BEDSIDE NEURO-OTOLOGICAL EXAMINATION AND INTERPRETATION OF COMMONLY USED INVESTIGATIONS

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1 iv32 BEDSIDE NEURO-OTOLOGICAL EXAMINATION AND INTERPRETATION OF COMMONLY USED INVESTIGATIONS Correspondene to: Dr Rosalyn Davies, The National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK; rosalyn. T RDavies J Neurol Neurosurg Psyhiatry 2004; 75(Suppl IV):iv32 iv44. doi: /jnnp he assessment of the patient with a neuro-otologial problem is not a omplex task if approahed in a logial manner. It is best addressed by taking a omprehensive history, by a physial examination that is direted towards deteting abnormalities of eye movements and abnormalities of gait, and also towards identifying any assoiated otologial or neurologial problems. This examination needs to be mindful of the fators that an ompromise the value of the signs eliited, and the range of investigative tehniques available. The majority of patients that present with neuro-otologial symptoms do not have a spae oupying lesion and the over reliane on imaging tehniques is likely to miss more ommon onditions, suh as benign paroxysmal positional vertigo (BPPV), or the failure to ompensate following an aute unilateral labyrinthine event. The role of the neuro-otologist is to identify the site of the lesion, gather information that may lead to an aetiologial diagnosis, and from there, to formulate a management plan. BACKGROUND Balane is maintained through the integration at the brainstem level of information from the vestibular end organs, and the visual and proprioeptive sensory modalities. This proessing takes plae in the vestibular nulei, with modulating influenes from higher entres inluding the erebellum, the extrapyramidal system, the erebral ortex, and the ontiguous retiular formation (fig 1). Therefore any derangement of the struture or funtion of the sensory inputs, the entral vestibular strutures or the effetor pathways that is, the oulomotor and vestibulospinal pathways is likely to result in a balane disorder. Many onditions will elude diagnosis if balane is equated purely with a disorder of vestibular funtion. Drahman and Hart 1 have emphasised the importane of multi-sensory dizziness, partiularly in the elderly, when two or more of the following onditions are present: visual impairment, peripheral neuropathy, vestibular defiit, ervial spondylosis, and orthopaedi disorders affeting the large joints. An appreiation that dysequilibrium may be onsequent on multiple pathologies is essential if the appropriate investigation and interpretation of the data are to be ahieved. General medial onditions similarly may ontribute to dizziness that is, postural hypotension, vasovagal synope, ardia valvar disease, hyperventilation and a full and omprehensive history is vital. A general medial examination, with partiular attention to the eyes, the ears, the nervous system, the ardiovasular system, and the loomotor system, may be indiated and general medial investigations should also be onsidered. SECTION 1 Aural examination A areful inspetion of the ear is needed, as any otologial pathology is likely to point the liniian to a peripheral rather than a entral neuro-otologial lesion. It inludes examination of the aurile, the external auditory meatus, and the middle ear that is, as far as an be assessed by examination of the tympani membrane (TM). The tympanum offers a window into the middle ear left and is affeted by most of the hanges that an take plae in the middle ear. Otitis externa, aute otitis media or TM perforation ontraindiate alori testing. Wax also preludes alori irrigations beause it ats as a heat seal, and also when impated gives rise to a spurious ondutive hearing loss. Inspetion of the ear may be arried out with the use of an otosope or with a head-worn light soure, leaving the hands free. The speulum should be direted around the irumferene of the outer ear anal looking for debris, foreign bodies, inflammation, and for defets of the posterior or anterior wall. The magnifying lens of the Siegel s (or pneumati) speulum an be fitted into the speulum and the bulb squeezed to raise intrameatal pressure and then relaxed, suking the membrane outwards. In the presene of a middle ear effusion, the membrane is immobile; however with a very flaid TM, this may have been suked bak onto the middle ear muosa, and

