Cholinergic and other neurotransmitter mechanisms in Parkinson's disease, Parkinson's disease dementia, and dementia with Lewy bodies.

It is now 30 years since the beginning of intensive efforts to understand the neurotransmitter biochemistry of dementia as exemplified by Alzheimer's disease and such studies have led to the development of rational treatment strategies, which are continuing to benefit patients. However, as studies became more sophisticated and clinicians rediscovered an interest in dementia, because of the potential for symptomatic treatment, it has become clear that there are several different neurodegenerative conditions that gives rise to dementia syndromes and that each has distinct neurochemical pathology. This has important treatment implications since what works for one may not work for another or at the extreme, may make matters worse. Therefore it is clear that a detailed understanding of the neurotransmitter function in each condition is not merely academic but can lead to rationale drug design and treatment strategies appropriate for that group of patients. Dementia with Lewy bodies (DLB) has clinico-pathological features, which overlap with either AD or Parkinson's disease (PD) as well as features that help to distinguish it, such as fluctuations in cognitive impairment and a higher prevalence of visual hallucinations. On this basis, it would be expected that the neurochemistry would have some similarities with both disorders.