The author explains the clinical presentation, pathophysiology, prevention, diagnostic work-up, and management of bilateral vestibulopathy. Gait ataxia and oscillopsia are the key clinical features of bilateral vestibulopathy. Other clinical features of bilateral vestibulopathy include absence of spontaneous vertigo and nystagmus; inability to walk in the dark or on uneven or soft surfaces, unless by holding on to the wall or objects in the room (ie, use of contact cues); Romberg sign; no dysmetria or dysdiadochokinesis; insensitivity to motion sickness; a bilateral, usually symmetric, decreased sensitivity to caloric and rotational stimulation; and decreased or absent ocular counter-rolling. The most common causes of bilateral vestibulopathy are ototoxic aminoglycosides, Ménière disease, and meningitis. Clinicians should be particularly aware of risk factors for aminoglycoside-induced ototoxicity, including family history of ototoxicity, high serum levels, higher total dose, longer duration of therapy (beyond 7 to 10 days), intrathecal administration, previous exposure to ototoxins, concomitant use of other nephrotoxic or ototoxic drugs, renal impairment, fever, and older age. An imperceptible level of galvanic vestibular stimulation, delivered as zero-mean current noise (so-called noisy galvanic vestibular stimulation), may be effective in improving postural stability in patients with bilateral vestibular dysfunction.
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• Bilateral vestibulopathy has 2 primary modes of presentation: insidious (subacute) symmetric bilateral vestibulopathy and sequential unilateral vestibulopathy.
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• Gait ataxia and oscillopsia are the key clinical features of bilateral vestibulopathy.
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• Corrective saccades after rapid head turns to either side (ie, the head-thrust test) can be helpful in the diagnosis of bilateral vestibular dysfunction.
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• Risk factors for aminoglycoside-induced ototoxicity include: family history of ototoxicity, high serum levels, higher total dose, longer duration of therapy (beyond 7 to 10 days), intrathecal administration, previous exposure to ototoxins, concomitant use of other nephrotoxic or ototoxic drugs (eg, vancomycin, loop diuretics, cis-platinum, metronidazole), renal impairment, fever, and older age.
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• Prevention of aminoglycoside-induced vestibulotoxicity is essential, because the hair cells do not regrow after vestibulotoxic insults; hence, vestibular function does not recover. Instead, the limited compensation that occurs after bilateral vestibulopathy is generally achieved by augmentation of visual and proprioceptive reflexes.
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• An imperceptible level of galvanic vestibular stimulation, delivered as zero-mean current noise (so-called noisy galvanic vestibular stimulation), may be effective in improving postural stability in patients with bilateral vestibular dysfunction.
Historical note and terminology
In the late 19th century, several investigators studied the manifestations of absent labyrinthine function in deaf-mute patients (76; 69). Observations made of such patients included dysequilibrium, ataxia, absence of vertigo during or after rotation, reduced caloric and rotation-induced nystagmus, and resistance to seasickness. In 1882, American psychologist and philosopher William James (1842-1910) reported that deaf-mutes were resistant to the development of seasickness, providing further evidence that the vestibular apparatus was somehow involved in the pathophysiology of this condition (76; 95; 96).
Of 519 deaf-mutes tested, 186 were totally insusceptible of being made dizzy by whirling rapidly round with the head in any position whatever. In contrast, nearly 200 students and instructors at Harvard were similarly examined as controls, and but a single one remained exempt from the vertigo.
With the widespread use of streptomycin in the late 1940s, clinicians began to recognize the full clinical syndrome of acquired bilateral vestibulopathy. Some patients treated with streptomycin for tuberculosis developed severe ataxia and oscillopsia (04). The clinical features of these patients resembled those described earlier by neurosurgeon Walter Dandy in patients with Ménière disease who underwent bilateral vestibular nerve section.
Division of both vestibular nerves is attended by 1 rather surprising after effect, jumbling of objects (visual) when the patient is motion. As soon as the patient is at rest, the objects are again perfectly clear. The other disturbance is uncertainty when the patient is walking in the dark. Both of these effects persist, though with gradual lessening in severity (34).
Similar observations following bilateral vestibular nerve section had been reported even earlier by Ford and Walsh in a surgical patient of Dandys; therefore, it is not clear whether Dandy, or Ford and Walsh made the original observations (47; 91). Similar observations in nonsurgical patients were also made by Levin before Dandy's report (98).