Understanding Hearing Loss and Tinnitus
Hearing loss can be conductive, sensorineural, or mixed, which is a combination of conductive and sensorineural. The type of hearing loss is correlated with the anatomic part of the ear affected (outer, middle, or inner ear). Generally, damage to the outer and middle ear causes conductive hearing loss, whereas inner ear damage results in sensorineural hearing loss (Medwetsky 2007).
Conductive Hearing Loss
Outer and middle ear conductive hearing loss could be caused by infections, trauma, congenital malformations or tumors in the outer ear. Otitis media, a common childhood disease that can also affect adults, is one of the most common types of ear infections to cause hearing loss; similarly, viral infections of the upper respiratory tract can affect the ear and cause temporary hearing loss. Trauma to the tympanic membrane, one of the middle ear structures that help translate sound waves into interpretable neurologic signals, can also result in conductive hearing loss. The tympanic membrane can become damaged by direct trauma, which can be caused by a foreign body such as a cotton swab (e.g., Q-tip®), infection, and sudden changes in air pressure (middle ear barotrauma) (Weber 2012).
Sensorineural Hearing Loss
Damage to the inner ear is usually responsible for hearing loss that progresses over time. Presbycusis, or age-related deterioration of hearing ability, is marked by the gradual loss of high frequency hearing on both sides in elderly individuals (Huang 2010). Presbycusis is also associated with tinnitus (i.e., ringing in the ears). Excessive noise can also cause sensorineural hearing loss that can gradually increase over time. Loud noise damages the delicate structures in the ear both due to trauma and accumulation of free radicals & excess glutamate, as well as altering intracellular magnesium and calcium levels (Prasher 1998). Infections and a condition called Meniere’s diseasecan also lead to inner ear damage and sensorineural hearing loss (Weber 2012; Mayo Clinic 2010).
Closely linked to hearing loss is a condition known as tinnitus, characterized by a persistent ringing sensation in the ears. Although tinnitus can be triggered by a variety of causes, the majority of cases are associated with hearing loss (Roberts 2010). Researchers are still working to understand the process behind tinnitus. One popular hypothesis is when the hair cells (specialized nerve cells that help translate sound waves into interpretable signals for the brain, not to be confused with hair follicles) in the cochlea are damaged, some of the associated neurons partially lose the inhibitory regulation that keeps them from firing when no sound is present. As a result, these neurons send signals that the brain perceives as persistent noise. Supporting this hypothesis is that many people who suffer from tinnitus perceive the “ringing” in their ears to be of the same or similar frequency to their hearing deficits. Consequently, similar processes that lead to hearing loss may also lead to tinnitus; thus, interventions that prevent hearing loss may also prevent tinnitus (Roberts 2010).