Although good epidemiological data do not yet exist, Dementia with Lewy bodies (DLB) is increasingly recognized as one of the most common causes of dementia after Alzheimer's disease (AD). The identification of DLB has important implications in terms of prognosis and patient management. These patients frequently develop motor, psychiatric, and sleep-related disturbances in addition to the dementia syndrome, and information and re-assuring of patients and caregivers are important. In addition, drug treatment of patients with DLB is different from that of AD patients. DLB patients may respond better to cholinergic and dopaminergic agents, but are more likely to develop severe side-effects when treated with anti-psychotic agents, including the atypical ones.

However, diagnosing DLB may be difficult. Several studies have demonstrated a low diagnostic sensitivity compared to AD when using international consensus criteria for a clinical diagnosis of DLB. Thus diagnostic markers are needed to improve diagnostic accuracy. Although emerging data indicate that neuro-imaging techniques such as structural MRI and perfusion SPECT may differentiate AD and DLB at group level, there is too much overlap for these techniques to be useful in the diagnosis of individual patients. Accordingly, the finding that Dat scan can reliably distinguish patients with DLB from those with AD, even DLB patients without parkinsonism, can improve patient management. The most important situation is a patient fulfilling DLB criteria but without parkinsonism, where Dat scan ascertain involvement of the nigrostriatal system typical for DLB. Another potentially important situation is a patient with dementia and parkinsonis and psychosis treated with antipsychotic, where it is unclear whether parkinsonism is secondary to the antipsychotic drug treatment or part of the dementia syndrome. Cases illustrating these clinical dilemmas will be presented and discussed.