Common Types of Dementia

This is the most common cause of dementia, accounting for about two thirds of cases in those aged 65 and above. In truth, we don't really know what causes it but the presence of abnormal forms of two proteins - amyloid and tau - is necessary to make a conclusive diagnosis. Traditionally, these proteins could only be detected post-mortem - by looking at samples of brain tissue. Excitingly though we have now developed brain scans that give a good indication about how much amyloid and tau is in the brain when a person is living. In Australia, these scans are only available to researchers but that will hopefully change with time.

Typical Alzheimer's disease starts with difficulty remembering new things - generally presenting as forgetfulness of recent events and conversations. Memory of things from long ago tends to be more robust and is often not lost until later in the journey. Disorientation can occur early on, especially with regard to knowing days and dates. As the disease spreads, there may be problems with planning and organisation as well as language and calculation. Recognition of familiar objects may falter and familiar people may be forgotten. These are so called cognitive symptoms, but there are often also changes in behaviour and psychological changes such as anxiety, depression and agitation. In the later stages, physical abilities become impacted, leading potentially to problems walking, speaking and swallowing as well as incontinence. It is important to realise, however, that many of these things can be well treated and managed with the right supports.

This type of dementia is caused by impairment of blood supply to the brain, either because of blood clots lodging in large or small blood vessels or through the vessel walls breaking and blood leaking into the surrounding brain tissue. The symptoms can be quite varied and depend to on which part of the brain is affected. Memory impairment is common, though often it is the recall of the memory that is faulty, meaning that with sufficient time and clues, the information will come out. This contrasts to Alzheimer's disease where new memories often don't go in in the first place and providing clues is of little help. Changes in mood seem to occur commonly with vascular disease - especially depression - and there may be a general slowing of thinking. Disorganisation can occur, along with concentration difficulties and problems with planning.

Vascular dementia and Alzheimer's dementia often occur together - especially where the dementia occurs in late life - and each one seems to increase the risk of the other.

Lewy bodies are an abnormal deposit of another protein - alpha-synuclein - and if there are sufficient of them in the brain, they can cause dementia. Lewy bodies also exist in Parkinson's disease, condition that can also result in dementia. Lewy body dementia often has quite striking and characteristic symptoms and signs - someone with the condition may rapidly fluctuate in their level of consciousness and confusion, going from being reasonably lucid and alert one moment to confused and lethargic the next. There are often pronounced changes in visuospatial skills and there may be visual hallucinations which can be quite vivid and distressing. With time, the physical features of Parkinson's disease usually appear - hand tremors, increased muscle tone and stiffness and slowed movements.

Lewy body dementia and Alzheimer's disease also seem to occur together at times.

This type of dementia affects the frontal lobes or the temporal lobes of the brain and can itself be due to a number of damage-inducing proteins. It is one of the most common causes of younger-onset dementia (defined as starting before the age of 65).

If it mostly affects the front part of the brain, the changes are are often, initially at least, mainly behavioural and psychological. They might include apathy, irritability, impulsivity, mood changes, anxiety or compulsive behaviours. Some people with this so calledfrontal variant or behavioural variant may start to act inappropriately, perhaps with a loss of their normal social inhibitions.

If the temporal lobe is most affected, the problem is mainly with language - either in the ability to express yourself (in speech and writing) and/or the ability to understand what is being said to you.

Unlike Alzheimer's disease, memory can be reasonably well preserved early in the disease process.