Dementia is a cognitive disorder in which there is usually a gradual impairment of brain functioning. This results in difficulties in remembering, reasoning, judgment, and language skills severe enough to interfere with daily functioning. Dementia may have many causes, some of which are treatable and some, not treatable. Some are reversible and some, irreversible. An example of the irreversible type is Alzheimer’s disease, which is responsible for approximately half of dementia cases and is the major subtype of the dementia classification. The other three subtypes of dementia are vascular dementia, substance-induced dementia and dementia caused by other general medical conditions.