The classic presentations of various causes of hearing loss are given here, but not all of the associated symptoms or additional symptoms may be present with any given condition. Sensorineural hearing loss (SNHL) constitutes 92% of hearing loss in older adults, with the remainder being conductive or mixed (both sensorineural and conductive components). In the vast majority of cases, hearing loss in older adults is multifactorial, and many etiologies concurrently lead to hearing loss over time. Of note, subjective tinnitus, which is a centrally mediated process, can accompany any type of hearing loss as a result of the alteration of auditory input to the auditory cortex in the temporal lobe.
Sensorineural Hearing Loss (Inner Ear Disease)
An audiogram typical of presbycusis (age-related hearing loss) shows a down-sloping SNHL, in which the higher frequencies (toward 8 kHz) are more severely affected than lower frequencies (toward 250 Hz) (Figure 62–1). Patients often are unaware of their degree of hearing impairment because of its gradual progression over years. The patient’s friends and family members are often the first to notice and may prompt the patient to seek evaluation and treatment. In some patients, hearing loss may be accelerated due to hereditary factors.
Audiogram of presbycusis. An audiogram demonstrating moderate SNHL typically seen in presbycusis (age-related hearing loss). Note that the higher frequencies are more affected than the lower frequencies. Physician’s Choice Hearing and Dizziness Center. (Available at http://hearinganddizziness.com/. Accessed October 8, 2012. Used with permission.)
Noise-induced hearing loss can result from prolonged exposure to noise, in which case the hearing loss would be permanent and occur gradually over months to years, or from brief exposure to intense noise, in which case the hearing loss may be sudden and may be temporary or permanent. The audiogram for these patients typically shows a dip on the audiogram at 3–6 kHz and may be unilateral or bilateral depending upon the nature of the injury. Noise-induced hearing loss is preventable with avoidance and use of ear plugs and other hearing protective devices.
Various infections can cause hearing loss. Viral, bacterial, or fungal labyrinthitis can cause hearing loss that is typically unilateral with associated tinnitus and vertigo. Meningitis, particularly bacterial, can cause partial to complete hearing loss through direct damage to the cochlea. Syphilis and lyme disease are known to cause sudden SNHL. Herpes zoster oticus, known as Ramsay Hunt syndrome, because of reactivation of the zoster virus in the geniculate ganglion, begins as painful vesicles in and around the external ear followed by any or all of the following: sudden unilateral hearing loss that may be temporary or permanent, tinnitus, nystagmus, disequilibrium or vertigo, and/or facial weakness that may be temporary or permanent. The diagnosis can be made by isolating the virus from vesicular fluid.
Autoimmune inner ear disease—
A number of autoimmune diseases are associated with hearing loss that is typically progressive and bilateral in nature, including, but not limited to, systemic lupus erythematosus, polyarteritis nodosum, inflammatory bowel disease, Crohn disease, ulcerative colitis, and granulomatosis with polyangiitis. There are also some patients who experience hearing loss and/or dizziness outside of a known disease process who respond to immunosuppressive therapy. The hearing loss in these conditions is thought to be caused by direct damage to the cochlear and vestibular organs through antibody-mediated attack by the host immune system.
Systemic and vascular disease—
Multiple systemic diseases can result in hearing loss, primarily through their effects on the vasculature of the cochlea. The blood supply to the cochlea is composed of terminal branches of the intracranial circulation and is subject to vascular insult with subsequent ischemia or even infarction. Diabetes mellitus, small vessel vasculitides, and microthrombotic or embolic events may lead to sudden or gradual hearing loss. Furthermore, hearing loss, vertigo, and/or nystagmus can be some of the presenting symptoms of a central ischemic or hemorrhagic stroke.
Signs and symptoms that a patient may be experiencing ototoxic effects include the development of new tinnitus, vertigo or disequilibrium, and difficulty hearing. If these symptoms develop, the patient should be evaluated and the drug should be stopped immediately if possible. Table 62–3 lists some of the most common ototoxic medications.
Table 62–3.Common ototoxic medications.
Acoustic neuroma (Vestibular schwannoma)—
These small tumors of cranial nerve VIII typically present with unilateral, slowly progressive, high-frequency SNHL, but may present as sudden SNHL in up to 25% of patients. Commonly associated symptoms included tinnitus in 70% of patients, disequilibrium or vertigo in 50% of patients, cranial nerve (CN) V dysfunction (often subclinical) in 50% of patients, and/or facial weakness or asymmetry in 2% of patients. MRI with gadolinium is the study of choice for diagnosis.
Also known as endolymphatic hydrops, this condition is characterized by episodic rotational vertigo that is typically debilitating and lasts from 20 minutes to 24 hours, but typically 1–2 hours. It is associated with fluctuating low frequency hearing loss, aural fullness, and tinnitus. The symptoms almost always begin unilaterally, but the contralateral ear may become involved in up to 50% of patients over time. The natural history is a relapsing and remitting course with the disease often “burning out” over time. Recurrent attacks can lead to a permanent SNHL.
Temporal bone fractures from falls, motor vehicle accidents, assault, or other blunt trauma can cause SNHL if the inner ear is involved. Additionally, patients can suffer facial nerve paresis that can be delayed or immediate and injury to surrounding structures. A temporal bone protocol CT scan without IV contrast will make the diagnosis in these patients.
Sudden sensorineural hearing loss—
Sudden SNHL is a sudden decrease in hearing thresholds of 30 dB or greater at 3 contiguous audiometric frequencies occurring over 72 hours or less and is an otologic emergency that occurs in an estimated 5–20 per 100,000 people per year. The primary goal in managing these patients is the prevention of permanent SNHL through prompt referral to an otolaryngologist for confirmation and treatment with steroids within 24–48 hours. Distinguishing between sudden SNHL (requiring immediate referral) and an acute conductive loss from an ear infection or middle ear effusion (treated with simple antibiotics or a nasal steroid spray and not requiring urgent referral) can be made using the tuning fork tests described above.
A history of radiation to the head or neck, for either a neoplastic process or environmental exposure, can lead to SNHL by direct damage to the inner ear and auditory nerve.
Conductive Hearing Loss (Middle or External Ear Disease)
Conductive hearing losses are far less common than SNHLs in older adults and can often be diagnosed in the clinic by otoscopic examination or through tuning fork testing. Common causes include EAC obstruction (eg, cerumen), TM perforations, middle-ear effusions, and ossicular chain pathology. Middle-ear effusions caused by eustachian tube dysfunction can often be treated with intranasal steroids and oral antibiotics (if there is a concern for acute otitis media) and followed conservatively for 2 months. Failure of resolution or concern for any other etiology for a conductive hearing loss warrants referral to an otolaryngologist.