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Appropriate Diagnosis of Mild Cognitive Impairment: Just What Is “Normal”?

Appropriate Diagnosis of Mild Cognitive Impairment: Just What Is “Normal”?

The topic of appropriate diagnosis of mild cognitive impairment (MCI), which is the focus of the November 2011 issue of the American Journal of Geriatric Psychiatry, is timely given the recently proposed DSM-5 criteria for minor neurocognitive disorders that were tested in the Large Academic Sites Field trials performed by the American Psychiatric Association.1

This is the first time a cognitive diagnosis previously restricted to “pre-dementia populations” will be applied broadly to a variety of neuropsychiatric disorders.

It will be increasingly important to strengthen the definitions of what is “normal” to avoid the “pathologizing” of aging or of any individuals who experience temporary or continuous cognitive impairment.

Defining “normal” memory is becoming increasingly important as the field understands the trajectory for individuals who progress beyond the expected age-associated memory loss and as effective treatments are developed to interrupt the neurodegenerative or cerebrovascular process and thereby improve outcomes. In the 1980s, “normal cognitive decline” had several names, including age-associated memory impairment, age-consistent memory impairment, and late-life forgetfulness. Many potential cognitive problems were dismissed as “senior moments.”1

Our understanding of what is “normal” cognition in the elderly has recently been refined. Considerable data support the validity of MCI, first described 20 years ago. MCI is of interest because subtypes have been shown to predict subsequent development of Alzheimer disease (AD) and other dementing illnesses. In fact, the probability of conversion from MCI to dementia is estimated to be approximately 15%. Estimates of the prevalence of MCI currently range from 5% to 29% and are climbing as the population ages.1

MCI and its subgroups

MCI is defined as cognitive decline that is greater than expected for an individual’s age and educational level, but that does not interfere notably with activities of daily life. The definition has been further characterized by Petersen and colleagues2 and the classification proposed by an international Work Group on MCI. That Work Group defined 4 subgroups:

• Amnestic MCI single cognitive domain

• Multiple cognitive domains (memory plus 1 or more non-memory domains)

• Single non-amnestic (1 non-memory domain)

• Non-amnestic/multiple cognitive domains (more than 1 non-memory domain).

This classification system has been adopted by the NIH’s Alzhei­mer’s Disease Research Centers and provides a common definition for research and clinical care.

The amnestic and non-amnestic MCI subgroups have distinct etiologies and paths of cognitive decline. Recently, the diagnostic categories of MCI have been expanded to include both neuropsychiatric features as well as performance on complex functional activities. These changes are intended to incorporate data that support the mild changes in complex activities of daily living (ADLs) that often are the first signs of MCI. Complex activities or instrumental ADLs include financial management, housework, using a telephone, using public transportation, and shopping for groceries. Neuropsychiatric syndromes (apathy, depression, anxiety, irritability) have also been shown to be common features of MCI and are associated with an increased likelihood of developing AD.

In a comprehensive latent class analysis of 1655 patients enrolled in 29 NIH AD centers, Hanfelt and colleagues3 define 7 empirically based subgroups of MCI based on memory and functional and neuropsychiatric features: 3 are primarily cognitive (either memory problems alone, memory problems with other affected cognitive domains, or a non-amnestic subtype), 3 demonstrate prominent functional and neuropsychiatric disturbances (2 of these subgroups had prominent cognitive deficits and the third showed relatively normal cognitive performance), and 1 subgroup had minimal impairment.

This study reaffirmed that MCI is a heterogeneous syndrome and defines subtypes of MCI according to a common etiology. The authors found that cardiovascular disease (CVD) played an important role in psychopathology contributing to prominent functional deficits and neuropsychiatric symptoms. They hypothesize that CVD is related to neuropsychiatric symptoms based on previous research that CVD is associated with deficits in neuropsychiatric syndromes, including depression and apathy. Further, they hypothesized that patients in CVD subgroups would be more likely to progress to a vascular dementia.

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