2 NEUROLOGY IN PRACTICE Vision Proprioeption Vestibular labyrinths Higher entres Extrapyramidal system Cerebellum Retiular formation Brain stem integrating entres lowering the pressure may suk it out again, allowing a retration poket to be distinguished from a perforation. Alternatively, the Valsalva manoeuvre that is, auto-inflation of the ear an be used to raise middle ear pressure and to observe similar hanges. Examination of the aurile (pinna) The aurile is essentially vestigial, ontributing only to olletion of sound, slightly enhaning the effiay of the ear. It should be inspeted for signs of inflammation, trauma, surgial sars, or haematoma auris following a blow to the ear, and also for ongenital deformities. Most developmental abnormalities are fairly obvious, but must be arefully identified beause of the likely assoiated findings of middle and inner ear abnormalities that is, anotia (absent aurile); mirotia (smaller than normal and probably misshapen aurile). Pre-auriular appendages are found in 1.5% of the population; fistula auris, a small blind pit seen anterior to the tragus, results from inomplete fusion of the auriular tuberles. Examination of the external auditory meatus Congenital onditions inlude a stenosed or atreti external auditory meatus (EAM). In the latter, the EAM is losed over with a membranous, straight bony wall aross the anal. This abnormality an be graded aording to severity and radiologial investigation needs to be pursued if found, to identify the size and shape of the middle ear avity, and possibility of assoiated inner ear disorders. Aquired abnormalities inlude: Foreign body obstrution Otitis externa. Likely infetions: staphyloous, pseudomonas and diphtheroids; fungal infetions that is, aspergillus and andida; and viral infetions, identified by the vesiular eruptions of herpes zoster that is, Ramsey-Hunt syndrome Osteomas are rounded exresenes of bone Exostoses are small osteomata and are quite ommon in people who swim or dive regularly. Examination of the tympani membrane and middle ear Wax If impated, or obsuring the view of the tympani membrane, the erumen must be removed arefully without ausing pain to the patient. Hard lumps an be removed Syringing Pereption of orientation Oulomotor system Antigravity musles of posture Figure 1 Sensori-motor physiology of the maintenane of balane showing the three sensory inputs required for maintenane of equilibrium, the entral modulating influenes, and the efferent pathways. Absolute ontraindiations to syringing The presene of an ear infetion (otitis externa or media) The ear is known to have a perforation From the history, the ear is suspeted to have a vulnerable tympani membrane Method (1) With the patient seated in a hair, protet him/her with a plasti ape and towel (2) Ask the patient to hold a kidney dish reeiver on the shoulder, just below the pinna (3) Draw up in a metal syringe a solution of sterile water of 37 C (any variation from this will ause vertigo) (4) Draw the pinna upwards and bakwards (5) Plae the nozzle a few millimetres into the anal, pointing upwards and bakwards (6) Diret the stream of water along the roof of the anal, between the skin and the wax Note: Syringing should not be painful and should be stopped if the patient omplains of pain With appropriate instrution, nursing staff an arry out this proedure Aural sution in the hands of an otologist may be required if the wax is not easily removed by the above measures iv33

3 iv34 using the Jobson-Horn probe, or a Cawthorne wax hook. An alternative method for removing wax is syringing. If the wax seems very hard, it an be softened over a period of weeks using warm olive oil drops administered nightly, or alternatively 5% sodium biarbonate drops, or a eruminolyti preparation available ommerially. Tympani membrane and middle ear The standard landmarks of the tympani membrane (TM) are: the entral portion with handle of the malleus visible through the drum; the pars flaida superiorly, and the pars tensa inferiorly; identifiation of the long proess of the inus and the stapedius tendon seen in more TMs. The following are important features to identify: Perforations when seen in the pars tensa, these are lassified as marginal or entral; defets of the atti portion are desribed as atti perforations; and the position of the perforation is defined as anterior, inferior, or posterior; large entral perforations are desribed as subtotal and large marginal perforations as total. Colour the normal eardrum has the appearane of mother of pearl. The light reflex is found antero-inferiorly, where refletion of the examination light ours. If the membrane is thikened, the reflex may be lost. If the middle layer of fibrous tissue of the TM undergoes hyaline degeneration it may beome impregnated with deposits of alium that is, tympanoslerosis. Position of the membrane Retration of the membrane ours when there is hroni lowering of pressure in the middle ear that is, hroni obstrution of the Eustahian tube. The handle of the malleus is drawn inward and there is retration of the drum toward the medial wall of the middle ear. When severe, the