Recognition memory in Parkinson's disease with and without dementia: evidence inconsistent with the retrieval deficit hypothesis

Parkinson's disease dementia: definitions, guidelines, and research perspectives in diagnosis

Cognitive impairment is common in Parkinson's disease (PD) and involves attentional, executive, visuospatial, and memory dysfunctions. Dementia is more frequently encountered in PD than in age-matched control populations, and whereas operational definitions of Alzheimer's disease and dementia with Lewy bodies have been developed, Parkinson's disease dementia (PD-D) has remained undefined. The Movement Disorder Society developed a task force to define and develop diagnostic guidelines for PD-D. This effort was based on existing descriptive studies with special emphasis on drawing distinction among Alzheimer's disease, dementia with Lewy bodies and PD-related cognitive impairment without dementia whenever possible. The second goal was to provide practical diagnostic procedures to diagnose PD-D. This effort emphasized available bedside tools that do not require neuropsychological expertise to administer or interpret. This work recently has been completed, and two primary articles have been published. The suggested clinical diagnostic criteria for PD-D involve four domains and are anchored in core features, associated clinical features, features that make the diagnosis uncertain, and features that are not compatible with the diagnosis of PD-D. When all four criteria are satisfactorily met, probable PD-D is designated; when the first and last criteria are met, but clinical characteristics are atypical or uncertainty factors exist, possible PD-D is designated. Whereas these definitions are operative and subject to change based on future data, they are based on widely available tests. The inclusion criteria can be applied internationally and in multicenter research on treatment interventions, clinicopathological correlations, and studies of cognitive and other nonmotor elements of PD.

Comparative effects of the dopaminergic agonists piribedil and bromocriptine in three different memory paradigms in rodents

The potential memory-enhancing properties of two dopamine agonists currently used in patients with Parkinson's disease, piribedil (1, 10 mg/kg/day, subcutaneously) and bromocriptine (5 mg/kg/day, subcutaneously), were evaluated in three experiments. Although piribedil (10 mg/kg) and bromocriptine equally enhanced spontaneous object recognition in young adult rats (experiment A), only piribedil displayed beneficial effects against aging-related memory impairments in two radial-maze experiments in mice. First (experiment B), a two-stage paradigm of spatial discrimination was used to assess relational/declarative memory in aged mice; piribedil (1 and 10 mg/kg) selectively and significantly improved the performances of aged mice in the critical tests for relational/declarative memory, whereas bromocriptine had no effect. Second, in a novel working memory task (experiment C), vehicle- or bromocriptine-treated aged mice displayed, compared with (vehicle) younger controls, a severe and persistent deficit in short-term retention of successive arm-visits, performing close to chance whichever the retention interval. Performances of piribedil (10 mg/kg) group remarkably improved across testing-days and reached young adults' level. The restoration of specific mnemonic impairments, in aged mice, highlights the memory-enhancing properties of piribedil. The efficacy of this drug in treating cognitive impairment of Parkinson's disease should now be assessed in more specific models.This work was published in an abstract form: ECNP Abstracts, 2005 (P8060 & P8065).

Clinical diagnostic criteria for dementia associated with Parkinson's disease

Dementia has been increasingly more recognized to be a common feature in patients with Parkinson's disease (PD), especially in old age. Specific criteria for the clinical diagnosis of dementia associated with PD (PD-D), however, have been lacking. A Task Force, organized by the Movement Disorder Study, was charged with the development of clinical diagnostic criteria for PD-D. The Task Force members were assigned to sub-committees and performed a systematic review of the literature, based on pre-defined selection criteria, in order to identify the epidemiological, clinical, auxillary, and pathological features of PD-D. Clinical diagnostic criteria were then developed based on these findings and group consensus. The incidence of dementia in PD is increased up to six times, point-prevelance is close to 30%, older age and akinetic-rigid form are associated with higher risk. PD-D is characterized by impairment in attention, memory, executive and visuo-spatial functions, behavioral symptoms such as affective changes, hallucinations, and apathy are frequent. There are no specific ancillary investigations for the diagnosis; the main pathological correlate is Lewy body-type degeneration in cerebral cortex and limbic structures. Based on the characteristic features associated with this condition, clinical diagnostic criteria for probable and possible PD-D are proposed.

Profile of cognitive impairment in dementia associated with Parkinson's disease compared with Alzheimer's disease

OBJECTIVE

To compare the profile of cognitive impairment in Alzheimer's disease (AD) with dementia associated with Parkinson's disease (PDD).

METHODS

Neuropsychological assessment was performed in 488 patients with PDD and 488 patients with AD using the Mini-Mental State Examination (MMSE) and the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog). Logistic regression analysis was used to investigate whether the diagnosis could be accurately predicted from the cognitive profile. Additionally, the cognitive profiles were compared with a normative group using standardised effect sizes (Cohen's d).

RESULTS

Diagnosis was predicted from the cognitive profile, with an overall accuracy of 74.7%. Poor performance of the AD patients on the orientation test in ADAS-cog best discriminated between the groups, followed by poor performance of the PDD patients on the attentional task in MMSE. Both groups showed memory impairment, AD patients performing worse than PDD patients.

CONCLUSION

The cognitive profile in PDD differs significantly from that in AD. Performance on tests of orientation and attention are best in differentiating the groups.

The ubiquity of memory retrieval deficits in patients with frontal-striatal dysfunction

OBJECTIVE AND BACKGROUND

Previous studies have shown that patients with frontal-striatal dysfunction demonstrate improved performance on tests of recognition memory relative to free recall memory, suggesting deficits in retrieval processes. Not all studies, however, have indicated that all patients with frontal-striatal dysfunction display this profile. In this study, we examined the ubiquity of this "retrieval deficit" profile in a relatively large sample of patients with Parkinson disease (PD) or Huntington disease (HD).

METHODS

Participants included 150 patients with PD and 65 patients with HD. Patients were classified as demonstrating a retrieval deficit or not based on a comparison of their standardized performances on the Recognition Discriminability and Long-Delay Free Recall indices from the California Verbal Learning Test.

RESULTS

Results indicated that 1) a retrieval deficit was more prevalent in patients with HD than PD, 2) this group difference emerged only in patients with at least a mild level of global cognitive impairment, and 3) even when the profile did emerge more frequently in patients with HD, it was present in only 44% of the patients.

CONCLUSIONS

These findings suggest that not all patient groups with frontal-striatal dysfunction display a retrieval deficit profile, but in groups that do (ie, patients with HD), it is more likely to appear in individuals with greater cognitive impairment.