PHILADELPHIA—Cognitive decline in highly intelligent elders is particularly difficult to diagnose, as they tend to score too high on cognitive and memory tests, according to Dorene M. Rentz, PsyD. Despite the utility of detecting mild cognitive impairment in the early stages of Alzheimer’s disease, the work of Dr. Rentz and colleagues suggests that high-functioning, intelligent elders are often overlooked by standard, established criteria for mild cognitive impairment. Dr. Rentz is an Instructor in Neurology at Brigham and Women’s Hospital, Harvard Medical School, Boston.

“The high cognitive reserve of these elders would mask early changes on testing for many years, prohibiting diagnosis until long after the pathologic process has commenced,” Dr. Rentz suggested. In previous research, Stern et al have shown that highly educated elders tend to have the greatest pathologic burden and the shortest time between diagnosis of Alzheimer’s disease and death. “Based on this data,” she continued, “we believe that high-functioning elders are among the most at risk for not receiving early treatment intervention.”

In order to see whether IQ-adjusted cognitive test norms can predict early cognitive decline more accurately, researchers followed 42 highly intelligent elders (mean age, 70; mean IQ score, 125) for approximately four years. The researchers measured IQ with the American National Adult Reading Test rather than educational level in order to avoid missing those who did not have educational opportunities due to financial hardship, wartime constraints, or sex. “In fact, many highly intelligent women in our sample chose marriage and family over college,” Dr. Rentz noted.

ADJUSTING FOR INTELLIGENCE

At baseline, all elders scored in the normal range for their age across all cognitive tests on the basis of published test norms. When the test norms were adjusted for high intelligence, 22 elders continued to score normally within this IQ-adjusted range and were predicted to remain stable. Nine elders showed initial deficits in attention by IQ-adjusted norms and were also predicted to remain stable. Eleven elders had memory deficits greater than two standard deviations from the IQ-adjusted norm and were predicted to decline over time.

After approximately four years, six of the 11 elders that were predicted to decline met established criteria for mild cognitive impairment, Dr. Rentz reported at the 53rd Annual Meeting of the American Academy of Neurology. Three of the 31 elders predicted to remain stable had declined. “After four years, the odds of developing mild cognitive impairment using IQ-adjusted norms [were] 12.2 times greater than the odds of developing mild cognitive impairment in those not predicted to decline,” Dr. Rentz said.

The 11 elders that were predicted to decline had significant changes in naming, total recall, delayed recall, 30-minute delayed recall, and visuospatial functioning in a pattern consistent with Alzheimer’s disease. Scores in category and letter fluency, however, did not change.

COGNITIVE DECLINE AMONG THE INFLUENTIAL

As new drugs that slow or halt the disease progression become available, early diagnosis should take into account an individual’s cognitive ability level, Dr. Rentz said. “Failing to do so places a critical segment of older adults, namely at-risk elders who may be making a significant contribution to society, at a greater disadvantage in terms of receiving early treatment intervention,” she concluded.

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