Dementia, of which Alzheimer disease (AD) is the most common cause, is a major health problem confronting contemporary society. Because prompt (and, in the future, possibly preclinical) initiation of treatment offers the greatest hope for the successful management of AD, early diagnosis is essential.
Short of mass screening of the elderly using a neuropsychological test or some yet-to-be-determined biomarker, persons with cognitive disorders come to the attention of the health care system only when symptoms are recognized. Occasionally, physicians identify cognitive deficit on routine examination or when they notice patients having trouble following instructions (eg, taking medications properly). In most cases, it is left to the patient or a family member or close friend of the patient to note the problems in cognition, memory, or behavior and report them to a health care provider. Thus, what might be termed "cognitive complaint" is a critical issue in dementia care. It determines, to a large extent, the timeliness of evaluation, diagnosis, and treatment.
EARLY AD OVERLOOKED
Unfortunately, delay in diagnosis and treatment is common. In a recent clinical trial that focused on very mild, early-stage AD in which a criterion for admission was diagnosis within 1 year of the start of the study, the mean estimated duration of dementia at entry into the study was almost 3 years.1 A major reason for the delayed diagnosis of AD, in general, is lack of awareness of cognitive problems on the part of patients and family members. For the latter, the delay in recognizing deficits in kin is often the result of simple psychological denial; for patients, it is more likely evidence of anosognosia, part of the brain disease itself. Some patients with AD flatly deny the existence of flagrant cognitive disabilities; others acknowledge a problem but minimize its significance, or their actions suggest that they do not fully appreciate the implications.2
MILD COGNITIVE IMPAIRMENT
Once AD is clinically manifest, it unfortunately may be too late to significantly influence the subsequent course of the disease. Preclinical detection and treatment are therefore the ideal.3 The population at maximum risk for AD—and for whom such intervention strategies should be targeted—are persons with mild cognitive impairment (MCI). This condition, which is intermediate between normal cognition and dementia, is characterized by significant cognitive deficit, most often in the domain of memory, but with satisfactory social and occupational functioning.4 More than 50% of persons with MCI—especially those with the amnestic subtype—will convert to frank dementia, usually AD, within 5 years.5
A diagnostic criterion for MCI has been cognitive complaint on the part of the patient, an informant, or both,6 but if AD is destined to develop in many persons with MCI and if AD involves some degree of anosognosia, then patients with MCI also might be expected to be less than fully aware of their symptoms. Indeed, Tabert and colleagues7 showed that patients with MCI with diminished awareness of their (comparatively minor) cognitive deficits were more likely to progress to dementia than were those who were more aware.
Other studies, using different experimental designs, also show the existence of anosognosia in MCI.8 It is for this reason that some authors9-11 advocate dropping "subjective memory complaint" (at least on the part of the patient) from the diagnostic criteria. In contrast, other studies suggest that while mild AD involves some degree of anosognosia, most patients with MCI are still capable of recognizing their deficits.12
As illustrated by Case in Point: Mild Cognitive Impairment, the issue of impaired self-awareness in MCI remains ambiguous. In fact, different ways of treating cognitive complaint as a diagnostic criterion for MCI probably account for some of the major differences between studies regarding the prevalence of MCI and its rate of progression to dementia.
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