Alzheimers dementia, by far, is the most common cause of dementia in the US. The second most common is vascular dementia, usually caused by a lifetime of hypertension and atherosclerosis, with minor occlusions that eventually build up to something much more noticeable. The third most common cause of dementia is Lewy Body Dementia.
Lewy Bodies are cytoplasmic inclusions in substantia nigra cells. These inclusions can be found in Parkinsons disease as well. In Lewy Body Dementia, patients can also exhibit signs of Parkinsons disease, just as Parkinsons disease patients can have dementia. The major difference between the two is which comes first, the dementia or the movement disorder. In Lewy Body Dementia, the dementia comes first. In Parkinsons disease, the movement disorder comes first.
Lewy Body Dementia is marked by not only dementia, but also altered states of consciousness (staring into space, falling asleep for long periods of time during the day even with a full good nights sleep the previous night) and psychotic features such as hallucinations and delusions. These features set Lewy Body apart from Alzheimers.
Treatment is mostly symptom control and attempting to slow progression with cholinsterase inhibitors. If hallucinations are violent, the patient may require a neuroleptic, but receiving such medications has been shown to increase mortality.