Heterogeneity in mild cognitive impairment: differences in neuropsychological profile and associated white matter lesion pathology

Memory complaints with and without memory impairment: the impact of leukoaraiosis on cognition

White matter alterations, leukoaraiosis (LA) on structural MRI, are associated with cognitive deficits and increased risk of dementia. LA may also impact on subjective memory complaints in otherwise healthy older adults. Little is known about the interplay between LA memory complaints and cognition. We investigated cognitive phenotypes associated with LA in 42 non-demented older adults categorized as having subjective cognitive complaints with no objective cognitive impairment-the subjective cognitive impairment group (SCI; n = 12), amnesic mild cognitive impairment (aMCI; n = 20), or healthy controls (HC; n = 11). We measured LA severity on MRI with a 40-point visual rating scale. Controlling for age and Mini-Mental State Examination (MMSE) score, analyses revealed multiple between-group differences. Follow-up linear regression models investigating the underlying contributors to each clinic group's cognitive profile indicated that LA contributed to learning slope variance (after accounting for age and MMSE) but only for the SCI group. Although the SCI group showed a significantly steeper learning slope when compared to HC and aMCI, increasing LA severity negatively impacted this group's rate of learning. This, in conjunction with the significant contribution of age on SCI learning slope performance variance suggests that greater LA burden at a younger age may contribute to subtle changes in learning for individuals with subjective cognitive complaints.

Verbal serial list learning in mild cognitive impairment: a profile analysis of interference, forgetting, and errors

Using cluster analysis Libon et al. (2010) found three verbal serial list-learning profiles involving delay memory test performance in patients with mild cognitive impairment (MCI). Amnesic MCI (aMCI) patients presented with low scores on delay free recall and recognition tests; mixed MCI (mxMCI) patients scored higher on recognition compared to delay free recall tests; and dysexecutive MCI (dMCI) patients generated relatively intact scores on both delay test conditions. The aim of the current research was to further characterize memory impairment in MCI by examining forgetting/savings, interference from a competing word list, intrusion errors/perseverations, intrusion word frequency, and recognition foils in these three statistically determined MCI groups compared to normal control (NC) participants. The aMCI patients exhibited little savings, generated more highly prototypic intrusion errors, and displayed indiscriminate responding to delayed recognition foils. The mxMCI patients exhibited higher saving scores, fewer and less prototypic intrusion errors, and selectively endorsed recognition foils from the interference list. dMCI patients also selectively endorsed recognition foils from the interference list but performed similarly compared to NC participants. These data suggest the existence of distinct memory impairments in MCI and caution against the routine use of a single memory test score to operationally define MCI.

The role of neuropsychology in prodromal dementia

SUMMARY Before dementia becomes manifest, it is preceded by a long period during which neuropathology exists without clinical symptoms, termed the prodromal stage of dementia (ProD). Owing to its relevance for clinical and research aspects, many efforts are being made to define, diagnose and investigate ProD in greater detail. The ProD state has often been studied in Alzheimer’s disease (AD), whereas less is known about the prodromes of the vascular, extrapyramidal and frontotemporal dementias. Since the operational criteria of ProD are unclear, many studies act on the assumption that ProD and mild cognitive impairment are equivalent concepts. However, owing to several methodological problems with the mild cognitive impairment construct, the viewpoint taken here is that ProD can be understood more profoundly in cohorts of normal elderly subjects. This article discusses the neuropsychological findings of longitudinal, population-based studies, which included elderly, normal subjects, who were followed for years, and made case–control comparisons. Neuropsychological findings clearly revealed deficits in cases (subjects who developed dementia later, mostly AD), which were present already at baseline. Cognitive abnormalities were apparent in the domains of episodic memory, but also in tasks tapping executive, psychomotor and visuospatial functions, attention and naming. Although subtle, these impairments were significant at the group level and often demonstrated deterioration to dementia. Early cognitive deficits of the ProD stage therefore represent markers for the identification of incident AD. It is concluded that neuropsychology is a useful method to screen subjects for ProD at an early time point, when individuals are still normally functioning.

