WHAT ARE THEY AND HOW DO THEY DIFFER ?

Dementia is a condition that is acquired, meaning that it develops over time. It is more common in older age. This is not because dementia is caused by aging, but rather the diseases that cause dementia occur more often as you age (e.g., Alzheimer's disease, Parkinson's disease).

The two most common causes of dementia include Alzheimer s disease and vascular dementia (dementia due to strokes). But there are more than 55 different diseases that can cause dementia, and you should consult your doctor to be sure.

How Will My Doctor Know If I Have Dementia?

Unfortunately, there is no specific blood test or x-ray that can confirm you have dementia. Your doctor can only try to determine if you have dementia by looking at your general health (e.g., if you have Alzheimer's disease) and how that disease is affecting you. There is a test, however, that they can give to determine brain misfunction; it is a basically a mental exam.

Treatment depends on what is causing your dementia. For example, if your dementia is due to a stroke, your treatment will try to prevent you from having another stroke. Not everyone can get rid of their dementia, but most forms of dementia can be treated effectively.

Alzheimer’s disease [AD] is characterized clinically by early memory impairment followed by language and perceptual problems. A key feature in the development of the disease is believed to be an abnormal protein b -amyloid which is deposed in the centre of the senile plaques. These can be seen together with neurofibrillary tangles under the microscope.

AD may be sporadic or familial and the age of onset may vary enormously from around forty to over ninety, although it is predominantly a disease of old age. In familial cases, the age at onset within a family may be fairly constant.

Several abnormalities in the genetic make up (gene mutations) have been identified in individuals with familial AD; the cause agent of the sporadic form of the illness is probably multifactorial.

The gene responsible for making the amyloid protein is on chromosome 21 and a mutation in this gene has been shown to cause AD in three families in Britain and about fifteen families world-wide. Many of the families that have a very young age of disease onset have been shown to have a mutation in a gene on chromosome 14 now called Presenilin 1. So far at least 25 different mutations have been described. Mutations in a similar gene, Presenilin 2, on Chromosome 1 have also been described; the age at onset in these families is later. In these families the inheritance is autosomal dominant.

Late onset AD has been linked with chromosome 19 and type of Apolipoprotein. Although there is an increased predisposition to AD with the genotype Apolipoprotein 4 it is not conclusive and it is possible to have AD but not Type 4 and likewise to have Type 4 but not develop AD.

Neuropathologically, the different forms of AD cannot yet be differentiated.

FRONTAL LOBE DEGENERATION

A frontal dementia but without the typical changes seen on neuropathological examination in Pick’s disease (more on Pick's disease at the end of this page) although cell loss in the frontal lobes is apparent. The onset is usually slow with only changes in personality seen for some time. This is followed by changes in mood and behavioural disturbance. It may be sporadic or familial, and an as yet unidentified mutation on a gene on Chromosome 17 is believed to be the cause of some cases.

FRONTOTEMPORAL DEMENTIA

This is a clinical term to describe patients with personality (frontal lobe) or language (temporal lobe) changes. It includes the specific diseases of Pick’s disease and frontal lobe degeneration amongst others.

LEWY BODY DEMENTIA

Lewy Body dementia has been increasingly recognised over the past 5-10 years. Lewy bodies are areas of abnormal staining (distinct from Pick bodies and neurofibrillary tangles) found within brain cells. They are found in a particular area of the brain stem, the substantia nigra, in Parkinson’s disease. In Lewy body dementia they are found in the cerebral cortex, either alone or in combination with the senile plaques of Alzheimer’s disease. Lewy body dementia may present as:

1. late onset Parkinson’s disease followed months or years later by visual hallucinations, episodes of confusion, memory loss and then global dementia, or
2. cognitive or psychiatric symptoms followed by milder Parkinsonian features later in the course of the disease.

The main pointers to a diagnosis of Lewy Body disease include:

• fluctuating cognitive performance with episodes of confusion
• hallucinations and/or paranoid delusions
• early gait disturbance
• any combination of rigidity, bradykinesia, tremor and flexed posture
• temporoparietal dementia with inattention in a patient with Parkinson’s disease

People with Lewy Body dementia may also have problems with their short term memory, word finding difficulties, difficulty sustaining a line of thought and problems locating objects in space. They may also experience symptoms of anxiety and depression.

Anybody can develop Lewy Body disease. Studies which have looked at the brains of people with dementia after they have died suggest that it is relatively common although prevalence figures do vary. It appears to affect men and women alike.

As yet it is impossible to identify risk factors for developing the disease. However, rare ‘familial’ cases of Lewy Body disease have been described. Although there is no cure for Lewy Body disease it is sometimes possible to treat some of the symptoms of this disease. The depression which accompanies this disease for example will usually respond to antidepressant therapy.

PICK’S DISEASE

In 1892, Arnold Pick, a German neurologist, described a man who had presented in life with progressive loss of language. After death the patient’s brain was shown to have asymmetric atrophy as opposed to Alzheimer’s disease where the atrophy is more general. In Pick’s disease the frontal and temporal lobes are most affected. In addition, brain cells in these areas are sometimes found to be abnormal and swollen. These abnormal cells (Pick cells) together with the presence of abnormal staining within cells (Pick bodies) are the hallmark of the disease.

When these typical features are not seen on post mortem examination but the same areas of the brain are affected by cell death, the case may be described as Pick’s syndrome or frontotemporal Dementia.

Pick’s disease varies in the way it affects individuals. There are however, a common core of symptoms. Some or all of these may be present at different stages of the disease.

The more common symptoms include:

• personality change: loss of inhibitions/rudeness/impatience/inappropriate behaviour
• failure to recognise objects
• using objects wrongly
• development of routines
• speech problems, echolalia (repeating what is said to the patient)
• overeating, changes in dietary preference, obsessional cravings for certain types of food
• attention problems
• changes in sexual behaviour

Anybody can develop Pick’s disease. It affects men and women alike. Although it typically affects people in their 50s and 60s it has been diagnosed in people from the ages of 20 to 80. It does exist as a familial disease [autosomal dominant] in some families, but the majority of cases are sporadic. The rate of progression varies enormously ranging from a duration of less than 2 years to well over 10 years.

*Information gathered from many sources on the web