The purpose of this study was to provide cutoff scores on the MMSE for the detection of dementia in subjects aged 90 and older stratified according to age and education. The sensitivity and specificity, as well as the overall accuracy, of the MMSE at detecting dementia in the oldest-old were assessed. The current results support making adjustments for age and education when determining cutoff scores for dementia on the MMSE in a sample of people aged 90 and older.
Across all age and education groups, the MMSE demonstrated good overall diagnostic accuracy, as reflected by high AUC values ( and ). The AUC values ranged from a low of 0.82 in the group aged 97 and older with a high school education or less to a high of 0.98 in the group aged 90 to 93 with vocational or some college education. In the group with the lowest AUC, the specificity values were notably lower than in other groups. In those aged 97 and older with a high school education or less, the MMSE is a less-accurate screening tool than for other age and education groups. This may be due in part to a greater proportion of people aged 97 and older with a high school education or less that have some cognitive impairment and were included in the nondemented group. Across all education groups in those aged 97 and older, more participants were CIND than were normal (32% CIND, 25% normal), but in those aged 90 to 93, fewer participants were CIND than were normal (28% CIND, 42% normal). The participants with cognitive impairment of insufficient severity to meet criteria for dementia likely had lower MMSE scores that resulted in more false positives, thus lowering specificity. In an extension of the current study, analyses examining the diagnostic accuracy of the MMSE for identifying CIND in the oldest-old are presently underway with participants of the 90+ Study.
One consistent finding in the scientific literature is that greater age is associated with lower MMSE scores.11–15
The decline in MMSE scores across the later decades of life could be due to a decline in cognition related to benign age-related changes or, alternatively, may result from a higher proportion of cognitively impaired or demented persons in the oldest-old group. Regardless of the cause of age-related changes in MMSE, failure to adjust cutoffs based on age typically results in a loss of specificity.16,17
Given the reported age effects, the cutoff scores for dementia on the MMSE need to be adjusted according to age to maximize the sensitivity and specificity of the scale.18
With advancing age, optimal cutoff scores were expected to decline regardless of educational attainment. Although the optimal cutoffs in this sample did not follow a direct linear trend of lower cutoffs with increasing age across all educational groups, the lowest optimal cutoff score was in the oldest age group. For instance, in the college+group, the recommended cutoff for dementia in those aged 90 to 93 was 25, decreasing to 24 for those aged 94 to 96, and further decreasing to 22 for those aged 97 and older. These downward adjustments were in favor of preserving specificity. Keeping the same cutoff of 25 for those aged 94 to 96 and 97 and older in the college+group would have lowered the specificity from 0.80 to 0.74 and 0.58, respectively. The decline in specificity with increasing age was similarly noted in findings from the Canadian Study on Health and Aging (CSHA).17
When using a cutoff of 24 in the CSHA sample, sensitivity was higher and specificity was lower in those aged 80 to 89 (sensitivity=0.95, specificity=0.82) than in those aged 65 to 79 (sensitivity=0.82, specificity=0.86). Age-adjusted cutoffs for the MMSE may help preserve specificity, thus allowing for accurate screening of dementia for elderly patients even into their 90s.
The unexpected finding of lower optimal cutoffs for younger participants found in the group with vocational school or some college education (22 for aged 90–93, 25 for aged 94–96, and 24 for aged ≥97) may be due in part to the number of specific MMSE scores represented in each subgroup. Subjects aged 94 to 96 had a more evenly distributed number cutoff scores (e.g., 2 participants with a score of 23, 1 participants with a score of 24, and 3 participants with a score of 25), whereas those aged 90 to 93 had one participant with a score of 23, no participant with a score of 24, and seven participants with a score of 25. Given the small sample sizes in the subgroups, these variations in represented scores possibly influenced the sensitivity and specificity estimations. Regardless of chosen cutoff scores, the group aged 90 to 93 had higher specificity than those aged 94 to 96 and 97 and older in the group with vocational school or some college education, in keeping with the trend of the other age-by-education groups in this sample. Therefore, age-adjusted cutoffs are likely to be useful when using the MMSE with subjects aged 90 and older
Along with older age, lower educational level is associated with lower MMSE scores.13,15,19,20
Education-adjusted cutoff scores generally are thought to reduce the risk of misclassification bias in screening for dementia.21
Adjusting the MMSE cutoff for dementia to a lower cutoff score in patients with less education would help preserve specificity.
Results from the present study did not show a clear advantage for lowering the cutoff point for participants with less education. In the group aged 90 to 93, for example, the best balance between sensitivity and specificity occurred at a cutoff of 23 for participants with a high school education or less, decreased to a cutoff of 22 for those with vocational training or some college, and increased to a cutoff of 25 for those with a college education or higher. Furthermore, in the group aged 97 and older, the cutoff for the ≤HS and college+groups was the same when considering the best sensitivity versus specificity trade-off, whereas the optimal cutoff for the vocational school or some college group was higher. The unexpected variation in cutoffs for the vocational school or some college educational group in relation to the ≤HS and college+groups possibly reflects the heterogeneity of the vocational school or some college group. It is possible that those who attended vocational school are different from those who attended some college in a manner that would affect cognitive test performance, but the present data set does not allow a separation of the two groups for further analyses. Results from this sample suggest that education-adjusted cutoffs in those aged 90 and older may not be as useful as age-adjusted cutoff scores because of the variation seen in the vocational school or some college group. Furthermore, the small number of participants in this sample having a high school education or less precluded further analyses across a lower range of educational achievement.
Several caveats must be considered when evaluating these study results. First, the neurology examiners observed the administration of the MMSE items during participants' evaluations. As such, a participant's performance on the MMSE may have influenced the dementia diagnosis. This is unlikely to have significantly affected the outcomes, because the final MMSE score was not shared with the neurological examiner until after the entire protocol was completed and a diagnosis had already been assigned. Furthermore, the MMSE data were used within the context of a much longer neurological examination that included additional mental status assessment. Finally, no predetermined MMSE cutoff scores were used in the neurologist's diagnosis of dementia.
The second caveat relates to the generalizability of these findings for persons with low educational attainment. This sample represents a highly educated group of the oldest-old. Ninety-one percent of participants had completed at least high school, compared with approximately 53% of the general U.S. population in the same age cohort.1
Optimal cutoffs for the oldest-old with a grade school education may be lower than those demonstrated with this sample.
This study has several strengths. It included a large number of subjects aged 90 and older, ranging from 90 to 104. This allowed a more-detailed analysis of age-related cutoff points than is currently available in the literature. In addition, the availability of a neurological diagnosis, including CIND, allowed reasonable inferences to be made as to the effect of a higher proportion of subjects aged 97 and older with a CIND diagnosis potentially affecting the specificity of the MMSE as a screening tool. Also, by presenting MMSE cutoff scores for dementia across the tenth decade, this study expands the usefulness of a tool that is already in widespread use in research and clinical practice.
The oldest-old are the fastest growing segment of the population, and having age-appropriate cutoff scores for screening measures such as the MMSE provides useful tools for the accurate screening and further treatment of cognitive dysfunction in these patients. The MMSE appears to be an accurate instrument for dementia screening in subjects aged 90 and older. To preserve a balance between sensitivity and specificity, suggested cutoff values on the scale were adjusted downward for older subjects and those with less education. Based on findings from the present study, age- and education-related adjustments should be considered when using the MMSE with patients who are aged 90 and older.