Evidence for impaired encoding and retrieval memory profiles in Parkinson disease.

OBJECTIVE: The purpose of the study was to determine whether patients with Parkinson disease (PD) demonstrate different memory profiles. Specifically, we sought to ascertain whether the memory performance of PD patients can be categorized as fitting an unimpaired, an impaired retrieval, or an impaired encoding memory profile.
BACKGROUND: Cognitive impairment in PD is usually described as subcortical-frontal in nature. However, neuropathophysiological changes consistent with diffuse cortical disease are also reported. Establishing memory subtypes in PD could potentially assist in reducing the observed heterogeneity of disease presentation, establishing prognosis, making clinical decisions, and defining endpoints in clinical trials.
METHODS: : A sample of 63 PD patients was evaluated with the Hopkins Verbal Learning Test-Revised (HVLT-R). Cluster analysis was used to classify patients into three memory subgroups based on performance on free recall, intrusion errors, and recall enhancement with recognition. Subgroup comparisons were made for demographic and clinical characteristics.
RESULTS: An "unimpaired" group (n = 30) demonstrated intact free recall and few intrusion errors. "Impaired retrieval" (n = 22) and "impaired encoding" (n = 11) subgroups with similar impairment on free recall were also identified, but the impaired retrieval group demonstrated greater memory improvement with recognition (P < 0.001) and had fewer intrusion errors (P < 0.001) than the impaired encoding group.
CONCLUSIONS: A majority of PD patients demonstrate memory impairment, which can be categorized as either a primary retrieval or a primary encoding deficit. Further research is needed to confirm memory subtypes in PD and determine their diagnostic, prognostic, and therapeutic significance.