Mild cognitive impairment and dementia in early-onset Parkinson's disease: a comparative study by disease duration

BACKGROUND: Few studies have analyzed the frequency of mild cognitive impairment (DCL) and dementia associated with Parkinson's disease (EP) and their relationship with disease duration in early-onset EP (EPIT). OBJECTIVE: To describe and compare the frequency of DCL and dementia in patients with EPIT with short, intermediate, and long disease duration. METHODS: Data from 168 individuals with EPIT were analyzed, classified by disease duration: short (1-8 years, n = 44), intermediate (9-16 years, n = 88), and long (> 16 years, n = 36). Disease duration was defined as the number of years between the first cardinal motor symptom of EP (self-reported and described in the medical record) and the time of assessment. Patients were classified as having normal cognition, DCL, dementia, or cognitive impairment + severe depression. Cognitive test performance and the frequency of cognitive states were compared between groups. RESULTS: There were no significant differences between groups in cognitive performance, except on the clock drawing test. There were also no differences in the various cognitive states. CONCLUSIONS: In patients with EPIT, there were no differences in cognitive performance or the frequency of DCL between groups by disease duration. These findings might indicate that DCL remains stable and that dementia is uncommon in patients younger than 70 years despite a long disease duration; however, longitudinal studies will need to be conducted to confirm the finding.