drum is strethed around the long proess of the inus and head of stapes, and at worst, the membrane is plastered against the promontory. (A fluid level may be visible if seretory otitis media has resulted from redution of middle ear pressure. In the presene of air bubbles, middle ear fluid is onfirmed.) With raised middle ear pressure, the drum may bulge outwards and depending on the olour, this inreased middle ear pressure may be aused by aute suppurative otitis media (herry red), or if a normal olour, the bulge is likely to be aused by raised air pressure in the middle ear alone. Disorders of the tympani membrane and middle ear Congenital abnormalities inlude fusion of the ossiles that is, ongenital stapes fixation, absent stapedius tendon, and unovered or aberrant VIIth nerve. Aquired disorders inlude aute otitis media (fig 2), hroni otitis media, holesteatoma, serous otitis media, and ossiular abnormalities. Cholesteatoma is a yst lined with squamous epithelium, whih an arise in ears undergoing long periods of negative middle ear pressure and persisting middle ear infetion that is, hroni suppurative otitis media. Cholesteatomatous ysts are likely to begin in the atti of the ear and extend into the mastoid antrum. They are filled with ast-off epithelial ell debris and slowly inrease in size. They an erode the surrounding bone and produe intraranial ompliations by eroding through the dura of the middle or posterior fossa, or through the lateral sinus or into the lateral semiirular anal (when a positive fistula sign would be eliited, see below). Cholesteatoma an be diagnosed from a history of perforation, hroni foul smelling disharge from the ear, and NEUROLOGY IN PRACTICE Figure 2 Aute otitis media: otosopi appearane of left tympani membrane. Reprodued with permission of Professor Anthony Wright, Institute of Laryngology and Otology, London. keratin debris in the pars flaida area on otosopi examination. It is potentially serious and requires surgial removal. Tubo-tympani disease desribes hroni ative otitis media unassoiated with holesteatoma. It is haraterised by reurrent infetions rather than persistent infetions and by odourless disharge rather than offensive disharge. A entral TM perforation and a break in the ossiular hain or malleus fixation are regarded as safe and unlikely to be assoiated with holesteatoma. Serous otitis media is reognised by an air/fluid level in the middle ear, or a bluish disolouration of the drum. A lak of ompliane of the drum is found on tympanometry. Other effusions into the middle ear inlude blood (for example, haemo-tympanum after head trauma) or erebrospinal fluid within the middle ear spae. Otoslerosis This is an inherited, autosomal dominant hearing disorder, tending to present in later hildhood/adulthood. Deposition of bone in the oval window nihe ours leading to fixation of the stapes footplate and a ondutive hearing loss. The otosleroti proess an extend to involve the oti apsule, leading to an additional sensori-neural hearing loss and vertigo. Typially in the early osteoblasti phase, the appearane of the malleus head is hyperaemi that is, Shwartze s sign. Glomus tumour This is a jugulo-tympani paraganglionoma whih tends to expand within and traverse the petrous temporal bone by way of the pneumatised air ell trats. It an present with pulsatile tinnitus, and a vasular mass lying behind the tympani membrane an be identified (also desribed as the setting sun sign). These tumours may also extend into the labyrinth, or present as ranial nerve abnormalities. TESTING OF AUDITORY FUNCTION Tuning fork tests Tuning fork tests have been traditionally used to distinguish ondutive from sensorineural hearing loss and to identify funtional hearing loss. With the advent of pure tone audiometry, only a few of these tests are still used linially. The priniples of tuning fork tests are:

4 NEUROLOGY IN PRACTICE Fistula sign This is eliited in those patients where transmission of air pressure hanges from the EAM is possible through a fistula into the labyrinth: raised pressure auses a onjugate deviation of the eyes towards the opposite ear and with maintenane of pressure, a orretive fast eye movement will be introdued. the nystagmus will be towards the affeted ear Depending on where the fistula has developed, the nystagmus will be: horizontal (horizontal semiirular anal) torsional (anterior anal) vertial (posterior anal) EAM pressure may be raised by tragal pressure, but more aurately by tympanometry. Hennebert s sign is a positive fistula sign in the presene of an intat TM. the inner ear is more sensitive to sound onduted by air than bone in pure ondutive hearing loss, the affeted ear is subjet to less environmental noise and is more sensitive to bone onduted