Junior Surgery Lecture
Sensorineural Hearing Loss And Vertigo

Arun Gadre, M.D.

I. Sensorineural hearing loss

Sensorineural hearing loss (SNHL) implies dysfunction of the cochlea or auditory nerve. In most cases, the loss is irreversible, thus prevention and timely diagnosis and intervention is emphasized. Progressive loss implies an active disease while stable hearing is seen from a past insult. SNHL is more common than conductive loss and affects 10-20% of all people. The incidence increases with advancing age. There is an additive effect from different causes of hearing loss. Amplification (e.g. hearing aids) is the principal method of rehabilitation in this type of hearing loss. The various causes of SNHL will be grouped into congenital and acquired losses. The latter is much more prevalent.

A. Congenital

Nongenetic causes (perinatal infection, maternal illness) account for the majority of cases of congenital hearing loss. Hereditary hearing loss is typically through autosomal recessive transmission. Over 25 specific genes have been identified in familial hearing losses. This is an area of intensive research, and additional information on the genetics of congenital and acquired losses can be expected in the future.

The incidence of a significant SNHL at birth is ~1:1000 live births. However, an infant that possesses one or more of the following factors has a 1:25 chance of having a significant loss. high risk patients- Low birth wt (<1500gm), Hypoxia, Hyperbilirubinemia, maternal infection (esp rubella), neonatal meningitis, TORCH infection, ototoxic medications, Rh incompatibility, syndromic features, craniofacial anomaly

The diagnosis is made using objective measures of auditory acuity. Auditory brainstem evoked responses or otoacoustic emission testing is employed. The former test analyzes brainstem activity in response to an auditory stimulus, the latter is a test of cochlear hair cell function. Each test has a sensitivity and specificity of near 90%. Repeat testing must follow any abnormal test. The probability of multiple false positive responses is extremely small.

Once identified, early fitting of hearing aids is essential. Development of the auditory cortex occurs after birth. In the absence of auditory stimulation, this development will be delayed or prevented. Those infants with profound hearing loss may undergo cochlear implantation at age two years, though this limit may be lowered in the future.

B. Acquired

Each of the potential etiologies is listed in approximate order of prevalence.

1. Aging. All of us will experience some decline in auditory sensitivity with age. On average, age related decline in function is not detectable prior to age 65. On audiometric exam, a high frequency loss is present with poor word recognition. This is due to the combined effect of age related changes in cochlea (tones) and CNS (words).

2. Trauma. This is the most preventable type of hearing loss. Hearing loss may occur as the result of head injury or ear surgery, but the most significant factor is environmental noise. The effects of excessive noise are greatest in the frequencies of 4000-6000 Hz. This produces a notched audiogram with preservation of high frequency hearing above 6000 Hz. Thus the pattern is quite different from that seen due to aging. The effects of noise are cumulative over time, though the maximal rate of hearing loss is in the first five years of continual noise exposure. A sound intensity of at least 90dB is required to produce a noise-induced loss. Time and intensity of exposure predicts likeliness of injury. For a 90dB sound, a continuous exposure for eight hours can be damaging. The decibel scale is logarithmic, thus an increase of 5 dB decreases the allowed exposure time by one half. For very high intesity sounds (e.g. gunshots at close range) a very brief exposure can be significant. Note that OSHA guidelines require mandatory hearing protection for workers exposed to continuous noise of at least 85dB.

3. Infections. With only a few exceptions, otitis media is not a cause of SNHL. The principal infectious cause of SNHL is meningitis. The incidence of SNHL is approximately 15% for all cases of meningitis, but it does vary according to the organism. Rapid identification and antibiotic treatment are the mainstay of therapy for meningitis. Addition of steroid during the acute phase may limit the devastating effects of inflammation on the cochlea and cochlear nerve. Mumps and measles are occasionally associated with SNHL beginning within one to two weeks of the primary infection. Mumps is notable in that it may produce a unilateral SNHL. Syphilitic infection of the inner ear (otosyphilis) may produce SNHL and episodic vertigo. Treponemes may persist in the inner ear fluids much longer than in the blood. Antibiotic concentrations in the perilymph are notoriously poor. With prolonged antibiotic therapy vestibular symptoms may be controlled in most patients and some hearing improvement in possible.

