Alzheimer's disease and hallucinations

   Alzheimer's disease is also known as senile dementia of the Alzheimer type (SDAT). Both eponyms refer to the German psychiatrist Alois Alzheimer (1864-1915), who in 1906 was the first to present post-mortem histological findings associated with senile dementia. The German name Alzheimersche Krankheit was coined in or shortly before 1910 by Alzheimer's superior Emil Kraepelin (1856-1926) and included in the eighth edition of the latter's textbook of psychiatry to denote a presenile form of dementia. The relation between Alzheimer's disease, presenile dementia, and senile dementia has been a subject of debate for more than 70 years. Today Alzheimer's disease is conceptualized as a neurological disease characterized by the widespread degeneration of brain cells, together with the formation of neuritic plaques and neurofibrillary tangles, and etiologically linked to the majority of cases included in the general clinical syndrome dementia. The very first case report of Alzheimer's disease, published in 1906 by Alzheimer himself, involves a 51-year-old woman who experienced delusions of jealousy and "auditory hallucinations. The prevalence of hallucinations in individuals with Alzheimer's disease has since been found to vary from 4 to 76%. This broad variation in prevalence rates is commonly attributed to the heterogeneity of the various populations under study, as well as to variations in the different study designs. Among the hallucinations occurring in Alzheimer's disease, the "visual and " auditory ones are the most prevalent; and yet hallucinations in Alzheimer's disease may occur in any of the other sensory modalities as well.

   Their onset, duration, and severity do not seem to follow any identifiable pattern. It has been suggested by some that they fluctuate over time, and by others that they tend to increase over time, as the underlying disease progresses. However, there are authors who report little progressive worsening over time.

   Pathophysiologically, the mediation of hallucinations in Alzheimer's disease is considered to be as diverse as the disease's underlying pathology. It has been suggested that the pre-subiculum and middle frontal cortex play a key role in their mediation, while other authors have maintained that the neurobiological correlates of these hallucinations are non-specific, i.e. they do not differ from those in other diseases associated with hallucinations. Etiologically, the mediation of hallucinations in Alzheimer's disease is associated with direct cerebral damage to the perceptual system, due to cortical and subcortical cell loss, and the presence of neuritic plaques and neurofibrillary tangles. In addition, it has been suggested that these hallucinations can be mediated indirectly by the disturbances in dopamin-ergic, adrenergic, serotonergic, and/or choliner-gic function that frequently occur in individuals with Alzheimer's disease. The disease's characteristic neurocognitive disturbances would seem to play no more than a pathoplastic role in the mediation of hallucinations, although a more prominent role has also been suggested. An important confounder in all studies of hallucinations occurring in the context of Alzheimer's disease is the disorder's comorbidity with conditions such as parkinsonism, metabolic disorders, ocular disease, and hearing loss. The American neuropsy-chologists Robert S. Wilson et al. found that the presence of hallucinations in Alzheimer's disease is associated with an increased mortality rate. The basis of this relation is as yet unknown.

   References

   Alzheimer, A. (1906). Uber einen eigenartigen, schweren Erkrankungsprozess der Hirnrinde. Neurologische Centralblatt, XXV, 1134.

   Alzheimer, A. (1911). Uber eigenartige Krankheitsfälle des späteren Alters. Zeitschrift für die gesamte Neurologie und Psychiatrie,4, 356-385.

   Whitehouse, P.J., Maurer, K., Ballenger, J.F., eds. (2000). Concepts of Alzheimer disease. Biological, clinical, and cultural perspectives. Baltimore, MA: Johns Hopkins University Press.

   Bassiony, M.M., Lyketsos, C.G. (2003). Delusions and hallucinations in Alzheimer's disease: Review of the brain decade. Psychosomatics, 44, 388-401.

   Wilson, R.S., Krueger, K.R., Kamenetsky, J.M., Tang, Y., Gilley, D.W., Bennett, D.A., Evans, D.A. (2005). Hallucinations and mortality in Alzheimer Disease. American Journal of Geriatric Psychiatry, 13, 984-990.