sound. The most ommonly used tuning forks are those at 256 and 512 Hz. Lower frequenies produe a vibrotatile stimulus whih an result in misleading thresholds. In pratie the 256 Hz tuning fork better distinguishes air bone gaps than the 512 Hz fork. When performed, the prong (tine) of the tuning fork should be struk against a hard, but elasti, mass (for example, a rubber pad) to prevent prodution of Rinne s tuning fork test Heinrih Rinne desribed his tuning fork test in 1855 (1) The fork is struk and held with the tines perpendiular to the long axis of the external auditory meatus with the losest tine 1 m from the entrane to the meatus (2) The patient is asked to report if he an hear the sound (AC) (3) The fork is immediately transferred behind the ear with the base firmly pressed to the bone overlying the mastoid (BC) (4) The patient is asked whih sound is louder: that in front of the ear, or that behind the ear Positive Rinne test: ifac. BC that is, the sound in front of the ear is reported as louder: indiates normal hearing or an ear with a sensorineural hearing loss. Negative Rinne test: ifbc. AC that is, the sound in front of the ear is reported as quieter: identifies a signifiant ondutive omponent of hearing loss of. 15 dbhl BUT, a false positive Rinne an our if there is a severe sensorineural hearing loss in the tested ear, as the BC stimulus is heard in the non-tested ear beause of transranial transmission, and thus will be louder than AC sound. This an be overome by masking the nonaffeted ear with a Barany noise box. The Rinne test has a high speifiity for ondutive hearing loss, but a low sensitivity, this not reahing 90% until the air bone gap. 30 db Weber stuningforktest The aim of Ernst Weber s test (1934) is to identify the better hearing ohlear. It is used in onjuntion with Rinne s test and is of most use in patients with unilateral hearing loss: (1) The 512 Hz tuning fork is struk and plaed to the head in the midline, either at the vertex or on the forehead (2) The patient is asked to say whether the sound is heard better in one ear, or equally in both ears A entral Weber is desribed if the tone is heard entrally identifies a normal hearing patient A lateralising Weber is when the tone is heard to one side identifies the side of the better hearing ohlear BUT, if there is a ondutive omponent to the hearing loss, the tone may be heard in the poorer hearing ear (see Rinne s test) The results need to be interpreted with are and only in onjuntion with further hearing tests. overtones, two thirds of the way along its tines to minimise distortion produts. The linial findings desribed above will point to the appropriate test battery to investigate further any assoiated hearing loss. Pure tone audiometry shows the existene and extent of hearing loss and allows determination of whether the loss is ondutive, or sensorineural, or both. It requires the ooperation of the subjet and as suh is a subjetive estimate of hearing thresholds. As a psyho-aousti measurement, the results of audiometry may be biased by partiular methods of onduting the test, and so a well defined proedure must be adopted. If the patient is unable or unwilling to ooperate, additional audiologial investigation will be neessary to provide objetive measures of hearing. These additional tests inlude measurement of otoaousti emissions, stapedius reflex threshold measurement, and brainstem auditory evoked responses. The purpose of aural admittane testing that is, tympanometry is the objetive determination of middle ear pressure, the measurement of stati aousti impedane, and haraterisation of the tympanometri shape. High impedane abnormalities inlude a perforated tympani membrane, middle ear effusion, retrated tympani membrane, or ossiular fixation. Low impedane abnormalities inlude thin atrophi tympani membranes and ossiular disruption following head trauma. SECTION 2 Clinial examination of eye movements Examination of the eye movements requires optimal onditions. There should be good lighting with the patient sitting omfortably, head eret. The liniian should be aware of the visual auity of both eyes, using the Snellen hart at 6 m. The eyes should be in the primary position of gaze and the visual target held at a distane just greater than the patient s foal point. Cover test for strabismus The presene of a manifest or a latent strabismus needs to be determined. Either an ause an abnormal eye movement examination beause of hanging opti fixation from one eye to the other. When one eye has beome amblyopi, the other eye should be assessed for both linial and eletronystagmagraphi purposes. To perform the over test, eah iv35

