Men with sudden sensorineural hearing loss are more likely to have previously diagnosed obstructive sleep apnea than those without the hearing loss.
A study by Jau-Jiuan Sheu, MD, an associate professor of neurology at Taipei Medical Hospital in Taiwan, and colleagues, matched 15,960 control patients with 3,192 patients with newly diagnosed sudden sensorineural hearing loss. (Arch Otol Head Neck Surg 2012;138:55.)
Patients with that type of hearing loss also had higher rates of obesity, hyperlipidemia (18.2% vs. 13.7%); diabetes (16.3% vs. 11.4%); hypertension (32.0% vs. 25.7%); and coronary heart disease (14.2% vs. 10.9%). A total of 240 of the 19,152 patients were diagnosed with obstructive sleep apnea before the index date (1.2%), with 55 (1.7% of the total) in the sudden sensorineural hearing loss group and 185 (1.2% of the total) in the control group.
This population-based, case-control study didn't prove causality, even though a higher proportion of obstructive sleep apnea was found among patients with this type of hearing loss compared with controls. The researchers said, however, that it does present a situation that is highly plausible.
“There are a number of different reasons why these results were demonstrated in the study,” said Steven Park, MD, a surgeon at Montefiore Medical Center in Bronx, NY. “Sleep apnea causes major inflammation in the bloodstream and brain, and also promotes vascular complications. People with sleep apnea also have thicker blood, so blood [is] sludgy and clots.
“We know that blood vessels that go to the inner ear are of a tenuous blood supply [with] one major artery that fans out into all branches of the cochlea. You can imagine if you have all these factors combined, you will be prone to mini-stroke in one part of your cochlea. Things that can bring it on are infection, dehydration, increased weight, and other inflammatory conditions,” he said.
This result, though, was present only in men with sudden sensorineural hearing loss. No statistical difference was found between women with the hearing loss and controls for prior obstructive sleep apnea, an outcome that may be gender biased. “I think there may be a bias that women are less exposed to obstructive sleep apnea, but [it] is also not investigated as much in women,” said Seva Polotsky, MD, an associate professor of medicine at Johns Hopkins University in Baltimore. “The second possibility is that hearing loss may be associated with more severe apnea, so maybe more mild cases don't lead to these complications.”
The researchers said the relationship between obstructive sleep apnea and sudden sensorineural hearing loss may be associated with a number of cardiovascular and metabolic consequences. “A possible explanation for the association … is that obstructive sleep apnea indirectly contributes to the development of sudden sensorineural hearing loss via the effects of cardiovascular disease and cardiovascular risk factors,” the authors of the Taiwanese study wrote.
Dr. Polotsky said sleep apnea leads to dyslipidemia and increased cholesterol levels, and directly affects vascular walls because of oxidative stress or inflammation. “It's well proven that sleep apnea increases blood pressure. A combination of these factors results in an increase of cardiovascular disease, which may result in cerebrovascular insufficiency that may lead to hearing loss,” he said.
The study, though, depicts only a link that doctors like Dr. Park have seen in patients, and more prospective and clinical studies are needed. “I would say that this study should lead to two types of future studies,” Dr. Polotsky said. “The first study should be a large prospective study, with this existent cohort being used and those who already have hearing loss excluded. They should be followed over a number of years and observed to see whether development of hearing loss is associated with high incidents of sleep apnea.
“For causality, you need a treatment trial. You have to enroll patients with hearing loss and treat their sleep apnea and see if they get better. But the one caveat is that hearing loss may be irreversible, so that may negate the study,” Dr. Polotsky said.
Dr. Park said “a very high number of patients” will be required to complete a treatment trial.