Evidence is mounting that hearing loss in older patients is not just a relatively benign condition that, at its worst, leads to frustrated family members who can’t make themselves heard. Research by at least two independent groups has shown a strong association between hearing loss and cognitive decline. The results are troubling enough to cause one investigator to call for an all-hands-on-deck push to make age-related hearing loss a public health priority.
“In terms of the strengths of the findings, we’re not talking about a 20 percent or 40 percent increase; the two- to five-fold higher rate of dementia we’ve documented in one study is just a huge effect,” said Frank R. Lin, MD, PhD, an assistant professor in the division of otology, neurotology and skull base surgery at Johns Hopkins School of Medicine, assistant professor in the division of geriatric medicine in the Johns Hopkins Center on Aging and Health and assistant professor in the departments of epidemiology and mental health at the Johns Hopkins Bloomberg School of Public Health in Baltimore. “My collaborators at the NIA [National Institute on Aging] were very surprised at the strength of the association.”
Dr. Lin’s research has been supported by a Triological Society/American College of Surgeons Clinical Scientist Development Award, a National Institute on Deafness and Other Commucations Disorders/National Institutes of Health Career Development Award and the Elearnor Schwartz Charitable Foundation.
Given the rapidly aging population and the shortcomings of current hearing-loss therapy, “this is an under-recognized issue that has to be addressed,” said Dr. Lin.
The study in the NIA-sponsored Baltimore Longitudinal Study of Aging was one of Dr. Lin’s first to show such a strong link between hearing loss and dementia (Arch Neurol. 2011;68:214-220). The study included 639 participants, most of whom were between 60 and 80 years of age. At baseline, none of the participants had any evidence of cognitive impairment, although some had hearing loss. During a median follow-up of 11.9 years, 58 cases of incident all-cause dementia were diagnosed, of which 37 were considered to be Alzheimer’s disease. The risk for participants developing dementia “increased linearly with the severity of hearing loss,” Dr. Lin said. Compared with normal hearing, the hazard ratio (risk) for dementia was 1.89 (1.00–3.58) for mild hearing loss, 3.00 (1.43–6.30) for moderate hearing loss and 4.94 (1.09–22.40) for severe hearing loss. These results were supported by a subsequent study of nearly 2,000 patients (JAMA Intern Med. 2013;173:293-299), and in another study by an independent study group in the U.K. (Neurology. 2012;1583-1590).
An argument could be made that some other, yet-to-be-determined physiologic factor may serve as a common cause for both hearing loss and dementia. But Dr. Lin believes that the strength of the epidemiologic evidence suggests otherwise. “If we saw a relatively small effect, it would be logical to dismiss the link between hearing and cognition as just being part of some natural aging process or from unaccounted cardiovascular risk factors. But when you see that strong of a link, it’s unlikely that any degree of confounding by other physiologic risk factors could fully argue away that effect,” Dr. Lin said. “Clearly, something else is going on.”
What Interventions Work?
Dr. Lin acknowledged that a key question remains: Can cognitive declines be reduced by hearing aids and other rehabilitative interventions? “Scientifically, we just have no clue,” he said. “It may be that those interventions are too little, too late. However, from a clinical standpoint—based on my own practice experience—these interventions, whether a hearing aid or cochlear implant, do seem to make a difference.”
He cited the example of an older patient with age-related hearing loss whom he typically treats with hearing aids or other assistive devises and ongoing rehabilitative hearing therapy. “Fairly quickly, you can see the difference in the lives of patients who are treated this way,” he said. “All of a sudden, they are able to engage again; they are no longer isolated. These really can be dramatic effects but, of course, this is just base on clinical impression right now.” He did point out, however, that earlier researchers have made a connection between social isolation, cognitive load and cognitive function (Psychol Aging. 2009;24:761-766).
The next step in Dr. Lin’s research is to investigate whether hearing-loss interventions could in fact reduce the risk of cognitive decline and dementia. “We’ve just submitted a grant to carry out this definitive clinical trial,” he said. The trial will randomize half of a group of older patients with hearing loss to treatment and half to watchful waiting. “Assuming that hearing loss treatment could have even a modest effect on helping reduce cognitive decline, this could be a seminal study that will finally give this issue the degree of public health urgency that it truly deserves.”
To increase awareness about hearing loss and its effects on dementia, Dr. Lin recently began working with the Bloomberg School of Public Health to raise funds for a Center on Hearing and Healthy Aging (see “Multidisciplinary Initiative Seeks to Improve Age-Related Hearing Loss Treatment,” below).
