Dual sensory impairment increases risk for dementia, cognitive decline in elderly patients

Dual sensory impairment in vision and hearing increased the rate of dementia and cognitive decline over the course of a 6-year follow-up period, according to findings from a community-based elderly cohort study published in Neurology.

However, visual impairment alone or hearing impairment alone did not increase rates of dementia and cognitive decline. Results of the study also demonstrated that visual and hearing impairment may result in dementia or cognitive decline regardless of Alzheimer’s disease pathology.

“There are several studies on whether sensory impairments, including vision and hearing impairments, constitute a risk factor for dementia or cognitive decline,” the researchers wrote. “However, studies on [dual sensory impairment] are relatively rare and have produced conflicting results. Most studies had relatively small samples, were cross-sectional in design, used inconsistent outcome variables (different diagnostic criteria for dementia) and simple screening tests [eg, Mini Mental Status Exam, Montreal Cognitive Assessment].”

Additionally, these studies did not examine rates of dementia or changes in neuropsychological scores and were primary conducted in Western countries, with most “focused on white races.” As a result, large-scale studies on the relationship between dual sensory impairment and cognitive impairment in Asians “are lacking,” the researchers wrote.

Gihwan Byeon, MD, of the department of psychiatry at Kangwon National University Hospital in the Republic of Korea, and colleagues examined the impact of single sensory impairment (SSI; visual or auditory) and dual sensory impairment (DSI; visual and auditory) on rates of dementia and longitudinal changes in neuropsychological test scores. The researchers included elderly adults aged 58 to 101 years who represented the general population in the Korean Longitudinal Study on Cognitive Aging and Dementia, a nationwide, prospective, community-based cohort study. They characterized visual and auditory sensory impairment via self-reported questionnaires and analyzed demographic and clinical variables, including cognitive outcomes, every two years over the course of six years. To examine the relationship between SSI or DSI and dementia and changes in neuropsychological scores, the investigators used logistic regression, Cox regression and linear mixed model analyses.

The study comprised 6,520 individuals at baseline, including 932 with normal sensory function, 2,957 in the SSI group and 2,631 in the DSI group. Byeon and colleagues found that, of the three groups, dementia was more common in the DSI group (n = 201; 7.6%). The DSI group also included more men and more participants who were older, as well as lower educational status, lower income, greater comorbid disease, an increased incidence of depression, less social support, greater alcohol intake and rates of smoking, and reduced exercise.

Study data showed that, at baseline, DSI correlated significantly with greater rates of dementia compared with normal sensory function (OR = 2.17; 95% CI, 1.17-4.02), but no such relationship was demonstrated for SSI (OR = 1.27; 95% CI, 0.66-2.41). Over the 6-year follow-up period, the rate of dementia was significantly higher among individuals in the DSI group compared with individuals in the normal sensory function group (HR = 1.9; 95% CI, 1.04-3.46) and neuropsychological scores significantly declined (beta = –0.87; 95% CI, –1.17 to –0.58).

The sensitivity analysis demonstrated that DSI correlated with “a future decline in cognitive function” even among individuals with no prior cognitive decline, according to the study results. Additionally, the subgroup analysis showed that DSI correlated with rates of dementia and cognitive decline in patients negative for the APOE e4 gene, but not in patients positive for the APOE e4 gene. In the analysis using dementia subtype as an outcome (AD vs. non-AD), only baseline prevalence of AD was significantly higher in the DSI group. However, this incidence did not significantly increase during follow-up, according to the study results.

“Depending on the degree of hearing or vision loss, losing function in your senses can be distressing and have an impact on your daily life,” JinHyeong Jhoo, MD, PhD, of Kangwon National University School of Medicine in the Republic of Korea, said in a press release. “But our study results suggest losing both may be of particular concern.”

Future research should examine why individuals with two forms of sensory impairment experienced a greater risk for dementia compared with individuals with one form of sensory impairment, according to Jhoo.

“Older people with only a visual or hearing impairment can usually still maintain social contact, so they may not feel be as isolated or depressed as people who have both impairments,” Jhoo said. “However, when someone has both impairments, that may increase the risk of isolation and depression, which previous research has found may affect dementia risk and thinking skills later on.”