Mild cognitive impairment exists in Parkinson's disease.

Cognitive impairment exists in Parkinson's disease (PD) as a transitional state between cognitively intact and demented PD patients. It seems to be a risk factor for the development of dementia in PD, but the precise criteria and unfavorable cognitive profile of mild cognitive impairment in PD (MCI-PD) have not yet been established. The concept may turn to be different from that in Alzheimer's disease since we search for those already diagnosed PD patients who are at risk of developing dementia. In addition, clinical variables specific for PD also play role. Importantly, MCI possesses a metabolic basis in PD. Various biomarkers particularly including neuropsychological testing and the brain imaging hold promise in identification of MCI-PD patients with unfavorable prognoses. Well-designed longitudinal studies in MCI-PD cohorts are needed to assess the sensitivity and specificity of the PD-MCI designation as far as dementia development is concerned.