WHAT IS THE CLINICAL PREVALENCE OF LEWY BODY DEMENTIA

The reported prevalence of Lewy body dementia (LBD) has varied from 12% to 20% in postmortem series. Such series may not be representative of the dementia population as a whole. We have attempted to determine the prevalence of LBD in patients referred to a district general hospital with a diagnosis of dementia. The case notes of a consecutive series of patients with a clinical diagnosis of dementia referred to the care of two consultants in old age psychiatry over a period of 1 year (N = 114) were analysed using a checklist incorporating the items of the criteria proposed by McKeith and by Byrne for the in vivo diagnosis of LBD. The analysis was repeated for the subgroup (N = 76) fulfilling ICD 10 criteria for Alzheimer's disease. The prevalence of LBD was 26.3% according to McKeith criteria, 7% according to Byrne probable and 16.6% according to Byrne possible criteria. There were, however, considerable disagreements between different criteria. The frequencies of individual clinical features within subjects fulfilling and not fulfilling LBD were reviewed. Logistic regression analysis revealed the main clinical features capable of differentiation between LBD and other dementias were: presence of visual or auditory hallucinations; extrapyramidal features or neuroleptic sensitivity syndrome; fluctuating pattern of clinical features over a long period of time (McKeith criteria); and presence of classical Parkinsonism with simultaneous or earlier onset of dementia (Byrne criteria). The results were essentially similar in the Alzheimer's disease subsample. A significant proportion of patients with dementia referred to an old age psychiatry service thus fulfil in vivo criteria for LBD. The variation in frequency of diagnosis of LBD by the different criteria suggests that these clinical criteria may need revising.