Monoaminergic activities in Lewy body dementia: relation to hallucinosis and extrapyramidal features

Serotonergic (5-HT) and dopaminergic activities have been examined in Lewy Body Dementia (LBD) and compared with Parkinson's disease (PD) and Alzheimer's disease (AD). In the neocortex the LBD subgroup experiencing hallucinations was distinguished from the other categories by an increase in the 5HIAA:5HT ratio measured in frontal cortex and by the serotonergic (5-HIAA or 5-HIAA:5-HT): cholinergic (choline acetyltransferase) ratio in frontal and temporal cortex. In the neostriatum (caudate nucleus), loss of dopamine and increased HVA:dopamine ratio correlated with the reduction in substantia nigra neurons in LBD but not PD, despite the greater loss of neurones and dopamine and the higher dopamine turnover ratio in PD. LBD patients experiencing severe Parkinsonism as a result of neuroleptic treatment tended to have lower neuron counts, in combination with higher turnover ratios, than the remainder. Qualitative differences between LBD and PD included decreased cortical 5-HT turnover in PD compared with the increase in LBD. There were no significant changes in any parameter in AD, with the exception of a reduction in temporal cortex 5HIAA. The results suggest that although the neurochemical pathology of LBD and PD involves similar systems, the nature of the derangements differs sufficiently between the diseases to account for differences in symptomatology.