4. Idiopathic. In the future, those hearing losses currently classified as idiopathic may be found to be hereditary or due to infectious cause.

5 .Neoplasm. The most common tumor producing SNHL is the acoustic neuroma (AN), or schwannoma of the eighth cranial nerve. AN is the most common tumor of the posterior fossa and accounts for 6-8% of all intracranial neoplasms. Age at diagnosis averages between 45 and 55 years. The tumors are bilateral in those with neurofibromatosis type 2. Presenting symptoms include unilateral high frequency SNHL and tinnitus. Even though the tumor grows on the vestibular division of the 8th nerve, dysequilibrium is usually absent. The diagnosis is made by MRI, which is nearly 100% sensitive in the detection of these tumors. Progressive tumor growth results in unilateral deafness and can cause significant brainstem compression if allowed to attain large size. Fortunately the tumor is rather slow growing. Surgery is the mainstay of treatment and can potentially save hearing if performed early in the course of the disease. Stereotactic radiation remains experimental, while observation is appropriate in selected cases.

6. Ototoxic medications. Aminoglycosides, cisplatin, and loop diuretics are the most important causes of iatrogenic hearing loss. Early symptoms usually include vestibular dysfunction and tinnitus as well as high frequency SNHL. Cessation of the medication is essential though hearing loss will progress due to slower elimination from the inner ear fluids. The patients at greatest risk are those that metabolize the drug inefficiently due to hepatic or renal failure. Genetic susceptibility to aminoglycoside ototoxicity has recently been discovered. Salicylates may produce reversible cochlear dysfunction. Tinnitus is the usual complaint, though hearing loss and vertigo may occur. Upon cessation of the medication, symptoms will abate in one to two weeks.

7.Vascular

8.Autoimmune

II. Vertigo

Definition - an illusion of movement of the environment when patient is stationary. The sensation of vertigo is highly specific for a disorder of the inner ear, while other vague sensations of dizziness are less likely to be of labyrinthine origin. The history is crucial in allowing a proper diagnosis. Often a significant amount of time is necessary to understand the patient's sensation of "dizziness". Most people have experienced the sensation of vertigo; common inciting events include carnival rides, the playground merry-go-round, alcohol intoxication, or sea-sickness.

The three most common causes of vertigo are presented. Combined, these three diagnoses would account for approximately 66% of all patients presenting with vertigo to an ENT specialist. Their incidence in a primary care practice is probably even greater.

A. Vestibular Neuritis aka Labyrinthitis

Vestibular neuritis(VN) implies an inflammatory process involving the vestibular division of the eighth cranial nerve or balance portion of the inner ear (vestibule and semicircular canals). When the cochlea becomes involved, as evidenced by accompanying hearing loss, the term labyrinthitis is used. The precise etiology is uncertain, though it is widely believed to be the result of viral infection or reactivation.

The patient presents with the acute onset of severe vertigo, lasting several hours to days. Severe nausea and vomiting are often present, occasionally leading to dehydration. The symptoms typically occur in conjunction with, or soon after, an upper respiratory infection. The patient is often unable to come to the physician's office due to the severity of symptoms and may present to the ER.

In the acute phase, spontaneous nystagmus is present with the fast phase directed away from the affected ear. The nystagmus is rapidly suppressed in younger individuals, but may persist for several days in the elderly. Head shaking may elicit the nystagmus in some. Hearing loss is not present in VN, but is present in labyrinthitis. There are no other consistent findings on the head and neck exam.

