LBD is not a single disorder but a spectrum of disorders involving disturbances of movement, cognition, behavior, sleep and autonomic function. LBD includes

• dementia with Lewy bodies (DLB)
• Parkinson’s disease dementia (PDD)

Parkinson's Disease Dementia

Parkinson’s disease (PD) is a common movement disorder that affects 1 in 100 individuals over the age of 60 and 4-5% of older adults over age 85 (approximately 1 million Americans). Original descriptions of PD did not recognize cognitive problems as an important clinical feature. More recently, clinicians have come to realize that PDD occurs often and is among the most debilitating symptoms associated with disease progression. It is estimated that each year up to 14% of PD patients over age 65 will develop at least mild dementia. In one study, almost 80% of PD patients developed dementia over an 8 year period, underscoring the high prevalence of dementia in PD.

Dementia with Lewy Bodies

In the past two decades, a related dementing disorder (DLB) has been described, characterized by signs and symptoms of parkinsonism, fluctuations in cognition and visual hallucinations. Diagnostic criteria derived from the third consensus conference on DLB and published in 2005 were developed with the awareness that many patients with PD develop dementia, usually within ten years of the onset of motor symptoms. Diagnostic criteria for PDD were only recently published in late 2007 and include essentially the same combination of symptoms, catalogued a bit differently. As there are no major clinical differences between DLB and PDD, a somewhat arbitrary diagnostic distinction was affirmed by the DLB consensus authors based on the temporal appearance of motor symptoms and dementia. That is, if motor symptoms precede dementia by more than 12 months, PDD is diagnosed, whereas, if dementia precedes or is concurrent with parkinsonism, then DLB is diagnosed. Because DLB and PDD share many clinical (as outlined in the DLB criteria) and pathological (Lewy bodies) characteristics, both are classified as forms of LBD.