Anosognosia in Alzheimer's disease: the role of impairment levels in assessment of insight across domains.

Impaired insight for deficits (anosognosia) is common in Alzheimer's disease (AD). However, it has not yet been determined clearly (a) whether different methods for assessing insight are comparable, and (b) whether anosognosia affects different domains to different degrees (domain-specificity). Impaired insight was investigated in 32 patients with AD, who were each accompanied by a caregiver. Anosognosia was assessed by a global clinical rating, questionnaire discrepancies (patient vs. caregiver) covering different domains, and performance discrepancies (self-assessment vs. performance) based on four neuropsychological tests which were compared with those of a healthy control sample. The results of clinical rating and questionnaire discrepancies were closely correlated, but performance discrepancies showed no association with the other methods. Anosognosia was present in the majority of the sample, and occurred across domains. The domains corresponding to core deficits in AD (recent memory, activities of daily living) appeared especially prone to anosognosia. However, results do not suggest that anosognosia itself is domain-specific. Rather, it appears that insight may be invariant, while differences in patient-caregiver discrepancies arise largely from different degrees of deficit across domains.