Cognitive and functional neuroimaging correlates for anosognosia in Mild Cognitive Impairment and Alzheimer's disease
Vogel A, Hasselbalch SG, Gade A, Ziebell M and Waldemar G;
Commented by , 21 Apr 2005
Background
Lack of insight and anosognosia are terms used synonymously to describe impaired awareness of cognitive deficits commonly found in Alzheimer's disease. It is known that this is a common symptom, even in the early stages of the disease, though prevalence increases with disease progression.
Frontal dysfunction has been implicated in previous studies, though it is unclear in the literature as to which frontal cortical areas are specifically involved in anosognosia.
Objective
To assess the correlation between anosognosia and
- behavioural symptoms
- executive dysfunction
- frontal cortex regional cerebral blood flow (rCBF)
in patients with mild Alzheimer's disease (AD) and mild cognitive impairment (MCI).
Subjects
Subjects were recruited from a prospective research programme at the Copenhagen Memory Clinic; including all new referrals over 60 with a score of 20+ on the Mini Mental State Examination.
AD and the amnestic form of MCI were diagnosed by defined operational criteria, subjects with co-morbid functional disorders (eg., depression, anxiety, alcohol misuse) were excluded. A control group of subjects matched for age and pre-morbid intelligence was also recruited.
Assessment of subjects included
- full neuropsychiatric examination
- MRI scan
- SPECT scan
- a battery of neuropsychological tests including the Anosognosia Rating Scale, Frontal Behavioural Inventory, and standard frontal lobe tests.
Statistical Analysis
Correlations between anosognosia and cognitive results were assessed for the 3 groups (AD, MCI and controls) using ANOVA, as were differences in rCBF. To assess the impact of rCBF on anosognosia in 6 different frontal cortical regions, stepwise linear regression was used.
Results
On the Anosognosia Rating Scale, 38 % of AD subjects had "full insight", 38 % "shallow insight", 24 % "no insight". For MCI subjects the figures were 40 %, 48 % and 12 % respectively, with no statistical significance between these groups.
The 3 subject groups categorised by "full", "shallow" or "no" insight did not differ in executive functioning or behavioural symptoms, suggesting that executive functions were not directly related to anosognosia. Linear regression found that behavioural symptoms were correlated with anosognosia.
Further analysis of the Frontal Behavioural Inventory scores suggested that disorganisation, apathy, and lack of spontaneity were the abnormal behaviours that correlated most closely with anosognosia.
Using linear regression, rCBF in 6 frontal regions only revealed a correlation between anosognosia and the right inferior frontal gyrus.
Dr Seymour's comments
This study confirmed previous reports that anosognosia (equals impaired insight) is common in both early AD and the amnestic form of MCI and that anosognosia correlates with behavioural symptoms including apathy.
Some previous reports (on subjects with more advanced dementia) have linked executive dysfunction with lack of insight, not confirmed in this study. Therefore, neuropsychological testing of frontal lobe dysfunction in subjects with MCI and early AD do not necessarily imply anosognosia; the authors speculate that executive deficits may be caused by abnormalities in basal forebrain connections to the frontal lobes.
The other main finding of SPECT component of this study was the right inferior gyrus may represent the neurobiological substrate of awareness/insight.
Understanding impaired insight in early Alzheimer's disease is important for clinicians, as it effects how patients and carers understand the illness, and adapt to it.