Self-Rated Quality of Life in Mild Cognitive Impairment and Alzheimer's Disease The Problem of Affective Distortion

Background: Cognitively impaired or demented patients may have difficulty performing the complex and multidimensional appraisal required by self-ratings (SR) of quality of life (QoL). Even healthy subjects often refer to their current mood state for QoL self-assessment. Therefore, it is hypothesized that patients rely on current mood state as a reference point for QoL SR, and that the degree of reliance increases with the level of cognitive impairment. Methods: Two consecutive samples of 14 patients with mild cognitive impairment (MCI) and 16 patients with Alzheimer's disease (AD) were examined using the self-rated Dementia-Quality of Life (DEMQoL), a multidimensional mood state questionnaire (MDBF-A, Mehrdimensionaler Befindlichkeitsfragebogen), and the Mini-Mental State Examination (MMSE; MCI: mean = 25.1, SD = 2.1; AD: mean = 20.3, SD = 2.7). Results: As expected, correlations between current mood state and QoL SR (DEMQoL) were highly significant in AD patients but not in MCI patients. The degree of association for all significant correlations was also significantly higher in AD than in MCI patients. Conclusions: The results indicate that SR of QoL are more affectively distorted in AD than MCI. Mood state questionnaires may be an alternative to QoL questionnaires for AD patients, in particular if mood state ratings can be averaged across several points of assessment thus enhancing their validity.