NEURO-OTOLOGY (Continued)

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Because ongoing or episodic conditions accompanied by vertigo, unsteadiness, or presyncope are produced by multiple and often subtle causes, it is not surprising that a significant number of patients cannot be readily diagnosed. A major differential diagnostic classification would include broad categories such as (1) peripheral vestibulopathy, (2) central neurological disorders, and (3) systemic or medical conditions. There is some ambiguity in the use of the term central, which has been used by otolaryngologists to include causes that are central or proximal to the vestibular end organ and therefore include the vestibular portion of the eight nerve. Neurologists, however, consider conditions that affect the vestibular nerve, such as tumors, as peripheral in location because they are on a cranial nerve and are extra-axial. Because masses or neoplasms can enlarge to involve other structures in the cerebellopontine angle, particularly the brainstem, conditions that affect the VIII nerve are discussed for convenience in the central category.

PERIPHERAL CAUSES {Back to Outline}

Peripheral causes result from dysfunction of vestibular end organs (semicircular canals, utricle, and saccule) (Table 2):

Peripheral Vestibulopathy{Back to Outline}

Peripheral vestibulopathy, encompasses terms such as vestibular neuronitis, labyrinthitis and viral neurolabyrinthitis. Such terms imply an inflammatory mechanism, which is unproved. Vestibular neuronitis, strictly speaking, is characterized by single or recurrent sudden episodes of true vertigo lasting from hours to days and often associated initially with vomiting. When the condition is associated with hearing loss, the entire labyrinth is assumed to be involved, and the term labyrinthitis is used. Despite this technical distinction, many neuro-otologists, otologists, and neurologists use the terms vestibular neuronitis and labyrinthitis interchangeably, whether or not auditory symptoms are present. In such patients the vertiginous sensation may be provoked by head movement, but not necessarily by a particular head position. Whether isolated viral involvement of the vestibular nerves is a cause of acute or episodic vertigo is controversial. Many prefer the term acute or recurrent peripheral vestibulopathy. In the acute phase, many patients present with sudden severe vertigo, nausea, and vomiting without any hearing disturbance or facial weakness. The acute symptoms usually resolve in a few days to a week, but may recur in weeks or months. If true vertigo is part of the symptom complex, the condition is most likely to be associated with some disorder of the peripheral end organ. However, patients with either acute peripheral vestibulopathy or, more commonly, recurrent attacks may experience only a sensation of lightheadedness or floating, or a feeling of "walking on tennis balls." Even if the patient has had hundreds of episodes, it is important to determine whether any of them were associated with spinning vertigo. Over time, the nature of the patient's symptom complex may change, even with peripheral vestibulopathy, from vertiginous sensations to those of pure unsteadiness or disequilibration.

Epidemic and seasonal outbreaks of acute vertigo have suggested an infectious origin due to viral disease, but this largely remains unproved. Viral labyrinthitis can also be part of a systemic viral infection such as mumps, measles, infectious mononucleosis, or upper respiratory tract viral infections. Isolated viral infections of the labyrinth are also believed to cause the sudden onset of hearing loss and/or vertigo in both children and adults. Otitic Herpes zoster is an infection characterized by pain in the ear, followed in 1 to 10 days by a vesicular eruption in the external ear. When the VIII and VII nerves are affected, there is a combination of facial weakness, hearing loss, and vertigo known as the Ramsay Hunt syndrome. Whenever vertigo is associated with severe ear pain or facial pain, one must consider this possibility. A dysesthetic area of skin may precede, by many days, the appearance of the skin eruption.

Benign Positional Vertigo{Back to Outline}

Benign positional vertigo refers to a symptom complex classically described as indicative of benign peripheral (end organ) disease. These symptoms, differentiated from central neurological symptoms, are outlined in Table 3.

The signs and symptoms of benign positional vertigo are transient and rarely last longer than 40 seconds. They frequently occur when a certain position is assumed, such as lying down or turning in bed. Other causes of vertigo are also intensified by position change. Depending on whether the symptom (vertigo) or sign (nystagmus) is being emphasized, this condition is termed paroxysmal postional vertigo (BPPV) or benign paroxysmal positional nystagmus (BPPN). In a major review of 240 cases, Baloh and associates described the clinical and eye movement recording features in patients with BPPV. In each case, after a rapid position change from the sitting to head-hanging position, a stereotyped torsional paroxysmal nystagmus was observed. The time to the onset of the nystagmus, the latency, was from 0 to 40 seconds, with an average of approximately 8 seconds. The initial phase of the nystagmus was rotary and upward, with the upper pole of the eye beating toward the ground on visual inspection. From the examiner's observation the nystagmus should appear counterclockwise, with the left ear down. The average age of onset was 54 years and the most common identifiable causes were head trauma (17%) and viral neurolabyrinthitis (15%).

