Wednesday, January 25, 2012

Men More Likely Develop Mild Cognitive Problems - in Neurology, Dementia from MedPage Today

Men are more likely than women to develop mild cognitive impairment (MCI), with and without memory problems, researchers found.

In a cohort of older individuals living in Olmsted County, Minn., about one in every five who was cognitively normal at baseline developed mild cognitive impairment within three or four years, according to Rosebud Roberts, MBChB, of the Mayo Clinic in Rochester, Minn., and colleagues.

Compared with women, men had higher rates of both amnestic MCI -- which involves a memory deficit -- and nonamnestic impairment, which does not, the researchers reported in the Jan. 31 issue of Neurology.

"Differences in incidence rates by clinical subtype and by sex suggest that risk factors for MCI should be investigated separately for amnestic MCI and nonamnestic MCI, and in men and women," they wrote.

In an accompanying editorial, Kenneth Rockwood, MD, of Dalhousie University in Halifax, Nova Scotia, said that "finding a difference between men and women in the incidence of MCI is not a small thing."

"That is because much of the interest in MCI stems from its widely confirmed status as a risk for progression to dementia," he wrote. "Given that women tend to have a higher risk of dementia than do men, and that even in Olmsted County, dementia incidence is similar between men and women, it is unclear how to square more men in the at-risk state not translating into more men with dementia."

To explore the sex differences, Roberts and colleagues turned to the Mayo Clinic Study of Aging, which used data from the Rochester Epidemiology Project to prospectively assess the development of MCI in individuals ages 70 to 89 who were cognitively normal at baseline.

Every 15 months, the participants underwent evaluations that included the Clinical Dementia Rating Scale, a neurologic evaluation, and neuropsychological testing. The analysis included 1,450 individuals who completed at least one follow-up evaluation.

Through a median of 3.4 years, 19.6% of the participants developed mild cognitive impairment and 0.8% developed dementia.

The rate of MCI was higher for men than for women (72.4 versus 57.3 per 1,000 person-years; HR 1.40, P=0.004) and for the amnestic versus nonamnestic subtype (37.7 versus 14.7 per 1,000 person-years).

For both amnestic and nonamnestic MCI, rates were higher for men and for individuals who completed fewer than 13 years of education.

In addition, individuals who were never married were more likely to develop nonamnestic MCI compared with their married counterparts (HR 2.92, 95% CI 1.10 to 7.75).

About one-third of participants who tested positive for MCI at one assessment subsequently tested as cognitively normal.

In his editorial, Rockwood proposed two explanations for the higher rate of MCI among men, even though women have a higher rate of dementia. First, he said, men generally cannot tolerate deficits as well as women.

"While women might have more things wrong at any age, they can live with them longer than men do; for men, deficits more often are fatal," he wrote. "In consequence, the risk of death might be higher for men with MCI, thereby not allowing them to live long enough to develop dementia."

Another possible explanation, though, is a difference between the sexes in how cognition evolves over time.

"Why men have a higher incidence of MCI but a lower incidence of dementia may come about from how they express the later-life dynamics of cognition," Rockwood wrote.

"For some men, MCI represents incomplete disease expression; alternately, they resist dementia development more," he wrote. "In that way, MCI in men could lend some insight into what prevented dementia might look like. Whether this explanation holds depends, as the authors propose, on further investigation of risk factors for MCI separately in men and in women."

Roberts and colleagues acknowledged some limitations of the study, including possible nonparticipation bias and the relatively homogeneous population of Olmsted County (mostly of European ancestry).

http://www.medpagetoday.com/Neurology/Dementia/30851