Prevalence of
dementia varies among epidemiological studies, depending on the ages of the
subjects sampled, method of determining the presence, severity and type of
cognitive impairment and the regions or countries studies community studies
estimated a one year prospective prevalence of almost 3.0% with severe
cognitive impairment in the adult population. The study assessed individuals
with a brief instrument that assessed current cognitive status. Which does
not identify specific diagnosis. It is estimated that 2-4% of population
over 65 years have dementia of Alzheimer’ Type, with other types being much
less common. The prevalence of dementia especially dementia of the
Alzheimer’s type and vascular dementia, increases with age. Particularly
after age 75 years with a prevalence of 20% or more over age 85 years.
EPIDEMIOLOGY
Dementia is essentially a
disease of older people. In the united states, approximately 5 percent of
people older than age 65 have severe dementia and 15 percent have mild
dementia of those older than age 80, approximately 20 percent have severe
dementia of all patients with dementia 50 & 60 percent have the most common
type of dementia, dementia of the Alzheimer’s type. About 5 percent of every
one who reaches age 65 has dementia of the Alzheimer’s type, compared with
15% to 25% of everyone age 85 or older patients with dementia of Alzheimer’s
type occupy more than 50 percent of nursing home beds. Over 2 million person
with dementia are cared for in these homes. The risk factors for the
development of dementia of the Alzheimer’s type include being female, having
a first degree relative with the disorder, and having a history of head
injury. Down’s syndrome is also characteristically associated with the
development of dementia of the Alzheimer'’ type.
Alzheimer’s type
generally occurs in late life, most commonly in the 60s, 70s and 80s and
beyond , but in rare instances the disorder appears in the 40s and 50s
(known as early-onset dementia) . The incidence of Alzheimer's disease also
increase with age and it is estimated at:-
0.5 % Per year from age
65 to 69
1 % Per year from age 70
to 74
2 % per year from age 75
to 79
3 % Per year from age 80
to 84
8 % Per year from age 85 onwards.
Progression is gradual
but steadily down ward, with an average duration from onset of symptoms to
death of 8 to 10 years. Plateaus may occur, but progression generally resume
after 1 to several years.
The second most common
type of dementia is vascular dementia, which is causally related to
cerebrovascular diseases. Hypertension predisposes a person to the disease.
Vascular dementia accounts for 15 to 30% of all dementia cases. Vascular
dementia is most common in people between the ages of 60 and 70 and is more
common in men than in women. Approximately 10 to 15% percent of patients
have coexisting vascular dementia of the Alzheimer’s type.
Other common causes of
dementia, each representing 1 to 5 percent of all cases, include head
trauma, alcohol related dementias, and various movement disorder related
dementia’s such as Huntington’s disease and Parkinson’s disease. Because
dementia is a fairly general syndrome. It has many causes and clinicians
must embark on a careful clinical workup of a patient with dementia to
establish its cause.
The current annual cost
of caring for patients with dementia is 15 billion, which is likely to
increase. By the year 2030, an estimated 20% of the population will be older
than age 65.
