Neuropsychology

Dementia is the term used to describe a clinical syndrome of progressive impairment of cognitive functions, often with accompanying changes in behavior and emotion. Many different illnesses can cause the syndrome of dementia. Accurate diagnosis of the particular illness that is likely causing dementia (e.g., Alzheimer's disease, Huntington's disease, Parkinson's disease, fronto-temporal dementia), requires the efforts of a multidisciplinary team of physicians (particularly neurologists and psychiatrists), neuropsychologists, and other health professionals (e.g., social workers). Neuropsychological assessment plays an important role in the clinical identification of the dementia syndrome and the differentiation of various dementia-causing illnesses.

Brief mental status questionnaires can provide health professionals with a quick documentation of the presence of dementia. However, such questionnaires are generally not sufficiently sensitive to detect very mild dementia, particularly in persons who had high intellectual functioning before the onset of their illness. This is due to mental status questionnaires being composed of fairly easy questions. Mental status questionnaires also lack the specificity to assist in differential diagnosis of dementia types, due to the fact that, typically, too few cognitive functions are assessed. In comparison, standardized neuropsychological tests contain a range of task difficulty. This provides for greater sensitivity to subtle or mild cognitive impairment than what is possible through the use of mental status questionnaires.

The ability of neuropsychological test batteries to examine the pattern of performance across different, reliably measured areas of cognitive functioning helps to differentiate dementias caused by particular illnesses. Different dementia-causing illnesses do not manifest with equivalent impairment across all areas of cognitive function. Thus, inspection of the pattern of performance across various neuropsychological tests can be used as an aid to diagnosis. For example, research has demonstrated that Alzheimer's disease typically begins with changes in memory ability that accompany neuronal damage within the hippocampal complex. Neuropsychological tests that assess recall of novel information after a short delay have been shown to be sensitive to these early memory changes. In contrast, regions of the frontal and temporal lobes of the brain are often first affected by the fronto-temporal dementias. Tests of executive functions, including abstract reasoning, problem solving, and the ability to easily shift mental set (readiness to respond in a given manner to a stimulus), are thus most sensitive to the early cognitive changes of fronto-temporal dementia.

It can be difficult to clinically differentiate the early changes of Alzheimer's disease or other dementias from the cognitive impairment that can accompany depression in older adults. Older persons with depression may show deficits on a range of neuropsychological tests, particularly on tests requiring sustained attention or rapid performance, and on tests with pleasant or neutral (in contrast with unpleasant) content. The term pseudodementia was once used to describe persons with depression and cognitive impairment, reflecting the expectation that the cognitive deficits would reverse with effective treatment of the depression. This term is no longer in use because research has shown that many of these persons show a progressive dementia that does not reverse with depression treatment. Such studies have indicated the need for both caution and reassessment in attempts to differentiate cognitive deficits associated with depression from those due to Alzheimer's disease or other dementias.