Dr. Lin said he is not surprised by the fact that making hearing loss in older patients a public health focus is proving to be such a challenge. “Fifty years ago, there was a great deal of evidence that smoking was bad for you…. What finally changed was two generations of constant public health badgering, with cigarette ads banned from television and magazines, smoking taken off of movie screens and educational initiatives started in our schools—all of those things were needed to change perception and behavior over time.”
Dr. Lin gave another example—one that actually holds some hope for a more rapid uptake of the message regarding hearing loss in older patients. In the early 1990s, he noted, isolated systolic hypertension was routinely ignored, because the condition was a very common part of aging, thought to be benign. Then a large randomized controlled trial showed that treating the condition with diuretics lowered the risk for strokes by more than 40 percent, “and fairly quickly, it became the standard of care,” he said (JAMA. 1991;265:3255-3264).
Dr. Lin said that if clinicians could view hearing loss in older adults with the same degree of urgency as smoking and isolated systolic hypertension, then the condition would soon become more of a priority. Or perhaps an even stronger paradigm shift is needed—viewing age-related hearing loss as though it were the pediatric variety. “We all know the data showing a strong correlation between hearing and the development of learning and social skills in kids,” he said. “And so we act accordingly, with aggressive screening and treatment. Where are the similar efforts for our older population?”
Craig A. Buchman, MD, chief of the division of otology, neurotology and skull base surgery, department of otolaryngology-head and neck surgery at the University of North Carolina at Chapel Hill, agreed that, because pediatric screening and treatment programs are better developed in children than those in adults, “it stands to reason that there is a great opportunity for improvement in the elderly.”
Dr. Buchman also echoed Dr. Lin’s concerns about the lack of urgency and attention that has stalled such efforts. “Hearing loss among adults is definitely an under-appreciated problem,” he said. “It has the potential for having a serious negative impact on both cognitive and psychosocial functioning, economics and quality of life.” Thus, “broad messaging and adult screening are needed to help better identify affected and at-risk individuals so that early preventive and corrective measures can be undertaken.”
When such efforts are made, Dr. Buchman added, his own clinical experience parallels that of Dr. Lin’s. “It’s very common for us to see older patients with hearing loss experience some general slowing of their cognitive decline when we treat them for their condition,” he said.
Richard K. Gurgel, MD, an assistant professor of surgery in the division of otolaryngology-head and neck surgery at the University of Utah Health Care in Salt Lake City, sides with Dr. Lin when it comes to appreciating the link between hearing loss and cognitive decline in older patients. He and his colleagues presented a study, funded in part by a grant from the NIH, demonstrating the strength of that link at the annual meeting of the American Otological Society (held in conjunction with the Combined Sections Meeting) in Orlando in April.
The prospective, case-controlled cohort study included 4,463 men and women aged 65 years or older who did not have dementia at baseline, as determined by clinical assessment and expert consensus. Of those patients, 700 had hearing loss, based on observation of hearing difficulties or the use of hearing aids. In the hearing loss group, Dr. Gurgel and his colleagues reported, 16.3 percent developed dementia over the course of the study, compared with 12.1 percent of those without hearing loss. Mean time to dementia was 10.3 years in the hearing loss group vs. 11.9 years for patients with normal hearing.
The researchers controlled for important variables, including gender, education and the presence of apolipoprotein E alleles, which have been shown in some studies to be associated with sensorineural hearing loss (Neurobiol Aging. 2012;33:2230.e7-2230.e12). Once those factors were accounted for, the investigators found that hearing loss was an independent predictor of the development of dementia. When they analyzed the rate at which those cognitive declines occurred, they found that scores on the Modified Mini-Mental State (3MS) examination declined at a rate of 0.26 more points per year in hearing loss patients than in those with normal hearing.
These findings “suggest that hearing impairment may be a marker for central, cognitive dysfunction in adults aged 65 years and older,” Dr. Gurgel and his coinvestigators reported. But he was quick to point out the limits of the study. “There’s a difference between correlation and causation,” he told ENTtoday. “We don’t yet know whether the observed findings are due to a true neurobiological causative effect of hearing loss on dementia or whether the two simply correlate due to other yet-to-be-determined factors.”
Nevertheless, the evidence is strong, he said. “There have been enough large, epidemiologic studies of different populations that have shown an association between hearing loss and cognitive decline that I think an undeniable connection exists.”
And then there is the weight of clinical experience to consider. “I agree with Dr. Lin on this,” Dr. Gurgel said. “When elderly patients with or without cognitive decline can’t hear, they are effectively ‘cut off’ from their environment. They tend to become socially isolated and withdraw from otherwise enriching social interactions. By intervening with some form of aural rehabilitation, patients become much more engaged and their quality of life improves. I’ve seen this many times in my practice.”