Dementia with Lewy bodies (DLB) is one of the more common causes of dementia in old age. At present, it is diagnosed on the basis of the presence of characteristic symptoms, of which the most important are visual hallucinations, fluctuations in cognition, and Parkinsonism (movement symptoms like those seen in Parkinson's disease). However, many people who have DLB do not have all of these symptoms, and it can be hard to distinguish from other causes of dementia, especially Alzheimer's disease (AD). It is important to diagnose it accurately because people with DLB can have particularly severe side effects if given antipsychotic medication and, in the long term, so that treatments can be improved. Diagnosis of DLB using clinical symptoms alone has proven in some studies not to be very sensitive, that is cases of DLB are often missed.