Frontal cortical synaptophysin in Lewy body diseases: relation to Alzheimer's disease and dementia.

OBJECTIVES Dementia in Alzheimer's disease correlates closely with loss of neocortical synapses. Similar synaptic loss has been shown in patients whose Alzheimer's disease is also associated with neocortical and brain stem Lewy bodies. The aim was to determine if dementia in Lewy body disease was associated with diminished concentrations of midfrontal cortex synaptophysin. METHODS An immunobinding assay was used to measure synaptophysin in postmortem samples of midfrontal cortex from 89 patients with Alzheimer's disease (ages 59-100, mean 79), 22 with combined Lewy body disease and Alzheimer's disease (ages 69-103, mean 79), 15 demented patients with "pure" Lewy body disease (ages 57-80, mean 74), nine with neocortical and brain stem Lewy bodies who had Parkinson's disease but were not demented (ages 68-85, mean 79), and 20 neurologically normal controls (ages 58-89, mean 75). The diagnosis was confirmed in all cases by detailed neuropathological examination of the contralateral hemibrain. Seven of the patients in the pure Lewy body disease with dementia group had initially presented with parkinsonism and eight with dementia. RESULTS Synaptophysin concentrations (arbitrary units (AU)/microg) in patients with Alzheimer's disease (mean 79 (SD 28)) or combined Lewy body disease and Alzheimer's disease (mean 83 (SD 33)) were significantly lower than in controls (mean 115 (SD 29)) (p=0.002). Synaptophysin concentrations in demented patients with pure Lewy body disease (mean 106 SD 39) and patients with Lewy body disease who were not demented (mean 101 (SD 18)) did not differ significantly from control values or from each other. CONCLUSION Loss of midfrontal cortex synapses probably contributes to dementia in Lewy body disease when Alzheimer's disease is also present but not to the dementia of pure Lewy body disease.