MIAMI BEACH—Not all patients with mild cognitive impairment progress to dementia. In fact, among a cohort of patients with mild cognitive impairment who did not progress, the “presence of deficits in multiple cognitive domains was the rule in this group, and not predictive of progression to dementia,” according to Canadian researchers.

The theory that not all patients with mild cognitive impairment progress to dementia arose from the investigators’ experience with long-term clinical follow-up of such patients, explained lead author Christian Bocti, MD, Clinical Instructor of Medicine, Division of Neurology, Department of Medicine at Maisonneuve-Rosemont Hospital, University of Montreal. “Persons who came to our memory clinic with complaints of memory loss—and objective cognitive deficits on formal testing—yet did not fulfill criteria for dementia were followed over time. We simply observed that not all mild cognitive impairment patients are doomed to progress to dementia.”

THE NONPROGRESSORS

To characterize patients with mild cognitive impairment who did not progress to dementia, investigators reviewed the clinical records and neuropsychological data of 25 patients with mild cognitive impairment who did not progress to dementia after a clinical follow-up of 7.7 years. These patients were part of a larger longitudinal study of clinical outcomes in 90 participants with mild cognitive impairment led by Howard Chertkow, MD, at the Jewish General Hospital/McGill Memory Clinic. Of the nonprogressors, 18 had scored 1.5 or more standard deviation points below normal on at least one memory test, and those with mild cognitive impairment who did progress to dementia had “similar distribution of deficits, both for severity and number of cognitive domains affected,” the researchers noted.

According to Dr. Bocti, there are at least three possible explanations as to why some patients with mild cognitive impairment are not likely to progress to dementia. “We found that mild depressive and anxiety symptoms were frequently present in these mild cognitive impairment patients. This could potentially explain some of the neuropsychological findings, and therefore poor performance was not necessarily indicative of underlying early neurodegenerative disease.”

Other factors—use of a small, occasional dose of a benzodiazepine or presence of cerebrovascular risk factors—identified as “potential cognitive confounders” were found in 92% of participants, he noted. However, these factors were felt to be of insufficient severity to explain the initial clinical findings and so did not result in exclusion from the study. Also, Dr. Bocti noted, some of these confounders could contribute to a static cognitive deficit as opposed to a progressive one. “Our cohort is more similar to a ‘real world’ clinical population,” he said. Finally, he proposed that “there could be a group of elderly people who are at the lower end of the normal distribution for cognitive aging, a condition that could represent ‘benign senescent forgetfulness,’ a term first proposed by Kral in 1962. These patients would have a benign course even after many years of follow-up.”

When the research team began the study 12 years ago, the prognosis of these “gray zone” patients was not as well defined, recounted Dr. Bocti. “It was our opinion that mild cognitive impairment represents a group of heterogeneous conditions, and the fact that some [patients with mild cognitive impairment] did not progress did not come as a surprise.” As for how the researchers hope their study data will influence physicians, Dr. Bocti noted, “In this era of increased awareness of cognitive problems in the elderly, there is going to be a tremendous demand on clinicians to assess cognitive complaints at an early stage. We hope that our findings, if confirmed, will provide a more optimistic view of mild cognitive impairment.”

NR

—Heidi Moore

Suggested Reading
Kral VA. Senescent forgetfulness: benign and malignant. Can Med Assoc J. 1962;86:257-260.
Bamford KA, Caine ED. Does “benign senescent forgetfulness” exist? Clin Geriatr Med. 1988;4:897-916.

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