Types of dementia
Although there are more than one hundred diseases that come under the umbrella term of ‘dementia’, some are more common than others. The most common ones are listed below, but remember that each individual will experience dementia differently – talk to your doctor for a proper diagnosis.
Alzheimer's diseaseis the most common cause of dementia (50-70%). As Alzheimer’s progresses, physical changes occur in the structure of the brain – brain cells die and the brain shrinks, especially in the inner parts of the temporal lobes. Plaques and tangles form in brain tissue and disrupt messages between brain cells, preventing the brain from working efficiently. People with Alzheimer's disease experience a gradual decline in their ability to remember, understand, communicate and reason. Some medications are available, which may mask the progression of Alzheimer's disease in the early stages.
Also called multi-infarct dementia, vascular demtentia is the second most common form of dementia (20-30%), affecting slightly more men than women. It is most commonly caused by multiple strokes and, occasionally, by a single stroke. A stroke occurs when blood flow in the brain is blocked by a blood clot in an artery or when an artery bursts. When this happens, brain cells are deprived of oxygen and die. People who have a large stroke will usually experience difficulties such as paralysis on one side of the body, speech and language problems, or difficulties with coordination and movement. Some small strokes may just cause a 'funny turn' or not be noticed at all. However, each stroke is contributing to a build-up of damage to the brain, which can cause dementia.
Anyone can be affected by vascular dementia, but several factors increase the risk. These include:
- High blood pressure
- High cholesterol
- History of mild warning strokes
- Evidence of disease in arteries elsewhere
- Heart rhythm abnormalities
Vascular dementia is usually diagnosed through neurological examination and brain scanning techniques such as computerised tomography (CT) or a magnetic resonance imaging (MRI) test. Vascular dementia can be very difficult to distinguish from other forms of dementia and it is common to have both Alzheimer's disease and Vascular dementia.
Symptoms of vascular dementia are very similar to Alzheimer's disease. However, distinguishing features include neurological symptoms including weakness, clumsiness, or altered sensation in the limbs or face.
Some of the abilities lost in people with Alzheimer's disease may remain relatively unaffected in people with vascular dementia, since the condition affects the brain in a patchy fashion - symptoms can remain steady for a while and then suddenly decline. People with vascular dementia may also understand what is happening to them, more so than those with other forms of dementia, and this can make them prone to depression.
Dementia with Lewy Bodies
Dementia with Lewy Bodies (DLB) affects men more than women and is more prevalent in people over the age of 65. DLB is similar to Alzheimer's disease in that it is caused by the degeneration and death of nerve cells in the brain. Lewy bodies are tiny protein deposits found in nerve cells and their presence disrupts the brain's normal functioning, interrupting the action of important chemical messengers. Lewy bodies are also found in the brains of people with Parkinson's disease and researchers do not yet fully understand why Lewy bodies occur in the brain.
Symptoms of DLB include:
- Muscle stiffness and trembling
- A fluctuating ability to complete tasks from hour to hour, or even from minute to minute
- Fainting or falling
- Unexplained turns
- Visual hallucinations
- Memory loss and disorientation
- Communication difficulties
- Slowness and/or tendency to shuffle when walking
- Loss of facial expression
- Changes in strength and tone of voice
DLB and Parkinson’s disease share many of the same symptoms. An accurate diagnosis is important, as people with DLB can react badly to neuroleptic drugs – strong tranquillisers which are often prescribed to people with dementia. There is currently no cure for DLB and while some people may benefit from anti-Parkinson's disease drugs, they may worsen hallucinations and confusion.
Fronto-temporal lobe dementia
Fronto-temporal lobe dementia (FTLD) is caused by a degeneration in one or both of the frontal or temporal lobes of the brain.
The right and left frontal lobes govern mood, behaviour, judgement and self-control. Damage leads to alterations in personality and behaviour, changes in the way a person feels and expresses emotion and loss of judgement.
The right and left temporal lobes are involved in the organisation of sensory input, such as sight and sound. Damage may lead to difficulty placing words or pictures into categories.
FTLD is a relatively rare type of dementia usually affecting people under the age of 65, and symptoms may vary depending on which parts of the frontal and temporal lobes are affected. Common symptoms of FTLD may include:
- Loss of insight and the ability to empathise with others, appearing selfish and unfeeling
- Extroversion when previously introverted, or withdrawing when previously outgoing
- Inappropriate behavior, including tactless comments, ill-timed jokes, or rude actions
- Loss of inhibitions, such as exhibiting sexual behaviour in public
- Compulsive routines and rituals
- Overeating and/or developing a liking for sweet food
- Reduction in or lack of speech, including difficulty finding the right words and/or inability to have spontaneous conversation
In the later stage of the disease, those affected may no longer recognise friends and family and may need nursing care.
Fronto-temporal dementia is commonly misdiagnosed as Alzheimer's disease, but a specialist may be able to diagnose FTLD by questioning the person affected and by taking a detailed history of their symptoms. Brain imaging scans may be also used to determine the extent of damage to the brain.
Other types of dementia and related conditions
Other types of dementia include (but are not limited to):
Alcohol-related dementia (Korsakoff's syndrome)
Infection related dementia (AIDS-related cognitive impairment)