Neuropsychological assessment of dementia

Abstract

Neuropsychological studies show that cognitive deficits associated with Alzheimer's disease (AD) are distinct from age-associated cognitive decline. Quantitative and qualitative differences are apparent across many cognitive domains, but are especially obvious in episodic memory (particularly delayed recall), semantic knowledge, and some aspects of executive functions. The qualitatively distinct pattern of deficits is less salient in very old AD patients than in younger AD patients. Although decline in episodic memory is usually the earliest cognitive change that occurs prior to the development of the AD dementia syndrome, asymmetry in cognitive abilities may also occur in this "preclinical" phase of the disease and predict imminent dementia. Discrete patterns of cognitive deficits occur in AD and several neuropathologically distinct age-associated neurodegenerative disorders. Knowledge of these differences helps to clinically distinguish among various causes of dementia and provides useful models for understanding brain-behavior relationships that mediate cognitive abilities affected in various neurodegenerative diseases.

Figure 1

Receiver Operating Characteristic curves comparing sensitivity and specificity for the accurate diagnosis of early Alzheimer's disease (AD) achieved with the Trial 1–5 Learning measure from the California Verbal Learning Test (CVLT), the Long-Delay Free Recall measure from the CVLT, the Category Fluency Test (a semantic memory and executive function measure), and Part B of the Trail-Making Test (an executive function measure). The maximally effective cut-point for memory and executive function measures showed excellent sensitivity and specificity in distinguishing between very mild AD and normal aging. (Adapted from Salmon et al. 2002.)

Figure 2

The average composite impairment score achieved by Alzheimer's disease (AD) patients older than age 80 or younger than age 70 in the cognitive domains of language, visuospatial abilities, executive functions, and memory (savings scores). The presented scores are z-scores referenced to the patient groups' respective age-appropriate healthy elderly control cohort. (Adapted from Bondi et al. 2003.)

Figure 3

The mean color-motion integration index scores achieved by normal control (NC) subjects, Alzheimer's disease (AD) patients, and Huntington's disease (HD) patients on a visual sensory integration task. The color-motion integration index reflects the gain in motion direction detection derived from using color information that segments coherently moving targets from distracters. Patients with AD, but not those with HD, were significantly (*) impaired in integrating motion and color information. (Adapted from Festa et al. 2005.)

Figure 4

The average scores achieved by normal control (NC) subjects, patients with Alzheimer's disease (AD), and patients with dementia with Lewy bodies (DLB) on various learning and memory measures from the California Verbal Learning Test (CVLT) and the Wechsler Adult Intelligence Scale-Revised Logical Memory Test. Despite similar levels of global cognitive impairment, the DLB patients were less impaired than the AD patients on measures of retention (memory savings score) and recognition memory (recognition discriminability and recognition accuracy index). PR, percent retained. (Adapted from Hamilton et al. 2004.)

Figure 5

Mean z-scores achieved by patients with Alzheimer's disease (AD) and patients with frontotemporal dementia (FTD; excluding semantic dementia) on the letter fluency and semantic category fluency tests. FTD patients were more impaired on the letter fluency than semantic fluency task, whereas AD patients were more impaired on the semantic fluency than letter fluency task. *p < 0.05, **p < 0.01. (Adapted from Rascovsky et al. 2007.)