Parkinson's disease (PD) and
dementia with Lewy bodies (DLB) share clinical and pathological similarities. The defining features are motor
parkinsonism and
cognitive impairment, often accompanied by
visual hallucinations, fluctuating consciousness, autonomic and sleep disturbances, and a number of other non-motor symptoms.
Mild cognitive impairment (MCI) can be identified in 15% of PD patients at time of diagnosis, and may even precede motor symptoms. MCI usually progresses further, and
dementia is a common endpoint.
Cognitive impairment is usually the initial symptom of DLB, and the disease course is severe. A variety of
biomarkers can assist in the diagnosis and prognosis of PD and DLB, including structural and functional imaging, cerebrospinal fluid, and EEG. Compared to the many treatments available for motor symptoms, relatively few systematic studies exist to guide the treatment of
cognitive impairment in PD, and even less in DLB. However, there is good evidence for
cholinesterase inhibitors in both DLB and PD with
dementia, and some indications that
memantine is helpful. Emerging evidence suggest that physical exercise and
cognitive training are also effective, as are some reports of various brain stimulation techniques. Disease-modifying agents that delay the rate of
cognitive decline in PD and DLB are urgently needed.