The term dementia comes from the Latin words de (away from, apart) and mens (mind). It is used to denote a generalized, pervasive decline in cognitive functioning to an extent which is beyond what can be expected in normal ageing, and which leads to a significant interference with the affected individual's daily functioning, social functioning, and/or occupational activities. Eti-ologically, dementia is associated primarily with a variety of CNS diseases, including Alzheimer's disease, cerebrovascular disease (leading to vascular dementia), Pick's disease, Parkinson's disease (i.e. Lewy body dementia), Huntington's disease, " Aids (leading to the Aids-dementia complex), Creutzfeldt-Jakob disease, alcoholism (leading to alcoholic dementia), and substance abuse. Among the hallucinations occurring in the context of dementia, the " visual and " auditory ones are the most prevalent. However, hallucinations in dementia may occur in any of the other sensory modalities as well. Hallucinations and illusions in dementia usually arise after the characteristic process of cognitive impairment has set in, but occasionally they constitute the disease's presenting symptom. For more specific details, see the entry Alzheimer's disease and hallucinations.
References
Haddad, P.M., Benbow, S.M. (1992). Visual hallucinations as the presenting symptom of senile dementia. British Journal of Psychiatry, 161, 263-265.
Dictionary of Hallucinations. J.D. Blom. 2010.