Cognitive impairment in patients with Parkinson's disease: diagnosis, biomarkers, and treatment.

Dementia is one of the most common and important aspects of Parkinson's disease and has consequences for patients and caregivers, and has health-related costs. Mild cognitive impairment is also common and frequently progresses to dementia. The underlying mechanisms of dementia associated with Parkinson's disease are only partly known and no mechanism-based treatments are available. Both dysmetabolism of α-synuclein and amyloid-protein and cholinergic deficits contribute to cognitive impairment in Parkinson's disease, and preliminary findings show that imaging and neurophysiological and peripheral biomarkers could be useful in diagnosis and prognosis. Rivastigmine is the only licensed treatment for dementia in Parkinson's disease, but emerging evidence suggests that memantine might also be useful. Whether these or other treatments can delay the progression from mild cognitive impairment to dementia in Parkinson's disease is a key research question.