Global measures: utility in defining and measuring treatment response in dementia

Abstract

Global measures used in treatment trials in dementia encompass two distinct categories: (1) clinician's interview-based global severity scales, and (2) clinician's interview-based global change scales.

The global severity scales that have been used include: the Clinical Dementia Rating (CDR) and the related CDR-sum of boxes (CDR-SB), the Global Deterioration Scale (GDS), and the Functional Assessment Staging (FAST) procedure. The global severity scales are clearly useful in subject categorization in treatment trials, in part because they are relatively free of many of the sociocultural biases inherent in mental status and psychometric descriptors. Global severity scales can also be used to demonstrate therapeutic efficacy in terms of the general progression of the dementia process. These measures have also proven to be useful in sensitively assessing pharmacotherapeutic effects in Alzheimer's disease (AD) treatment trials. For example, in pivotal trials: (1) in Mild to Moderate AD, the GDS has shown significant change in response to medication, whereas the results on the Mini-mental State Examination (MMSE) were not significant, and (2) in Moderate to Severe AD, the FAST has shown significant pharmacotherapeutic efficacy, whereas the results using the MMSE were not significant.

The global change scales employed in dementia trials differ widely in assessment methodology. Clinical Global Impressions of Change (CGIC) scales do not have defined methodologies, whereas Clinician's Interview-Based Impression of Change Plus Caregiver Input (CIBIC-Plus) scales are much more elaborate. The CIBIC-Plus procedures require an independent clinician assessment and can provide independent, comprehensive evidence of therapeutic efficacy. The CIBIC-Plus procedure may also be useful in sensitively assessing efficacy in future prevention trials, for example in subjects with Subjective Cognitive Impairment. For Mild Cognitive Impairment (MCI), global severity scales already appear to be one modality for the sensitive assessment of change. The CIBIC-Plus procedures might also productively be applied in future MCI therapeutic trials.