What is Dementia?

Dementia refers to a state of generalized and persistent decline in cognitive and intellectual functions that interferes with a persons’ ability to deal effectively with everyday activities.  Dementia is not due to aging but rather, refers to a pathological brain syndrome that affects a variety of human behaviors.  There are many causes of dementia and hundreds of dementing conditions. 

In dementia there is usually impairment in recent memory functioning and in some cases, long term memory will be affected.  Abstract reasoning, judgment and emotional functions are also affected.   Some patients will develop signs of cortical impairment such as aphasia, apraxia and agnosia.   Aphasia refers to problems with language functions and can include word finding problems and problems expressing ideas or understanding language.  Sometimes writing, calculation and reading skills are affected.  Apraxia refers to problems with skilled motor movements and actions and can involve the hands as well as the mouth and other body parts.  Agnosia refers to perceptual problems  that can be quite complex and diverse.  One example is anosagnosia, which is a lack of awareness of one’s own cognitive, motor or sensory problems.  Some patients will also have constructional impairment which refers to impaired drawing ability and related problems with spatial analysis or visual-motor functions.

Rates of Dementia

Approximately .5% to 16% of dementia cases world-wide are mildly impaired.  From 2% to 8% are moderately to severely impaired. Prevalence is strongly age dependent and rates double for each five  year interval between 60 and 95 years.  Roughly 1% of people below age 65 have moderate to severe dementia   compared to approximately 40% of 90 to 95 year olds.   In the United States, about 1.5 million citizens have disabling dementia.  It is estimated that an additional 1 to 5 million Americans have mild to moderate dementia.  As our population ages there will be greater numbers affected.  By 2050, there will be more than 7 million Americans with disabling dementia.

Dementia of the Alzheimer Type

Alzheimer’s Disease is the most common form of dementia.  Approximately 69% of cases are classified as probable dementia of the Alzheimer type.  Senile Dementia of the Alzheimer’s Type (SDAT) has an insidious onset with a generally progressive deteriorating course.  By definition, other causes of dementia must be ruled out or considered of secondary importance.  A definitive diagnosis of SDAT requires confirmation by autopsy of the presence of neuritic plaques which contain beta-amyloid protein and neurofibrillary tangles.  Brains of AD patients show signs of atrophy far greater than expected for age.  Additionally,  40% to 60% of cortical neurons are destroyed, especially in the hippocampus and related structures causing a disconnection between basic memory centers and the rest of the brain.  Striking changes in the cholinergic neurotransmitter systems are also seen.  

Clinical diagnosis of probable SDAT requires the presence of dementia; deficits in two or more areas of cognition; progressive worsening of memory and other cognitive changes; no disturbance of consciousness; onset between ages 40 and 90 years; and a relative absence of other causes of dementia.  

Close relatives of patients with SDAT can be at greater risk of developing the disorder compared to general population risk, but the magnitude of increased risk is not known.  In about 60% of families, only a single individual is afflicted with AD.  

Neuropsychological testing is required for a diagnosis of probable SDAT.  Tests of memory, language, and psychomotor integration are particularly sensitive to mild SDAT and are generally more useful in detecting early phases of the illness than CT or clinical EEG.