Mild cognitive impairment in Parkinson's disease: Diagnosis and progression to dementia

Mild cognitive impairment is common in nondemented Parkinson disease patients (PD-MCI) and is considered as a risk factor for dementia (PDD). Recently, the Movement Disorder Society (MDS) published guidelines for PD-MCI, although the studies available are still limited. The aim of this work was to characterize PD-MCI and its progression to dementia. Moreover, the study variables could be considered as predictors for the progression of cognitive impairment.

The study included 43 patients with idiopathic PD (mean age = 59.19 years, SD = 9.64) and 20 healthy and neurologically normal controls (mean age = 60.85 years, SD = 12.26). The criteria proposed by the MDS Task Force were applied for the PD-MCI diagnosis. Follow-up assessments were conducted within six to eight years after the diagnosis of PD-MCI.

The results showed that 60.5% of the patients were diagnosed with PD-MCI when a comprehensive assessment was performed (MDS criteria Level 2), while 23.3% of the patients met MCI criteria when a brief assessment was used (MDS criteria Level 1). Multiple domain impairment was the most frequent impairment (96.2%). A total of 42.3% of PD-MCI patients had dementia in the follow-up study. Logistic regression showed that the Hoehn and Yahr stage and education significantly contributed to the prediction of PD-MCI. Moreover, the Hoehn and Yahr stage and memory domain significantly contributed to the prediction of dementia.

The results of the study: (a) provide relevant data about the process of validation of the MDS PD-MCI criteria, (b) reinforce the hypothesis that PD-MCI is more frequent than previous studies showed without applying MDS criteria, and (c) confirm that PD-MCI is a risk factor for the onset of dementia. Finally, the study shows that neurological impairment, educational level and memory impairment were predictors for the progression of cognitive impairment.