Dementia is a broad category of degenerative diseases characterized by a progressive decline in cognitive function in more than one of the following areas:
- (Recent memory).
- (Aphasia) Speech change.
- Apraxia) Inability to perform motor tasks despite normal muscle strength.
- (Agnosia) Inability to comprehend sensory information, i.e., vision.
- (Executive function) Planning, organization, sequencing, abstracting.
Loss of recent memory is the initial symptom in Alzheimer’s disease but memory loss alone is not adequate to make the diagnosis which requires difficulty in at least one of the other domains.
Alzheimer’s disease is the most common form of dementia. In 1901 Alois Alzheimer described a case of Auguste D – a 51-year-old with disorientation, delusions, aphasia and behavioral problems. Post-mortem evaluation (published in 1911) described classical findings of neurofibrillary tangles and neuritic plaques. This disease typically has an insidious onset of the disease duration between 2 and 20 years.
Another form of dementia are Parkinsonian dementias. Parkinson’s disease itself begins with motor problems such as tremor and rigidity and has later onset dementia. Lewy body dementia (the second most common form of dementing illness) accounts for approximately 20% of all dementias. This was first described in 1996. There are other Parkinsonian dementias as well, those are less common.
Frontal temporal degeneration is the third most common form of dementia accounting for between 3% and 16% of all dementing illnesses. This can present as isolated speech change or bizarre behaviors/personality changes. It can even be accompanied by motor neuron disease (i.e., Lou Gehrig’s disease). This form of dementia has a younger age of onset and survival is only between 2 and 8 years.
There are another group of dementias known as rapidly progressive dementias which have a much shorter course (months to one year). This would include things like various forms of brain infection, metabolic problems, autoimmune disorders, brain cancer, or Creutzfeldt-Jakob disease (i.e., mad cow disease).
Many of the above disease processes have significant overlap with one another. For example, it is very common for Parkinson’s patients or patients with Lewy body dementia to have Alzheimer’s pathology. There is a great deal of research taking place on all of these dementias but most of the focus on research for treatment is on Alzheimer’s because it is by far the most common of the above conditions.