Neuropsychological clustering highlights cognitive differences in young people presenting with depressive symptoms

Early stages of affective or psychotic disorders may be accompanied by neuropsychological changes that help to predict risk of developing more severe disorders. A comprehensive set of neuropsychological measures was collected in 109 help-seeking young people (16 to 30 years; 54 females), recently diagnosed with an affective or psychotic disorder and presenting with current depression. Hierarchical cluster analysis determined three clusters: one deemed to have a "poor memory" profile (n = 40); another with a "poor mental flexibility" profile (n = 38) and a third with widespread difficulties plus "impaired attention and memory" (n = 31). In general, the three clusters were comparable in demographic, functional and clinical factors suggesting some unique role for neurocognitive impairments. A discriminant function analysis confirmed that the clusters were best characterized by performance in "attentional" versus "learning/memory" measures. Furthermore, profiles of independent neuropsychological variables validated the original solution for two of the clusters, distinguishing all cluster-groups on an attentional measure. The findings of this study suggest that despite presenting with very similar levels of current depressive symptomatology, young help-seeking individuals in the early stages of illness have underlying neuropsychological heterogeneity. Distinct neuropsychological profiling may help to predict later psychiatric outcomes and enhance individually-tailored early intervention strategies.

The heterogeneity of mild cognitive impairment: a neuropsychological analysis

A group of 94 nondemented patients self-referred to an outpatient memory clinic for memory difficulties were studied to determine the incidence of single versus multi-domain mild cognitive impairment (MCI) using Petersen criteria. Fifty-five community dwelling normal controls (NC) participants without memory complaints also were recruited. Tests assessing executive control, naming/lexical retrieval, and declarative memory were administered. Thirty-four patients exhibited single-domain MCI, 43 patients presented with multi-domain MCI. When the entire MCI sample (n = 77) was subjected to a cluster analysis, 14 patients were classified with amnesic MCI, 21 patients with dysexecutive MCI, and 42 patients were classified into a mixed/multi-domain MCI group involving low scores on tests of letter fluency, "animal" fluency, and delayed recognition discriminability. Analyses comparing the three cluster-derived MCI groups versus a NC group confirmed the presence of memory and dysexecutive impairment for the amnesic and dysexecutive MCI groups. The mixed MCI group produced lower scores on tests of letter fluency compared with the amnesic MCI and NC groups and lower scores on tests of naming and memory compared with the NC group. In summary, multi-domain MCI is quite common. These data suggest that MCI is a highly nuanced and complex clinical entity.

Use of functional magnetic resonance imaging in the early identification of Alzheimer's disease

A growing body of evidence suggests that a preclinical phase of Alzheimer's disease (AD) exists several years or more prior to the overt manifestation of clinical symptoms and is characterized by subtle neuropsychological and brain changes. Identification of individuals prior to the development of significant clinical symptoms is imperative in order to have the greatest treatment impact by maintaining cognitive abilities and preserving quality of life. Functional magnetic resonance imaging (fMRI) offers considerable promise as a non-invasive tool for detecting early functional brain changes in asymptomatic adults. In fact, evidence to date indicates that functional brain decline precedes structural decline in preclinical samples. Therefore, fMRI may offer the unique ability to capture the dynamic state of change in the degenerating brain. This review examines the clinical utility of blood oxygen level dependent (BOLD) fMRI in those at risk for AD as well as in early AD. We provide an overview of fMRI findings in at-risk groups by virtue of genetic susceptibility or mild cognitive decline followed by an appraisal of the methodological issues concerning the diagnostic usefulness of fMRI in early AD. We conclude with a discussion of future directions and propose that BOLD-fMRI in combination with cerebral blood flow or diffusion techniques will provide a more complete accounting of the neurovascular changes that occur in preclinical AD and thus improve our ability to reliably detect early brain changes prior to disease onset.