Prospective memory in Parkinson's disease: the role of the motor subtypes.

Background: Prospective memory (PM) is defined as memory for future intentions and it is typically divided into time-based and event-based PM. Deficit of PM has been reported in patients with Parkinson's disease (PD) but no study has yet explored the association between motor subtypes (tremor dominant and rigidity/bradykinesia dominant) and performance on PM tasks. The aim of the study was to explore the role of motor subtypes in the defect of PM.

Methods: Consecutive outpatients with tremor dominant (TD-PD) or rigidity/bradykinesia dominant (PIGD-PD) PD and healthy subjects (HCs) were enrolled and underwent a neuropsychological battery assessing PM, verbal memory and executive functions and questionnaires assessing apathy, functional autonomy, and perceived memory disturbances.

Results: We enrolled 28 patients with TD-PD, 28 patients with PIGD-PD and 50 HCs. The three groups did not differ on demographic and cognitive variables. Patients with TD-PD performed worse on time-based PM tasks than patients with PIGD-PD and HCs; no significant difference was found among the three groups on event-based PM tasks. Executive dysfunctions contributed to reduced time-based PM scores in TD-PD. Moreover, severe deficit of time-based and more frequency of perceived failures of PM contributed to reduced functional autonomy in TD-PD.

Conclusion: The finding of a poorer performance of patients with TD-PD than ones with PIGD-PD and HCs suggests a selective deficit of time-based PM abilities in TD-PD group; therefore, deficit of time-based PM might be considered as a distinctive non-motor symptom of TD-PD and it might affect the functional autonomy in this subtype of PD.