Introduction ------------ Presbycusis refers to bilateral age-related hearing loss. In literal terms, presbycusis means "old hearing" or "elder hearing."[\[1\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) It becomes noticeable around age 60 and progresses slowly; however, there is evidence that certain stressors can speed the rate of deterioration. The diagnosis can be confirmed with audiometry.[\[2\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) The hallmark of presbycusis is the impaired ability to understand high-frequency components of speech (voiceless consonants, such as p, k, f, s, and ch).[\[3\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) There is no cure; however, hearing aids that amplify sounds can be used to mitigate symptoms. Anatomically, presbycusis involves multiple components of the auditory system. It is primarily due to age-related changes in hair cells, the stria vascularis, and afferent spiral ganglion neurons.[\[4\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) During the normal hearing, sound, in the form of air vibration, is captured by the funnel-shaped external ear and is directed to the tympanic membrane. This causes the tympanic membrane to vibrate at a specific frequency and amplitude. This movement is amplified by three small bones in the middle ear: the malleus, incus, and stapes. From there, the signal proceeds as vibrations that are transmitted through the fluid within the inner ear to the cochlea. In the cochlea, receptors known as hair cells transform the information encoded in the vibrations into a neurologic signal which travels to the auditory cortex via the cochlear nerve.[\[5\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) Etiology -------- Presbycusis is multifactorial in origin. In addition to age-related degeneration leading to physiologic and anatomic changes, other contributing factors include genetic factors, hormones, exposure to loud noises or ototoxic agents, history of ear infection, and the presence of certain systemic diseases.[\[6\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[7\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) **Age-Related Factors** Presbycusis can be broken down further with regards to which structures and functions are primarily affected. Some argue that there is little clinical utility in subdividing presbycusis as there is no significant change in approach or treatment, and oftentimes mixed pathology is present.[\[6\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[8\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[9\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) Presently, there are thought to be six categories of presbycusis: sensory, neural, strial, mechanical, mixed, and indeterminate.[\[4\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[10\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) * Sensory presbycusis: loss of receptor hair cells at the basal aspect of the cochlea resulting in characteristic high-frequency hearing loss.[\[6\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) * Neural presbycusis: loss of cochlear nerve fibers as well as the loss of spiral ganglion neurons. * Strial presbycusis: degeneration of stria vascularis cells. These cells are essential for maintaining the appropriate ion composition of endolymph to generate the endocochlear potential for signal transduction.[\[11\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) Sometimes referred to as metabolic presbycusis. * Mechanical presbycusis (cochlear conductive): due to physical changes of the cochlear duct. This is accompanied by a specific audiogram pattern.[\[4\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) * Mixed presbycusis: characterized by pathologic changes in more than one of the above structures. * Indeterminate presbycusis: cases in which changes to the above structures are not significant.[\[4\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) **Genetic Factors** Genetic factors, specifically, differences in mitochondrial DNA expression genes related to oxidative stress, have been found in patients with presbycusis when compared to controls.[\[12\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[13\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[14\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) **Ototoxic Factors** There are multiple medications associated with ototoxicity, including salicylates, loop diuretics, aminoglycoside, and certain chemotherapeutic agents.[\[15\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[16\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[17\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) Additionally, some work and environmental-related exposures to chemicals such as toluene, styrene, lead, carbon monoxide, mercury, and other toxins have been shown to cause ototoxicity.[\[18\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) Minimizing exposure to these agents can help to prevent age-related hearing loss.[\[19\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) **Noise Exposure Factors** Some long-term studies have shown that individuals who have sustained noise-induced cochlear damage in their youth go on to develop more severe presbycusis**.** Anatomically, noise exposure may lead to damage and subsequent loss of spiral ganglion neurons.[\[14\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[20\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) **Hormonal Factors** Glucocorticoids, sex hormones, and glutamate signaling are thought to play a role in presbycusis.[\[14\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) Prolonged corticosterone levels and loss of nuclear factor kappa B have been associated with increased spiral ganglion neuron loss.[\[21\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) [\[22\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) The use of progestin and combination hormone replacement therapy in postmenopausal is associated with a more frequent incidence of hearing loss.[\[23\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) Pathophysiology --------------- Presbycusis is thought to be multifactorial in origin, and some components are not fully understood. Both intrinsic factors, such as genetics, as well as external factors (noise exposure, smoking, medications, and certain co-morbidities), are involved.[\[3\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) It is primarily due to age-related changes in hair cells, the stria vascularis, and afferent spiral ganglion neurons.[\[4\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#) Presbycusis is a type of sensorineural hearing loss with the involvement of the inner ear or neurologic pathways that form connections to the auditory cortex.[\[2\]](https://www.ncbi.nlm.nih.gov/books/NBK559220/?utm_source=chatgpt.com#)