5 iv36 eye is overed in turn, either with the hand or a piee of ard, lose to the eye to prevent opti fixation of the overed eye. The patient is asked to fixate on a visual target and then the overed eye observed as the over is taken away. (1) Manifest strabismus/exotropion is identified when the affeted eye is turned outwards during normal gaze. An esotropion is identified when the eye is turned inward during normal gaze. (2) An exophorion in the overed eye is identified when the overed eye moves inward as the over is removed. An esophorion is identified as the overed eye moves outwards with re-fixation. (3) Latent nystagmus is identified when nystagmus is seen in the unovered eye during over testing. Typially, the nystagmus beats away from the overed eye and is onjugate. Latent nystagmus an be uni- or bilateral and is ongenitally determined. In some patients it an be assoiated with ongenital nystagmus (vide infra). Range of eye movements The eyes are examined for range in both horizontal and vertial planes to a limit of 30 from the midline. The eye movements are onjugate if both eyes move together. If the movements are onjugate but the range is not full, the patient may have a gaze paresis. Gaze paresis A gaze paresis ours if there is a restrition in the range of eye movements, in one or more diretions. It may be nulear or supranulear, with referene to the oulomotor nulei within the brainstem: ontralateral horizontal gaze paresis ours in lesions of the frontal eye fields in the ortex ipsilateral gaze paresis may identify a lesion of the tegmentum, or of the ponto-medullary or ponto-mesenephali juntions supranulear gaze palsy an be seen in mesenephali lesions, in whih there is loss of volitional gaze, with vertial movements being lost before horizontal. This is identified by finding a full range of eye movements in response to involuntary reflex testing that is, vertial vestibulo-oular reflex (VOR) testing. Oular paresis Where there is a dissoiation of eye movements that is, they are dysonjugate an oular paresis is likely. The patient s eyes should be examined for IIIrd, IVth, and VIth nerve palsies: (1) The oblique musles are tested when the eyes are adduted; the superior oblique, through its pulley system, will lower the eye and onversely the inferior oblique will elevate the eye (2) The retus musles are tested with the eye abduted, with the inferior retus lowering the eye and the superior retus elevating the eye. An oular paresis may be aused by a retro-orbital spae oupying lesion or by involvement of the extra-oular musles that is, thyroid eye disease, mitohondrial ytopathy or manifest strabismus. Lesions of the IIIrd, IVth, and VIth ranial nerves, or their nulei, ause a paresis in the diretion of the pull of the musles they innervate: a lesion of the IIIrd ranial nerve auses the eye to be drawn down and out, and may or may not be assoiated with ptosis and a dilated pupil that is, if the lesion NEUROLOGY IN PRACTICE involves the parasympatheti fibres arried with the IIIrd nerve a lesion of the IVth ranial nerve auses the eye to be slightly elevated, leading to addution of the eye and a possible head tilt to the side to the lesion, to redue diplopia a lesion of the VIth ranial nerve auses a loss of abdution and again the head may ompensate by rotating towards the side of the lesion. Oular stabilising systems There are three visually ontrolled systems produing eye movements that stabilise gaze: the saadi system, the smooth pursuit system, and the optokineti system. The saadi system responds to error in the diretion of gaze by initiating a rapid eye movement to orret a retinal position error; the smooth pursuit system is responsible for maintaining gaze on a moving target by keeping the target within the visual field; the optokineti system is thought to be a more primitive form of smooth pursuit, involving the whole retina instead of the fovea alone. These systems an eah be tested and normal funtion is likely to indiate integrity of entral vestibular pathways. Saades This is a fast eye movement with a veloity between /seond, the veloity inreasing with inreased amplitude of eye movement. Saades an be voluntary or involuntary, the former used to move the eyes between visual targets in the shortest possible time; the involuntary saade maintains the target on the fovea when there has been slip of the retinal image, and is the fast phase of nystagmus. The saade may be visually triggered, as in optokineti nystagmus, or an be of vestibular or ervial origin, with a fast phase of nystagmus shifting the eyes in the diretion of the ongoing head movement before the slow phase ompensatory drift. Normal subjets are aurate up to a target jump of 20, above whih a small orretive saade is required to bring the fovea on target. Overshooting is rare. The normal saadi lateny before a new saade an be