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As individuals age, behaviors often change, but the cause may not be clear. For example, depression and dementia often present similar symptoms on the surface. Neuropsychological assessment, which involves the study of brain-behavior relationships, is an important tool for making a differential diagnosis of psychiatric and neurological disorders.
It utilizes tests that evaluate a broad range of cognitive skills. These include intellectual functioning, attention, memory, problem solving, motor skills, visuospatial abilities and information processing speed. By comparing an individual’s test results to appropriate normative data, a profile can be generated that shows the presence versus absence of impairment, degree of impairment, pattern of impairment and areas of relative strength.
Among the neuropsychological tests used at Saint Luke Institute are the Wechsler Intelligence and Memory Scales and measures of mental flexibility, problem solving and motor function from the Halstead-Reitan Neuropsychological Battery.
Depression in non-demented older individuals can be associated with deficits in many neurocognitive abilities and frequently is an early indicator of the development of Alzheimer’s disease (AD). Since these conditions have radically different courses and outcomes, distinguishing between them is of major importance. AD accounts for 65 percent of dementia, but there are as many as 60 different types, some reversible.
When used with information obtained from clinical interviews and psychological testing, neuropsychological assessment helps to determine if a person has depression, dementia or both. In general, older individuals who present with both depression and neurocognitive impairment are at greater risk for progressing to AD than those experiencing depression alone.
Establishing an early baseline of neurocognitive functioning is very important to help guide future treatment. Approximately 31 to 44 percent of individuals with any type of mild cognitive impairment, defined as cognitive impairment that is greater than expected for an individual’s age and education level, but does not interfere notably with activities of daily life, go on to develop AD.
Temporal orientation (i.e., orientation to person, time, place and circumstance), memory impairment and visual-spatial abilities exhibit differently for someone with AD versus depression.
With major depression, temporal orientation is usually intact or only marginally off, and is likely to be well retained when corrected. With early AD, gross impairment of temporal orientation is fairly common, and much less responsive to correction.
While both depression and the early stages of AD frequently present with memory impairment, qualitative and quantitative differences are recognizable. Immediate learning/retention of verbal information (e.g., a short story) may be similar for the two groups, and be impaired to some extent. However, marked differences usually are evident in the rate of forgetting over time. Providing retrieval cues (e.g., using a multiple choice format when assessing delayed recall) can lead to significantly improved recall in the case of depression, but is of little help when the memory impairment is due to evolving AD.
The types of memory errors made by these two groups also differ. When asked to recognize whether individual words were among a list previously presented, older individuals with major depression are more likely to make false negative errors (i.e., failing to identify words that were a part of the list). Individuals in the early stages of AD are more likely to make more false positive errors (identifying non-target words as having been on the list).
Individuals with major depression typically do not have problems with visual recognition (i.e., recognizing common objects), but it is fairly common with early AD. Likewise, the ability to accurately copy simple and complex drawings typically remains intact with major depression, but is frequently compromised to a substantial degree with early AD.
Neuropsychological testing may also help determine whether a person’s neurocognitive impairment may be reversible by assessing consistency vs. inconsistency within specific neurocognitive domains. An assessment of attention, memory, problem solving, etc. typically includes multiple tests, evaluating various aspects of that domain. Conclusions are based on whether tests within that domain show no evidence of impairment, inconsistent evidence of impairment, or impairment on all or nearly all of the tests in that domain.
The consistency or lack thereof displayed within each individual test is also important. With major depression, the most frequently encountered pattern is inconsistent performance within individual tests and within specific neurocognitive domains. This inconsistency is the by-product of fluctuations in cognitive efficiency caused by a variety of factors, such as mood, affect, motivation, effort, etc. In the early stages of AD, there is less fluctuation within tests, lower overall performance, and selective domains showing prominent impairment on all or most tests.
Since AD is a progressive condition and major depression is not, longitudinal monitoring of neurocognitive status is particularly important in differentiating between them. With major depression, neurocognitive deficits are likely to fluctuate with the changing nature and degree of mood disturbance. When a major depressive episode resolves, prominent improvement in neurocognitive status typically follows. As AD progresses, gradual deterioration occurs over time, initially in the first-affected domains, and eventually in a much broader range of neurocognitive ability areas.
Gary Thompson, Ph.D., is a psychologist and coordinator of neuropsychological services at Saint Luke Institute.
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