Troost and Patton (1992) described historical factors which should lead to the consideration of BPPV: (1) symptoms associated with certain head positions, (2) rotational vertigo, episodic in nature, (3) antecedent episode of severe rotary vertigo with or without nausea and vomiting associated with upper respiratory infection that suggests prior viral neurolabyrinthitis, (4) history of head trauma before attacks of vertigo, (5) most severe symptomatology early in the day with lessening symptoms as the day progresses, and (6) relative absence of spontaneous symptoms without head movement or positional change. Physical examination findings include (1) vertical-rotary benign positional paroxysmal nystagmus (BPPN) produced by provocative maneuvers. (Figure 3):

Figure 3. Provocative maneuvers for positional vertigo and nystagmus. The patient is abruptly moved from a seated position to one with the head hanging 45 degrees below the horizontal and rotated 45 degrees to one side. He or she is then observed for positional nystagmus. The maneuvers are repeated with the head straight back and turned to the other side.

(2) latency to onset of symptoms once precipitating head position is achieved, (3) short-duration nystagmus (3 to 30 seconds), and (4) adaptation of nystagmus and symptoms--ie, disappeance with repeated maneuvers. An additional feature of the physical examination is that BPPN is not a constant feature, being present on some examinations but absent at other times. The finding of the typical nystagmus upon assumption of certain head postures is considered the single most important physical finding in making the diagnosis of BPPV. The nystagmus or ocular oscillation is depicted in Figure 4:

Figure 4 In benign paroxysmal positional nystagmus (BPPN), the nystagmus fast phase is horizontal-rotary directed toward the undermost ear when gaze is directed toward the undermost ear (upper panel). The nystagmus fast phase is upward toward the forehead when gaze is directed to the uppermost ear (middle panel). With the eyes in the central orbital position, the nystagmus fast phase is vertical upward and rotary toward the down ear (bottom panel).

Mechanism of BPPV{Back to Outline}

It is believed that the short, usually intense, episodes of vertigo and nystagmus are caused by two mechanisms:
(1) Cupulolithiasis: a dislocation of the calcium carbonate crystals which rest on the hair cells of the saccule and utricle of the inner ear which make them susceptible to the pull of gravity. These "ear stones" or otoliths become dislodged due to trauma, prior infection (neurolabyrinthitis or "vestibular neuronitis"), as a normal part of the aging process in 80% of people living between 60 and 80 and just by chance. The otoliths usually settle on the active part of the posterior semicircular canal and convert the receptor from one sensistive to accelleration to one sensitive to position and changing of position. The concept of cuplolithiasis is bolstered by some histopathology. It is depicted in the following diagram:

The otolith (red, in the insert) has located to the top of a hair cell in the cupula. Exercise therapy is used to move it and eliminate the condition (see treatment section).
(2) Canalithias: Otoliths or "dense bodies" become located in the canal itself near the cupula, again in a position to cause symptoms with change in head position. Canalithiasis is depicted in the following diagram:

The dense bodies (violet) or otoliths (blue squares [depending on your viewer]) are lodged near the cupula. A series of head position changes can move the material to a non-sensitive portion of the inner ear (see treatment section).

Post-Traumatic Vertigo{Back to Outline}

Post-traumatic vertigo immediately follows head trauma in most cases implying end organ damage in the absence of other central nervous system signs. The interval between injury and onset of symptoms can, however, be days or even weeks. The mechanism for the delay of symptoms is uncertain but includes hemorrhage into the labyrinth, with later development of serous labyrinthitis. Another mechanism for delayed post-traumatic positional vertigo is cupulolithiasis in which the calcareous deposits (otoconia) of a damaged organ of the labyrinth are displaced to a sensitive region of the posterior canal making it more susceptible to stimulation in certain head positions. In posttraumatic vertigo, the symptoms may be those of general peripheral vestibulopathy or benign positional vertigo. Generally, the prognosis is good with symptoms gradually resolving within weeks to months. As pointed out by Baloh and colleagues, disabling persistent positional vertigo unresponsive to medical therapy, occurs more commonly than was previously recognized. The vast majority of patients respond to exercise therapy, as described below, and rarely need selective section of the nerve to the posterior semicircular canal.

