approximately 10% of cases show early onset and autosomal dominant inheritance. These families usually have family histories of early onset Alzheimer’s disease in multiple generations. Genetics also appears to play a role even in the more common, later onset Alzheimer’s disease.

Alzheimer’s disease is the most common of the many diseases that cause the syndrome of dementia. To diagnose Alzheimer’s disease, one first has to make a diagnosis of dementia, and then run through the list of causes of dementia, employing various criteria to come up with the likely cause.

Alzheimer dementia is characterized by a gradual onset and continuing decline in cognitive function, leading to impairment in social or occupational function. Recent memory is impaired and there will also be impairment in at least one of the following: language, skilled motor activity, abstract reasoning, or visual processing.

In contrast, vascular or multi-infarct dementia may come on more suddenly, sometimes after a stroke and may show a jerky or stepwise decline due to successive small strokes rather than the smooth continuous decline of Alzheimer’s disease.

Cerebral imaging will show multiple brain infarcts in vascular dementia, but this is usually normal in Alzheimer’s disease. Dementia itself may not be obvious to the casual observer. The patient frequently does not complain of memory loss. Most often it is the family who will bring the symptoms of dementia to the attention of a physician.

Frequently, this does not occur until the symptoms have become so advanced that the family can no longer ignore them or attribute them to other causes.

The Mini-Mental State Exam (MMSE) is a brief office test that is commonly used to detect dementia. A score of 24 or less (out of 30) is considered evidence of dementia, but this has to be interpreted within the context of the individual’s previous language skills and education level. A score of 26 or 27 may indicate dementia in a previously articulate welleducated individual, but would be considered normal for someone with 8 years of schooling or less.

What is the life expectancy of someone with Alzheimer ’s disease ? The answer turns out to be surprisingly difficult to determine. This is because the onset of the disease is insidious and often the diagnosis does not occur until years after the first symptoms have occurred. Various studies have estimated the life expectancy from “onset” of dementia at anywhere from 3 to 9 years. It is clear that individuals with dementia have lower life expectancy than their non-demented age-matched peers, especially at younger ages. Not surprisingly, the severity of dementia (lower MMSE score) is a predictor of shorter life expectancy. A history of falls or gait disturbance and the presence of co-existing disease such as heart failure or diabetes also are predictive of lower life expectancy.