Summary

That cognitive decline is a feature of LBD is not disputed. The dispute arises about the type of cognitive decline, whether it has characteristic features that distinguish it from other forms of dementia, its severity and its course. Early case reports include descriptions of a variability of cognition, usually of arousal, in LBD confirmed by larger retrospective clinico-pathological series. Fluctuation in cognitive state either in the form of episodic confusional states resembling delirium or transient periods of reduced or loss of consciousness, superimposed on a background variability is described in 80% of patients in some series. This fluctuation of cognition may be less marked in those LBD cases who most resemble AD.

Some suggest that cognitive abnormality in LBD is milder at onset, and has characteristic features (especially deficits of attention). Others do not confirm these observations. The course of the cognitive decline is variable, a few cases have a rapid onset and decline, the mean durations of illness in most series are between five and seven years. EEG findings, which resemble those of experimental delirium, and neurochemistry in LBD suggest the most likely candidate for the variability in cognition in AD is the relative involvement of the cholinergic and dopaminergic systems. The contribution of cortical Lewy bodies themselves to the cognitive decline is as yet unknown.

Much of the controversy about Lewy body dementia (LBD) arises from the relatively small database and disparity of samples. The same consideration applies to a discussion of cognitive decline in LBD. From the first case reports (Okazaki et al., 1961) dementia has been described in the majority of cases.