Drug Toxicity{Back to Outline}

Patients with dizziness produced by vestibulotoxic drugs are presumed or documented to have persistent injury to the peripheral end organ. Among the agents causing such end organ injury are the aminoglycosides. Streptomycin and gentamicin are most detrimental to the vestibular end organ; kanamycin, tobramycin, and neomycin cause more damage to the auditory end organ. Patients usually report progressive unsteadiness, particularly when visual input is diminished, as happens at night or in a darkened room. Vestibular testing documents a progressive bilateral loss of vestibular function. The aminoglycosides are concentrated in the endolymph and perilymph, thus the hair cells are exposed to high concentrations of the drugs. Extreme caution should be used in patients with renal disease because most of these agents are primarily eliminated by the kidney. This type of end organ toxicity should be contrasted with that produced by the large group of drugs with widespread reversible central and peripheral nervous system effects such as anticonvulsants and hypnotics (See section on Systemic Causes of Dizziness). The non-toxic drugs listed cause transient disequilibration which subsides with cessation of the medication.
A brand NEW chapter has been posted (current date 1-23-98) concentrating entirely on toxicity to the hearing and balance system: Drug Induced Vestibulocochlear Toxicity

Meniere's Syndrome{Back to Outline}

Meniere's syndrome is characterized by attacks of severe vertigo, tinnitus, fluctuating hearing loss and ill-described aural sensations of fullness with spontaneous recovery in hours to days. Initially, the patient develops a sensation of fullness and pressure along with decreased hearing and tinnitus in a single ear. This is followed by severe vertigo, which reaches peak intensity within minutes and slowly subsides over hours. There is persistent sense of disequilibration for days after an acute episode. Occasionally, sufferers from Meniere's syndrome experience such severe attacks that they suddenly fall to the ground. Consciousness is not lost in such episodes, although awareness of surroundings may be altered by the intensity of the accompanying sensation and nausea which has been called Tumarkin's crisis. The most consistent pathological finding in Meniere's syndrome is an increase in the volume of the endolymphatic fluid and distention of the canals, hence the term endolymphatic hydrops. Although some specific causes such as bacterial, viral, and syphilitic infections may lead to the same pathological changes and symptoms, the majority of cases are idiopathic. Meniere's disease usually develops between the ages of thirty and fifty and is slightly more common in women than in men. The prognosis is for progressive reduction in hearing along with increasing frequency of attacks. Some patients stabilize with no subsequent attacks of severe vertigo, but they are left with residual hearing loss. Fifty percent of Meniere's patients become bilateral. The hearing loss often progresses to a moderate degree of deficit and then stabilizes.

Other Peripheral Vestibular Conditions{Back to Outline}

Many other disorders affect the peripheral labyrinth, including acute otitis media, chronic ear infection, hereditary degenerative disorders of the end organ, and local tumors. Conditions such as a vertebrobasilar transient ischemic attack (TIA) or focal ischemic stroke of the end organ, particularly in an elderly patient, are often cited as a cause of vertigo. Such isolated involvement is difficult to document, and vertebrobasilar insufficiency should not be diagnosed without associated brainstem symptoms and signs. Please see discussion of central causes of vertigo, below, for further discussion of brain stem ischemia.

CENTRAL NEUROLOGIC CAUSES{Back to Outline}

Central pathological causes of vertigo result from dysfunction of the vestibular portion of the VIII nerve, the vestibular nuclei within the brainstem and their central connections. (Table 4):

Neural connections with the central vestibular nuclei include interaction with the vestibular portions of the cerebellum (primarily the cerebellar flocculus); the visual sensory system; and afferent connections from muscle, joint, and tactile receptors. Normal persons will experience physiological vertiginous sensations when visual and vestibular inputs are in conflict or when they are initially exposed to heights. Central pathological causes of vertigo are less common than either peripheral or systemic causes, the vertiginous symptoms are usually less prominent, and additional neurological signs are usually present on examination.

Brainstem Ischemia and Infarction{Back to Outline}

The posterior circulation supplies blood to the brainstem, cerebellum, peripheral vestibular apparatus, in addition to other structures. It is not surprising that vertibrobasilar insufficiency may be accompanied by vertigo. In general, brainstem TIAs should be accompanied by neurologic symptoms or signs, in addition to vertigo or dizziness before a clear-cut diagnosis is entertained. However, it is clear that isolated episodes of vertigo lasting many minutes, may be due to posterior circulation dysfunction (Grad and Baloh, 1989, Oas and Baloh, 1992). Symptoms include transient clumsiness, weakness, loss of vision, diplopia, perioral numbness, ataxia, drop attack, and dysarthria (Amarenco, 1991; Caplan 1993). Common signs of vertebrobasilar ischemia include disorders of motor function such as weakness, clumsiness, or paralysis. A crossed defect (a motor or sensory deficit on one side of the face and the opposite side of the body) is good evidence of brainstem dysfunction. If the occipital lobes are the site of ischemia, transient visual loss in the form of complete or partial homonymous hemianopia will occur. Ataxia, imbalance, unsteadiness, or disequilibrium not necessarily associated with spinning vertigo may occur because of labyrinthine or cerebellar ischemia.

