Summary

Lewy bodies (LB), the pathological hallmark of Parkinson's disease, occur in cortical as well as subcortical areas in the brains of about 10?–30% of patients with dementia clinically consistent with Alzheimer's disease (AD). Lewy body dementia (LBD) overlaps with AD both at autopsy, where most demented patients with cortical LB also have senile and neuritic plaques and to a lesser extent the neurofibrillary tangles typical of AD, and clinically, where patients with LBD generally meet clinical criteria for probable or possible AD. The nosology of LBD and proposed diagnostic criteria therefore need to take cognizance of AD.

A major pathological problem is how many plaques, tangles, or both are required to diagnose AD in the presence of LB. Similarly, since nondemented PD patients also show cortical LB, should LBD be defined pathologically by a threshold cortical LB count? A descriptive and quantitative approach to pathology in well-characterized patients with dementia (AD and LBD), and PD (with and without dementia) is needed.

Clinical criteria for LBD have been proposed and validated in studies that retrospectively reviewed entire case records. Key features are parkinsonian signs, cognitive fluctuations, hallucinations, and a ‘frontalsubcortical’ dementia profile. There are problems in reliably assessing and documenting each of these elements. We suggest a flexible approach that is compatible with published criteria and studies, and includes categories of probable and possible LBD, to help determine which combination of features optimally discriminates LBD from ‘pure’ AD and other dementias.