Qualitative performance characteristics differentiate dementia with Lewy bodies and Alzheimer’s disease

Accurate and early clinical diagnosis of dementia with Lewy bodies (DLB) is essential for optimal management so that pitfalls such as severe neuroleptic sensitivity can be avoided, a trial of cholinesterase treatment can be instigated, and parkinsonian symptoms can be appropriately treated, weighing up the balance of psychiatric and motor symptoms and fall risk. In practice it has often been difficult to differentiate DLB from other forms of dementia, particularly Alzheimer’s disease. Several previous studies have suggested that DLB and Alzheimer’s disease can be differentiated on the basis of visual and visuospatial tasks. The tasks most easily applicable to initial diagnosis are drawing tests (such as the clock drawing). However, this approach ignores what is one of the more striking features of DLB: fluctuating cognition. Operationalised criteria for the clinical diagnosis of DLB (which do consider a broad range of symptoms) have achieved high levels of specificity (> 90%); in many studies sensitivity has been as low as 50%. Probably the major obstacle to accurate diagnosis has been the difficulty of identifying fluctuating cognition; for example, two inter-rater reliability studies have indicated that agreement