Clinical Pearls & Morning Reports
Published December 20, 2017
In the United States, the prevalence of hearing loss doubles with every 10-year increase in age. Read the latest Review Article.
Q: What are some of the causes of hearing loss in adults?
A: The leading cause of adult-onset hearing loss is the effects of aging on the auditory system. Hearing loss in older persons is caused not only by the degenerative effects of aging on the cochlea but also by the accumulated effects of exposure to noise and ototoxic drugs. Approximately 104 million people in the United States are exposed to levels of noise that can cause hearing loss, and 1 in 4 adults in the United States has measurable hearing loss caused by exposure to harmful noise. Noise damages the sensory hair cells of the inner ear through the direct mechanical stress of intense sound pressure and by activation of stress-induced molecular pathways, including generation of reactive oxygen species and calcium overload. Various chemicals and drugs adversely affect the auditory system; the main ones in clinical use are aminoglycoside antibiotics and cisplatin, both of which are toxic to sensory hair cells. The prevalence of sudden, idiopathic hearing loss is 5 to 20 cases per 100,000 population, with approximately 4000 new cases per year in the United States. The cause of sudden hearing loss is not known but is presumed to be viral, vascular, or autoimmune.
Q: In cases of sensorineural hearing loss, is it possible to determine whether the abnormality is located in the sensory or the neural portion of the peripheral auditory system?
A: The broad term “sensorineural hearing loss” has been used by clinicians because, until recently, diagnostic tests could not determine whether a lesion was in the sensory or the neural portion of the peripheral auditory system. This distinction is now made by measuring otoacoustic emissions, performed by simultaneously presenting tones of different frequencies and sound pressures to the external canal and detecting sound emissions from the cochlea itself; the results reflect the functioning of outer hair cells of the cochlea. Auditory brain-stem responses also test the neural component of audition by recording synchronous neural activity of the auditory nerve and auditory brain-stem nuclei.
A: The frequency of use of hearing aids by adults with hearing loss is low. The United States is one of the few developed countries that does not offer government assistance for the purchase of hearing devices. In October 2015, the President’s Council of Advisors on Science and Technology recommended that the FDA create a new regulatory class for hearing aids that can be sold over the counter for persons with mild or moderate hearing loss. This recommendation was endorsed by the National Academies of Sciences, Engineering, and Medicine in their report titled “Hearing Health Care for Adults: Priorities for Improving Access and Affordability,” released in June 2016. They recommended that the FDA create a category of over-the-counter, wearable hearing devices that would be regulated to meet specific safety and quality standards and labeling specifications; the new FDA classification would preempt current state laws and regulations in order not to limit access to affordable hearing aids. Legislation has recently been signed into law that requires the FDA to create and regulate a category of over-the-counter hearing-aids for adults who have mild to moderate hearing loss.
A: A review of novel therapies included 22 active clinical drug trials registered on the National Institutes of Health ClinicalTrials.gov website. Most of these proposed treatments address cell-death pathways and mitigate the effects of oxidative stressors on inner-ear hair cells. Commercially sponsored trials of antibiotic and chemotherapeutic medications for the treatment or prevention of ototoxicity are planned or are under way. One study uses a viral vector to deliver gene therapy to the inner ear. Preclinical studies in animal models suggest that viral-vector gene therapy may be valuable in treating monogenetic hereditary hearing loss.