Frequency of Dementia Varies By Age, Diagnosis, Placement

JULY 15, 1996 VOLUME 4, NUMBER 3

The common usage of “dementia” usually refers to loss of intellectual functioning or diminished mental capacity. Frequently, the term is used to describe any of a wide variety of illnesses or conditions, without distinguishing among the possible causes.

In a similar way, “Alzheimer’s” is commonly used to describe almost all demented individuals, regardless of the actual reason for the diminution of capacity. It is commonly understood that Alzheimer’s Disease is a diagnosis of exclusion; other than autopsy, it is usually impossible to definitively diagnosis Alzheimer’s, and the diagnosis is reached by excluding all other possible diseases.

For many purposes, the difference between a diagnosis of Alzheimer’s and, for example, vascular dementia is unimportant. Most dementias are irreversible, and there is little evidence to suggest that the progress of many dementing illnesses can be slowed. Still, it is both important and interesting to know what different illnesses might cause dementia, and the relative frequency of each.

In their 1992 book “Dementia: A Clinical Approach,” medical researchers Jeffrey L. Cummings and D. Frank Benson survey the existing literature about dementia. Among demented patients, the frequency of each cause varies according to the researcher. Cummings and Benson caution that the estimates of Alzheimer’s disease, in particular, are almost certainly overstated, but the research suggests the following frequencies:

  • Alzheimer’s Disease–25-50%
  • Vascular (multi-infarct) Dementia–10-25%
  • Depression and other psychiatric disorders–10-20%
  • Alcoholic Dementia–2-12%

Other causes, each accounting for between one or two percent and ten percent of all dementias, include metabolic conditions, infections, toxic conditions, Huntington’s and Parkinson’s diseases and other, less frequent causes.

Clearly, Alzheimer’s Disease is the most common dementing condition, but other causes collectively account for more dementia. The very fact that Alzheimer’s is a diagnosis of exclusion operates to inflate its reported frequency, since unidentified dementias will usually be lumped into that category.

Cummings and Benson also report several studies about the frequency of dementia in various groups. Among those 65 or over, approximately 6% can be expected to suffer from severe dementia, and another 10% to 15% evidence mild to moderate impairment.

The frequency of dementia, not surprisingly, increases with age. The percentage of demented individuals can be expected to double for each five-year increment in age, so that about 20% of those over age 75 will show severe symptoms of dementia.

Dementia should be expected to appear more frequently in more restrictive medical facilities, and that expectation is borne out by the research. About 54% of state hospital patients demonstrate severe dementia, while 30% of nursing home residents and 15% of retirement community residents are severely demented. Mild dementia (or worse) can be expected in 94% of state hospital patients, 87% of nursing home residents and 80% of retirement community residents.

What do these figures mean for the treatment or care of demented patients? The high frequency of dementia other than Alzheimer’s Disease suggests the importance of differential diagnosis of dementing illnesses. While most dementia is irreversible, some (such as metabolic conditions and infection) may be treated, and the progress of others (notably vascular dementia) may be slowed by drug therapy and/or diet. And diagnosis and treatment regimens become more important with age and type of treatment facility.

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