Subjective cognitive decline and progression to dementia in Parkinson's disease: a long-term follow-up study

Introduction: Increasing evidence suggests that subjective cognitive decline is associated with Alzheimer's disease pathology and with an increased risk for future dementia development. However, the clinical value of subjective cognitive decline in Parkinson's disease (PD-SCD) is unclear. The aim of the present work was to characterize PD-SCD and its progression to dementia.

Methods: Forty-three PD patients and twenty normal controls were evaluated with a neuropsychological protocol. Patients were classified as PD-SCD and PD with mild cognitive impairment (PD-MCI). Follow-up assessment was conducted to a mean of 7.5 years after the baseline.

Results: Thirteen patients were diagnosed with PD-SCD (30.2%) and 22 patients were classified as PD-MCI (51.2%) at the baseline. Difficulties in language (60.5%) and memory (51.5%) were the most frequent cognitive complaints. PD-MCI showed alterations in processing speed, executive functions, visuospatial skills, memory and language. No significant differences were found between normal controls and PD-SCD in any of the neuropsychological measures. Conversion to clinically diagnosed dementia during the follow-up was 50% in PD-MCI, 33.3% in PD-SCD and 14.3% in patients without subjective cognitive complaints. Discriminant function analyses and logistic regression analyses revealed that language domain and, especially memory domain are good predictors of dementia.

Conclusions: The present investigation is the first to conduct a long-term follow-up study of PD-SCD and its relationship with the development of dementia. The results provide relevant data about the characterization of SCD in PD patients and show that PD-SCD is a risk factor for progression to dementia.