Insight into illness is a critical issue for patient self-report in MCI and AD given that insight into disease effects declines as the disease progresses [87
]. Lack of insight is defined as lack of the ability to elaborate on the experience of a disease, label the symptoms of the disease as pathological, or have knowledge of the deeper effects that the symptoms or disease will have on one's environment [92
]. Anosognosia is defined as unawareness of deficits, specific cognitive dysfunction, and lack of insight [16
]. The terms 'lack of insight' and 'anosognosia' are used largely interchangeably in the cognitive impairment literature.
The relationship of insight to progression in MCI is less clear than it is for AD. For a review of insight in MCI see [95
]. There is currently no consensus on the best method to measure insight. Most methods rely on informant report as a 'gold standard' with patient/informant concordance taken as an indirect measure of patient insight. When the informant is the caregiver, accuracy of report bears critical examination. Caregiver burden, level of depression and anxiety, and caregiver health, including cognitive health, may influence accuracy of caregiver report (for example, [97
Within the AD literature, there has been examination of concordance along with caregiver factors in reporting [17
]. Data on patient/informant concordance and informant accuracy are limited for the milder levels of cognitive impairment. In general, data support an inverse correlation between insight and severity of cognitive impairment and an inverse correlation between patient and caregiver report and severity of cognitive impairment [88
]. Dementia patients likely underestimate their deficits in comparison to caregiver informants [103
], with concordance further reduced as disease progresses (for example, [104
Some empirical reports conclude MCI patients have preserved insight. For example, Farias and colleagues [15
] found that MCI patient self-report was concordant with reports of others, suggesting that MCI patients do not under-report actual deficits in cognition and functioning. Other studies suggest lack of MCI patient insight (see [95
] for a review). Conflicting findings about insight and ability of patients to self-report may be due to different definitions of insight, different definitions of MCI, and/or different methods of measuring insight. Most studies of insight focus on insight for memory functioning; few studies address insight for other cognitive skills, everyday functional abilities, behavior, or affect [95
]. The current literature on insight in MCI is limited by lack of specificity about domains affected, a critical point given evidence of differential insight by domain for MCI patients [91
]. Insight may be well-preserved in some domains across a range of disease severity, but may diminish more rapidly in others [95
]. For example, Clement and colleagues [91
] found that some but not all domains assessed corresponded to performance deficits in global cognitive score and executive functioning for MCI patients, suggesting MCI patients may be aware of general cognitive deficits but not specific memory deficits. To date, the literature on MCI supports the conclusion that insight in MCI is not a single construct and that insight might be spared for some but impaired for other domains (see Roberts and colleagues [95
] for a review).
Evidence suggests that MCI patients may have knowledge of deficits in advance of when deficits are clinically discernible [108
]. Kalbe and colleagues [93
] found that MCI patients overestimate cognitive deficits relative to informants on a 13-domain complaint interview; mild AD patients underestimate their deficits relative to an informant. The validity of the conclusion of 'overestimation' is worth challenging, however, as early cognitive loss may be apparent to the patient but no one else, in part because of the nature of the deficits and in part because MCI patients may actively hide symptoms from others.
To optimize patient self-report, further research is warranted to determine the relationship of insight to level of disease severity, attending to potential differences in insight by domain rather than treating insight as a single global construct. It will be particularly interesting to identify those domains for which patients, especially MCI patients, may have the most accurate view of performance relative to other informants, including clinicians.
Some patient-reported insight scales are presented in Table .