Alzheimer’s disease: the most common cause of dementia. An illness which alters the chemistry and structure of the brain, causing brain cells to die. Alzheimer’s disease usually begins with mild symptoms, typically memory loss, and progresses gradually. People with Alzheimer’s disease often live for ten or more years after symptoms first become apparent. Alzheimer’s disease was first identified by the German neurologist Alois Alzheimer in 1906.
Early onset dementia: dementia which develops before the age of 65. (It is preferable to use the term young onset dementia for this condition, to avoid confusion with the situation where someone has recently developed symptoms of dementia (at any age) and might be said to be at an early stage of dementia.)
Frontotemporal dementia: a rare form of dementia, caused by damage to the frontal lobe and/or temporal parts of the brain. At an early stage, memory usually remains intact while personality and behaviour – including social skills and the ability to empathise with others – may change radically. Language skills may also become damaged. At a later stage, symptoms are usually similar to those of Alzheimer’s disease. Frontotemporal dementia may develop at any age, but is more likely to affect people under 65.
Lewy body dementia: (also known as dementia with Lewy bodies) is a type of dementia in which abnormal protein deposits, known as Lewy bodies, develop inside nerve cells in the brain, interrupting the brain’s normal functioning. A person with this type of dementia typically fluctuates in their mental abilities from day to day, and may experience hallucinations. Some symptoms are similar to those of Parkinson’s disease, including tremors and slowness of movement.
Mixed dementia: is the name given to the condition where a person has symptoms of both Alzheimer’s disease and vascular dementia.
Parkinson’s dementia: People with Parkinson’s disease have a higher than average risk of developing dementia. Parkinson's disease is a progressive disease of the nervous system which affects the ability to coordinate movement. It is characterised by a pronounced tremor, slowness of movement and stiff muscles which may lead to an expressionless face. The illness was first identified by the London doctor James Parkinson in 1817.There is more information about Parkinson's dementia here.
Pick’s disease: a type of frontotemporal dementia (see above)
Vascular dementia: is dementia caused by interruptions in the blood supply to the brain, usually following a stroke or a series of small strokes. Many of the symptoms of vascular dementia are similar to those of Alzheimer’s disease, but whereas the progression of Alzheimer’s disease tends to be gradual, and is usually pictured as a downward slope, in vascular dementia it is usually pictured as a descending staircase, where sudden noticeable deterioration occurs at intervals. At present the drugs typically prescribed for people with Alzheimer’s disease are not thought to benefit people with vascular dementia and are not usually prescribed. People with vascular dementia are more likely to be prescribed treatment which may help to reduce the effect of underlying conditions such as high blood pressure.
Young onset dementia: (sometimes known as early onset dementia, but the term young onset dementia is preferable) dementia which develops before the age of 65.
The Alzheimer's Society provides lots of information about different types of dementia on their website.