Géraud Dautzenberg

General introduction

and show a decline (from a previous level), that is, requiring (minimal) assistance with instrumental activities of daily living (IADL)’. These definitions attempt to create a theoretical yes or no situation or a sharp line on the cognitive continuum. However, in clinical practice, there is a grey area, or rather a rainbow, of interpretation differences. Attempts have been made to categorise this continuum. The DSM 5 uses the words ‘ modest ’ versus ‘ substantial cognitive decline from a previous level of performance in one or more of the domains ’ to capture the difference between not (yet) having dementia (minor Neurocognitive disorder (NCD)/MCI) and patients with dementia in words. An attempt to operationalize this is by stating ‘ test performance in the range of one and two standard deviations below appropriate norms ’ for minor versus ‘ test performance in the range of two or more standard deviations below appropriate norms ’ for major NCD. This translates to a score between the 3rd and 16th percentiles for minor NCD and below the 3rd percentile for major NCD, whereas the (amnestic) MCI was defined to have a delayed recall of 1.5 standard deviations below appropriate norms on a 15-word verbal learning test (Petersen et al. , 1999). One method is to quantify the cognitive continuum by using severity or rating scales. The CDR (0-3) (Hughes et al. , 1982) and GDS (1-7) (Reisberg et al. , 1982) are the most well known (Table 3). This is to (try to) objectify the staging of cognitive impairment/dementia and is used for multiple purposes such as research, renewal of the driving licence, and nursing home allocations.

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Table 3. Rating scales for cognitive impairment. CDR Clinical Dementia Rating Scale

GDS Global Deterioration Scale

CDR0

No cognitive impairment

GDS1 No cognitive impairment GDS2 Age-associated impairment

CDR0.5* Very Mild Dementia

GDS3 MCI

CDR1 CDR2 CDR3

Mild Dementia

GDS4 Mild Dementia

Moderate Dementia Severe Dementia

GDS5 Moderate Dementia

GDS6 Moderate Severe Dementia GDS7 Severe Dementia * In clinical practice, CDR0.5 is often considered as equivalent to MCI but formally, it is already called dementia while this is an exclusion criterion for MCI Another factor in dementia diagnostics is to express the diagnostic certainty in terms of probability. This practice of the Alzheimer diagnostic guidelines of the NIA-AA/NINCDS ADRDA (McKhann et al. , 2011) are spreading to other diagnostic guidelines. The additions

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