Memory function peaks in our 20s or early 30s and then slowly declines with age, with the greatest changes occurring in speed of processing, memory, and attention. These changes progress across the lifespan with rate of decline beginning to increase in our 60s. Therefore, most individuals will experience a perceivable change in their cognitive function as they age. Cognitive function changes are bothersome and worrisome for many patients, who fear that these changes may represent the start of a dementing illness. For anxious patients, neuropsychological testing can very often help reassure them that the changes they are experiencing are normal for their age and that there are no indications of impairment or a possible dementing illness. For patients who may have experienced a stroke or brain injury that leads to a localized cognitive impairment, neuropsychological testing can help assure them that the cognitive impairment is stable or improving.
Neuropsychological assessment is an essential tool for identifying patients with mild cognitive impairment and for differentiating between types of dementia. The use of neuropsychological assessment for these purposes is well supported by current practice guidelines. As the population of BC ages, physicians will benefit from expanding their expertise with established and developing neuropsychological screening tools, as well as by identifying referral networks which will allow them to access neuropsychologists in their own communities when more comprehensive evaluations are needed.
Neuropsychological assessment can aid in the diagnosis and management of patients with dementia or other psychiatric and neurological disorders. Neuropsychological assessment is the standardized administration of cognitive tests and the individualized interpretation of the results of these tests to form conclusions about brain-behavior relationships and brain function.
Neuropsychologists have extensive training in neuroanatomy, neuropathology, and behavioral neurology following the completion of their doctorate in psychology. Neuropsychologists are trained to interpret the results obtained from standardized neuropsychological assessment measures in the context of a patient’s psychiatric and medical history and to compare that patient’s performance with others of similar age and life experience.
A typical neuropsychological evaluation for a patient with dementia will last 4 or 5 hours, depending on the patient’s tolerance, and will involve standardized testing of memory, attention, processing speed, language, visual-spatial skills, executive functioning, and motor skills. By examining the patient’s pattern of performance on these tests, neuropsychologists can help specify both the type of dementia experienced by the patient and the prognosis.
Neuropsychological evaluations can help develop individualized strategies that the patient and caregivers can use to manage specific deficits. Repeated neuropsychological testing can track the progression of the dementia and can also assess the effectiveness of medications or other rehabilitative strategies.
Neuropsychological evaluation has been recommended by the American Academy of Neurology since 1996 for patients who may have experienced a traumatic brain injury, a stroke, Parkinson disease, multiple sclerosis, a neurotoxic exposure, or dementia. Guidelines published by the American Academy of Neurology note that neuropsychological testing “is particularly valuable in distinguishing between normal aging and mild dementias.”
Common Types of Memory Disorders
Mild cognitive impairment (MCI)
MCI, as described by the Mayo Clinic criteria, is a recently defined condition characterized by cognitive impairments that are apparent on clinical exam or formal cognitive testing, but that are not yet producing a clinically significant impairment in daily functioning. Neuropsychological testing is thus the most common way to diagnose MCI. MCI has been shown to be the strongest predictor for developing dementia. While the strength of this relationship varies somewhat based on setting, patients with MCI seen in specialized settings convert to dementia within 3 years at a rate of 50%. In community settings, both MCI and dementia are quite common and the prevalence of these conditions increases significantly as people age.
Performance on specific types of neuropsychological tests has been found to have strong sensitivity and specificity when predicting which patients with MCI will go on to develop a dementia. For example, patients with amnestic MCI who demonstrate impairments on delayed word-list recall tasks, category-based verbal fluency tasks, and processing speed tasks are at high risk to convert from MCI to Alzheimer's disease
The most commonly used diagnostic criteria for diagnosing Alzheimer disease are those developed by the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA). The NINCDS-ADRDA criteria require that impairment be confirmed by neuropsychological testing. Although the NINCDS-ADRDA criteria are commonly used, they are specific to Alzheimer disease.
Patients with vascular dementia perform better on measures of verbal learning and memory than patients with Alzheimer disease. Patients with Alzheimer disease may have more difficulty generating words of a category than patients with vascular dementia, and patients with vascular dementia may have more difficulty generating words to a given letter than patients with Alzheimer disease.
The frontal-temporal dementias are a cluster of early-onset dementias characterized by significant dysfunction and atrophy in the frontal and temporal lobes. These disorders usually manifest early in the aging process, in the late 50s or 60s, and produce profound impairments in language in the case of the primary progressive aphasias (semantic dementia, non-fluent progressive aphasia) and behavior (frontal-temporal dementia). Individuals with an early frontal-temporal dementia may have an entirely intact ability to learn and remember new material on neuropsychological testing, but may demonstrate significant impairment in speech and language, or significant behavioral change and impairment in executive functioning.As frontal-temporal dementias progress, formal neuropsychological testing of these patients can become challenging because of the severity of their language and behavioral impairments. Consultation with a neuropsychologist about behavior management strategies that family and other caregivers can use to improve care can be useful.
Lewy Body Disease and Parkinsons Disease
Neuropsychological assessment is essential for making the accurate diagnosis among these difficult to distinguish memory dosorders. Lewy body dementia is characterized by significant fluctuations in cognition, particularly attention and alertness, in the context of recurrent well-formed visual hallucinations and parkinsonism. Cognitively, patients with Lewy body dementia typically have significant impairments in visual-spatial processing and form discrimination early in the course of the disease, including problems with constructional apraxia and agnosia.
In patients with Alzheimer disease, these visual-spatial cognitive functions are usually relatively well preserved until later in the course of the disease. Patients with Lewy body dementia may demonstrate fluctuations in attention if assessed across multiple sessions or even one long session, and at times, their fluctuations in consciousness may be of sufficient severity to preclude neuropsychological assessment.
However, it is crucial to note that the risk factors for Alzheimer disease and Lewy body dementia overlap significantly and cases are often co-morbid. Alzheimer disease can produce psychotic symptoms, including hallucinations, suspiciousness, and paranoia. Both disorders can also produce significant disruption in mood and clinically significant anxiety and depression.
Differentiating between these conditions can be challenging. The differential diagnosis of these conditions is further complicated because Parkinson disease also produces a dementia syndrome. Perhaps as many as 40% of patients with Parkinson disease have some cognitive impairment, and perhaps as many as 70% of patients with advanced Parkinson disease have significant cognitive impairment.