Dementia is a clinical diagnosis, supported by objective brain-function testing and imaging. It can be a tricky thing to diagnose, perhaps even requiring multiple visits to a GP so that they can establish a trend. As we get older, our brain function will gradually decline. If this decrease makes remembering things a little bit trickier, but we can still go about our business independently - this is labelled as mild cognitive impairment. However, if our brain function decreases to a point that we struggle to do our daily tasks independently - this is called dementia. 

If you think a loved one may have cognitive impairment or dementia, you will likely bring them to the GP. Here, they will take a detailed history - trying to ascertain the level of struggle in daily living attributable to a declining brain (memory, language, etc.).
They will perform an objective mental test, such as the 'MOCA', to give the doctor a score, off which to compare future performance and to aid a current diagnosis. 
They will order brain imaging (CT, MRI or PET) - to look for visual abnormalities that may support the decline in brain processing ability, and rule out any other cause (such as a tumour).
They will also send off an array of blood tests, including vitamin B12 and thyroid hormone levels. Sometimes, a decline in brain function is attributable to a correctable underlying cause. After all of this, the GP may be able to make a diagnosis and conclude what type of dementia it is. 

We will discuss four common types of dementia - Alzheimer's, Vascular, Frontotemporal, and Lewy Body. Very often, patients will have a mix of these affecting cognitive function.

Alzheimer's disease is the famous one, a form of dementia renowned for its affect on memory. This is often coupled with mood and personality changes. When the brain is put under the microscope, amyloid plaques, tau proteins and neurofibrillary tangles are seen, the result of neuron loss and degeneration. These calling cards are seen mostly in the hippocampus - a region of the brain that transfers short-term memory to long-term memory. 

Vascular dementia is a form of cognitive decline caused by worsening blood supply to the brain leading to brain cell damage (usually from many, minor strokes). Risk factors for developing vascular dementia are the same as the risks for developing strokes (obesity, diabetes, smoking, high blood pressure, etc.). Patients usually start having trouble with making basic decisions and exemplify poor planning of daily tasks. 

Frontotemporal dementia majoritively affects the frontal and temporal lobes. The frontal lobe is known to house our personalities. This form of dementia can result in complete personality changes and is characterised by a lack of inhibition, including inappropriate sexual behaviour. Patients often develop problems with understanding language and speaking - this is caused by the involvement of the temporal lobe. 

Lewy body dementia is named so due to the "lewy body" protein deposits seen on brain imaging. It is often confused clinically with dementia caused by Parkinson's disease. Both diseases affect movement, thinking ability and mood. Lewy body dementia has a few hallmark symptoms, such as visual hallucinations or lucid dreaming. 

Dementia is an irreversible disease process, however - the rate of decline can be slowed in some instances with medication. The medications work by tampering with the level of certain chemicals the brain use for messaging, communication between neurons. 
One group are the acetylcholinesterase inhibitors (the drug name usually ends in "stigmine"). 
Another group are the NMDA receptor antagonists, involved in blocking the chemical glutamate (an example of such is "Memantine").

Other treatments are tailored to reduce the symptoms of dementia - such as anti-depressants or anti-psychotics.