Clinical update
The lack of dizziness: bilateral vestibulopathy T
Dr Vincent Seet, Neurologist and Neuro-otologist, SCGH, Nedlands. Ph 9346 3333
he complaints of dizziness and vertigo have an estimated community prevalence of 22.9% and incidence of 3.1% per annum, with about half vestibular in origin. However, a subgroup of those with definite vestibular pathology can be misdiagnosed or suffer delays in diagnosis beyond 24 months – those with bilateral vestibular loss (bilateral vestibulopathy), where vertigo (i.e. spinning or another illusion of motion) is absent and in whom standard neurological examination that ignores four key steps will completely miss the diagnosis.
Suggestive history Bilateral vestibulopathy affects both sexes equally with mean age of about 60 (range 12-98 years). Patients typically present with ataxia worsened by darkness or uneven surfaces (i.e. where there is loss of visual and proprioception cues). They do not have symptoms of cerebellar disorders or peripheral neuropathy (e.g. dysarthria, upper limb incoordination, distal limb numbness) yet may find it necessary to use a walking aid for a gait ataxia that remains unexplained. About half the patients voluntarily complain of oscillopsia. A common description of this is the bobbing of the horizon or an inability to read road signs during locomotion, which reflects dysfunction of the vestibulo-ocular reflex and is similar to walking and looking at the environment through a camera. However, patients with a slowly progressive course and elderly patients who move slowly with limited head movements, may not complain of oscillopsia. While patients with bilateral vestibulopathy do not complain of vertigo, one third have a past history of vertigo.
Key examinations There are four key examinations for bilateral vestibulopathy, used in combination: 1. A tandem Romberg’s test. The patient is asked to place one foot directly in front of the other and then close the eyes. A positive test equates to a prevented fall in less than 6 seconds. This test is sensitive but not specific (i.e. it is also positive in cerebellar, peripheral nerve and central gait disorders such as Creutzfeldt-Jakob disease and Friedreich’s ataxia). 2. The dynamic visual acuity test. Static binocular visual acuity is first tested using a standard eye chart, then repeated while moving the head horizontally at 2 Hz and 30 degrees to either side. A loss of 3 or more lines is a positive test and suggests impairment of the vestibuloocular reflex (e.g. patients with acute bilateral vestibular loss often do far worse than the loss of 3 lines whereas patients with complete unilateral vestibulopathy score normally).
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3. The fundoscopic (vestibulo-ocular reflex) VOR test. The patient is asked to fixate on a target. Using an ophthalmoscope, the examiner observes for any slip in the optic disc during small head oscillations. In normal individuals, there is no movement of the optic disc during head movements. There is very low rate of false positives with this objective test. 4. Head impulse test. During visual fixation, the patient’s head is moved rapidly 20 degrees to either side. Impairment of the vestibulo-ocular reflex is confirmed when there is a catch-up or corrective saccade back to the fixation target. There is no corrective saccades in patients with a normal VOR, as it is a very fast reflex at 10 ms compared to 100 ms for the visual system. In bilateral vestibulopathy, corrective saccades towards the target are visible with head movements to either side. (Avoid this test in patients with significant cervical pathology).
disease, meningoencephalitis and sequential vestibular neuritis, which account for a further 25%. Why is diagnosis important? Diagnosis of bilateral vestibulopathy should lead to prompt general treatment such as vestibular physiotherapy and falls prevention. It will help the clinician avoid the common mistake of prescribing vestibular suppressants to a patient with bilateral vestibulopathy. It avoids the damaging misdiagnoses of a psychological disorder such as malingering or normal ageing. And it offers up treatment of the underlying cause in many cases, with genetic implications in some cases (e.g. spinocerebellar ataxia), and legal ramifications in others (e.g. gentamicin ototoxicity). Table 1. Causes of bilateral vestibulopathy Cause
Percentage
Idiopathic
47-50%
Ototoxic antibiotic e.g. gentamicin
13%-19%
Vestibular tests
Meniere’s disease
7%-12%
The gold standard test for bilateral vestibulopathy is now the rotational chair test. It negates the various disadvantages of caloric testing (i.e. technical and anatomical factors), with no dependence on satisfactory heat transfer to the horizontal canal, an ability to test frequencies ranging from 0.01Hz to 1.28 Hz (compared to 0.003 Hz only) and it is also useful for monitoring progress over time.
Meningoencephalitis
2-5%
Sequential vestibular neuritis
4%
SCA-3, SCA-6, EA-2, MSA
1-4%
Systemic autoimmune disease
1-3%
B12/folate deficiency
2%
Trauma
1-2%
Creutzfeldt-Jakob disease
1%
Cogan’s syndrome
1%
Vestibular evoked myogenic potential (VEMP) is useful in some patients who have suspected bilateral vestibulopathy and normal caloric test. While the caloric and rotational chair tests assess function of the horizontal canals and the superior vestibular nerve, VEMP is able to assess the function of saccule and inferior vestibular nerves.
Familial
1%
NF-2 bilateral acoustic neuroma; Superficial siderosis; Otosclerosis; Alcohol; Posterior circulation ischaemia; Bilateral chronic otitis media
<1% each
Computerised dynamic posturography, dynamic visual acuity and head impulse tests are also available.
Aetiology vs treatment Ideally, the identification of bilateral vestibulopathy should include the diagnosis of the cause but as Table 1 shows, among the variety of causes, ‘idiopathic’ makes up the majority (50%). Other important causes include drug ototoxicity, Meniere’s
SCA = Spinocerebellar ataxia, EA = episodic ataxia, MSA = multiple systems atrophy Suggested reading Zingler VC, Cnyrim C Jahn K Weintz E, Fernbacher J, Frenzel C, Brandt T, Strupp M. Causative, factors and epidemiology of bilateral vestibulopathy in 255 patients. Ann Neurol 2007;61:524-532. Kim S, Oh YM, Koo JW Kim JS. Bilateral vestibulopathy: Clinical characteristics and diagnostic criteria. Otology and Neurotology 2011;32:812-817.
Author competing interests: No relevant disclosures. 39