However, it is incorrect to believe that dizziness must be present before a TIA of the posterior circulation can be diagnosed. Isolated symptoms like those described may occur without dizziness. On the other hand, it has been overemphasized that such symptoms must always accompany dizziness, when the vertiginous symptoms are due to brainstem TIA. In elderly patients with no laboratory evidence of peripheral vestibulopathy or systemic disease, episodic disequilibration or dizziness may be due to vertebrobasilar disease (Grad and Baloh, 1989).

Sudden hearing loss with moderate dizziness may be due to infarction in the distribution of the internal auditory artery. In isolation, this symptom complex is uncommon in elderly patient with atherosclerotic vertebrobasilar disease, and is more suggestive of diseases affecting small and intermediate-diameter arteries such as syphilis, systemic lupus erythematosus, or periarteritis nodosa. In the atherosclerotic patient, such symptoms are usually accompanied by other signs of brainstem or cerebellar dysfunction, which allow a more certain diagnosis. If actual brainstem infarction occurs, neurological signs are often present on examination. Such signs may not be obvious and should be carefully sought. They include nystagmus of the central type, hyperreflexia, internuclear ophthalmoplegia, homonymous visual field defects, dysarthria, vertebral bruits, and ataxia (Leigh and Zee, 1991). Symptoms of dizziness are also quite common in proximal extracranial occlusion of the vertebral arteries (Caplan 1993) and in the subclavian steal syndrome.

Up to this point, the emphasis has been on the accompanying signs and symptoms that almost always occur with vertebrobasilar disease. It is noteworthy, however, that acute severe vertigo, mimicking labyrinthine disease, is an early symptom of acute cerebellar infarction in the distal territory of the posterior inferior cerebellar artery (Amarenco 1991). To differentiate this condition from labyrinthine disease, particular attention is directed to the type of nystagmus that is present. Acute peripheral vestibulopathy usually causes unidirectional nystagmus, with the fast phase in the opposite direction. This is similar to the mnemonic COWS (Cold, Opposite, Warm, Same) for remembering the direction of the nystagmus fast phase during thermal irrigation of the ear. The fast phase is away from the side of the cold water irrigation. Cold water mimics a peripheral destructive lesion of the labyrinth, and almost all lesions are destructive. Therefore, with a peripheral labyrinthine disturbance, the nystagmus fast phase is in the opposite direction or away from the involved ear. The nystagmus increases during gaze in the direction of the fast phase or contralateral to the peripheral vestibulopathy. Swaying or falling occurs toward the side of the lesion (opposite the nystagmus fast phase). The nystagmus direction is said to be fixed in that it tends to be uni-directional, away from the side of the peripheral vestibulopathy and tends to remain horizontal on upward gaze.

However, in certain syndromes of the posterior circulation, the initial presentation with acute vertigo suggests peripheral vestibulopathy. With incipient cerebellar infarction the sway or fall is toward the side of the lesion. The accompanying nystagmus may be variable in direction but is most prominent during gaze toward the lesion. In other words, with central lesions the fast phase of the nystagmus is in the direction of gaze (direction changing nystagmus) but becomes more prominent when gaze is directed ipsilateral to the lesion (Troost, 1996, Oas and Baloh 1992). Ocular motor findings are often present in brainstem disease, such as limitation of vertical gaze, upbeat or downbeat nystagmus or disconjugate nystagmus.

Multiple Sclerosis{Back to Outline}

Multiple sclerosis should only be diagnosed following the documentation of disseminated CNS lesions such as optic neuritis, transverse myelitis, internuclear ophthalmoplegia or other brainstem signs, and MRI changes. Occasionally, signs and symptoms suggestive of multiple sclerosis, including disequilibration and dizziness, may be mimicked by an intrinsic brainstem tumor in a young patient.

Cerebellopontine Angle Tumors{Back to Outline}

Tumors of the cerebellopontine angle rarely present solely with episodic vertigo. The most common tumor in this location results from a proliferation of the Schwann cells, hence the name schwannoma. Most of these tumors arise on the vestibular portion of the VIII nerve within the internal auditory canal. They progressively enlarge, deforming the internal auditory meatus and compressing adjacent neural structures such as the acoustic portion of the eighth nerve, facial nerve, trigeminal nerve, brainstem and cerebellum. Other tumors occurring in the cerebellopontine angle include meningiomas, epidermoids and metastases.

The most common symptoms associated with eighth nerve tumors are progressive hearing loss and tinnitus. Vertigo occurs in approximately 20%, but a symptom of imbalance or disequilibration is more common. Rarely a patient with a vestibular nerve tumor may present with subtle hearing loss, tinnitus and episodic vertigo. All those with progressive unilateral hearing loss, and particularly those with any vestibular symptoms should be carefully examined for additional neurological signs such as a depressed corneal reflex.

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