Use all information available and make the best judgment. Score each category (M, O, JPS, CA, HH, PC) as independently as possible. Mark in only one box, for each category, rating impairment as decline from the person’s usual level due to cognitive loss alone, not impairment due to other factors, such as physical handicap or depression. Occasionally the evidence is ambiguous and the clinician’s best judgment is that a category could be rated in either one of two adjacent boxes, such as mild (1) or moderate (2) impairment. In that situation the standard procedure is to check the box of greater impairment.
Aphasia is taken into account by assessing both language and non-language function in each cognitive category. If aphasia is present to a greater degree than the general dementia, the subject is rated according to the general dementia. Supply evidence of non-language cognitive function.
The Global Clinical Dementia Rating (CDR®) Score is derived from the scores in each of the six categories (“box scores”) as follows. Memory (M) is considered the primary category and all others are secondary. CDR = M if at least three secondary categories are given the same score as memory. Whenever three or more secondary categories are given a score greater or less than the memory score, CDR = score of majority of secondary categories on whichever side of M has the greater number of secondary categories. When three secondary categories are scored on one side of M and two secondary categories are scored on the other side of M, CDR=M.
When M = 0.5, CDR = 1 if at least three of the other categories are scored one or greater. If M = 0.5, CDR cannot be 0; it can only be 0.5 or 1. If M = 0, CDR = 0 unless there is impairment (0.5 or greater) in two or more secondary categories, in which case CDR = 0.5.
Although applicable to most Alzheimer’s disease situations, these rules do not cover all possible scoring combinations. Unusual circumstances occur occasionally in Alzheimer’s disease and may be expected in non-Alzheimer dementia as well are scored as follows:
- With ties in the secondary categories on one side of M, choose the tied scores closest to M for CDR (e.g., M and another secondary category = 3, two secondary categories = 2, and two secondary categories = 1; CDR = 2).
- When only one or two secondary categories are given the same score as M, CDR = M as long as no more than two secondary categories are on either side of M.
- When M = 1 or greater, CDR cannot be 0; in this circumstance, CDR = 0.5 when the majority of secondary categories are 0.
Morris, J.C. (1993). The clinical dementia rating (CDR): Current version and scoring rules. Neurology, 43(11), 2412-2414.