Treatment for nausea is essential in the acute phase. Short term use of vestibular suppressants(e.g. meclizine) and antiemetics (e.g. promethazine) is valuable to allow the patient to resume daily acitivities. However, their use should be limited to one week at most. Longer use will impair the process of central compensation for the resulting vestibular deficit. Following an injury/infection of the inner ear, some permanent damage to the sensory epithelium occurs, changing the sensitivity of the inner ear to motion. The brain must adjust to the altered sensory information coming from the affected inner ear and rectify the imbalance in sensory inputs from both sides. This process of recallibration is remarkably efficient as long as it is allowed to proceed. Vestibular exercises also promote recovery by producing motion stimulation at greater speeds than typically encountered in daily acitivities.

B. Benign Paroxysmal Positional Vertigo

BPPV is the most common cause of vertigo. It is thought that BPPV occurs secondary to accumulation of debris within the posterior semicircular canal (PSCC). The source of the debris may be otoconia from a degenerating utricular macula. Otoconia have a density approximately 2.5 times greater than endolymph, thus particles in suspension would tend to precipitate in the PSCC, the most dependent portion of the inner ear. Any head movement in the plane of the PSCC sets the particles in motion. This alters the sensitivity of the PSCC ampulla and the patient experiences vertigo. Vestibular neuritis, head trauma, and aging may predispose a patient to development of BPPV.

The presenting symptom is episodic vertigo, lasting several seconds to one minute, and precipitated by specific head movements. Episodes may occur multiple times each day, but the patient is well between episodes.

The diagnosis is confirmed on physical exam. A characteristic rotary nystagmus occurs when placing the patient in the Hallpike position. The nystagmus displays some latency in onset, and fatigues with repeat testing. No hearing loss is present.

Treatment- Several techniques have been devised to remove sediment from the PSCC through non-invasive exercises. Each is based on the assumption that the debris can be moved to an asymptomatic region of the inner ear (where it is not in contact with one of the sensory structures). The utility of these approaches is confirmed by many authors, who report improvement of symptoms in nearly ninety percent of patients. There is no role for vestibular suppressants in this disorder. The duration of symptoms is much shorter than the onset of action of the medication and these medications will not prevent the next episode of BPPV.

C. Meniere's disease

Meniere's disease is a clinical diagnosis based on the presence of characteristic history and audiometric findings. It is believed that the symptoms result from excessive endolymph accumulation due to either altered synthesis or resorption. The etiology is unknown. The disease is bilateral in at least one third of cases.

The patient has recurrent vertigo, with each episode lasting a minimum of 20minutes. Aural pressure, tinnitus, and a low frequency fluctuating hearing loss are also variably present and worsen in conjunction with the vertiginous episodes. Serial audiometric exams display a low frequency SNHL, which improves during asymptomatic intervals. Over the long term, the hearing loss progresses despite therapy.

Favorable control of vertigo is often seen by limiting salt intake and prescribing a diuretic(e.g. hydrochlorothiazide). Stress reduction, reduction of caffiene and alcohol intake, and smoking cessation are also advocated. Unfortunately, the hearing loss and tinnitus are mostly resistant to therapy. When this intervention is not successful, destruction of the involved labyrinth can eliminate vertigo. This is accomplished by chemical or surgical ablation or deafferentation (vestibular nerve section). Central compensation occurs after surgical intervention, usually allowing the patient to continue with regular activities without the threat of vertigo.

D. Non-vestibular dizziness

When the patient reports vague dizziness that is not vertigo, it is more likely that the symptom is not due to inner ear dysfunction. The complaints may include syncope, lightheadedness, imbalance, or ataxia. A thorough search for associated cardiovascular, neurological, or psychiatric symptoms is important in obtaining the correct diagnosis. The differential diagnosis includes Orthostasis (dehydration), Arrhythmia, Carotid stenosis, Vertebrobasilar insufficiency, Seizure disorder, Brainstem anomaly, Anemia, Psychophysiologic (Hyperventilation, anxiety), Degenerative Neurologic disease(MS, Parkinson's), Hydrocephalus, Migraine and Multisensory Dysequilibrium (due to aging).