generated is 200 ms. The ability to generate saades depends on the integrity of projetions between the frontal eye fields, the audate nuleus, the substantia nigra retiulate, and the deep and intermediate layers of the superior olliulus. Projetions are then to the para-pontine retiular formation (PPRF) and from here to the ipsilateral abduens nerve nuleus and by the median longitudinal bundle (MLB) to the ontralateral oulomotor nuleus of the medial retus. The pretetal neurons also projet to the oulomotor nulei, both sets of neurons onneting to the vestibular nulei. Clinial assessment Saadi eye movements are assessed by asking the patient to look bak and forth between two targets in front of him/her, sited approximately 30 to the right and 30 to the left of the midline, respetively. Inreasing the distane between the targets beyond 30 inreases the hane of deteting a hypometri saade, while reduing the distane inreases the hane of deteting a hypermetri saade. Abnormalities of saadi eye movements Three variables are examined: saadi reation time (lateny), saadi veloity, and saadi auray. Abnormalities of any of these features may be aused by

6 NEUROLOGY IN PRACTICE entral nervous system (CNS) pathology or oular myopathy. Peripheral vestibular pathology does not ause abnormal saadi eye movements. Internulear ophthalmoplegia (INO) aused by a lesion of the ipsilateral MLB. May present as ataxi nystagmus, whereby adduting saades ipsilateral to the lesion are slower than abduting saades. Subtle early lesions an be revealed by eletronystagmography (ENG) reordings of separate eye saades, showing slowing of the adduting saade on the side of the lesion with a normal veloity, but a hypermetri abduting saade (fig 8) Lesion of PPRF this auses loss of all types of rapid ipsilateral movements and the eyes move to the ontralateral visual field. In response to vestibular or visual stimulation, the eyes display a toni ontralateral deviation with loss of the fast phase of nystagmus. One-and-a-half syndrome seen with extensive brainstem pathology affeting both the ipsilateral PPRF and the median longitudinal bundles. This syndrome an result with a failure of onjugate gaze in one diretion and an internulear ophthalmoplegia in the other. The pathways subserving vertial and horizontal saades are independent, suh that vertial saades are unimpaired by lesions of the PPRF, while lesions of the mesenephali retiular formation affet vertial saades exlusively. Cerebellar pathology may affet the auray of saades with undershooting (hypometria) and/or overshooting (hypermetria) ipsilateral to the side of the lesion. Hypermetria is more ommon in erebellar lesions than hypometria, while in intrinsi brainstem lesions, hypometria is more likely Supranulear degeneration MSA (Steele-Rihardson- Olszewski syndrome, Shy-Drager syndrome, progressive supranulear palsy, and Huntington s horea), saade reation time is prolonged. In these onditions, hypometria annot our. Vertial eye movements are usually affeted before horizontal, initially with upgaze more involved than downgaze and saades more affeted than pursuit Figure 3 text). Ative optokineti nystagmus Passive optokineti nystagmus Seonds Ative versus passive optokineti nystagmus (OKN) (see Figure 4 Optokineti stimulus (see text). Reprodued with permission from Jaeger Toennies, Wurzburg, Germany. Frontal pathology there may be hypometria or loss of horizontal saades, ontralateral to the side of the lesion. Vertial saades are not affeted. Smooth pursuit Smooth pursuit is responsible for maintaining gaze on a moving target so that the target is stabilised on the fovea. The gain of the pursuit system approahes unity at peak veloities of 30 /s or sinusoidal rotation at 0.1 Hz (Baloh et al 2 ). Above a peak veloity of 60 /s, or sinusoidal rotation at 1 Hz, the gain falls off rapidly and ath-up saades are observed that is, saadi intrusions and the pursuit is desribed as broken. The smooth pursuit and the vestibular oular reflex system are omplementary in stabilising the retinal image, with the pursuit system effiient at low target veloities, and the vestibulo-oular system effiient at high input veloities. Clinial assessment The smooth pursuit system an be examined linially by moving a target that is, the examiner s finger slowly bak and forth in a sinusoidal fashion, initially in the horizontal and then in the vertial plane, to a maximum of 30 displaement from the midline, at Hz. In hroni peripheral vestibular disorders, smooth pursuit is normal. Abnormalities Impairment of smooth pursuit may be aused by lesions of the fovea, of the alerine ortex, of the parieto-oipital ortex, the parieto-temporal region, the dorsolateral pontine nuleus, and the erebellar-floulus. The abnormality may be ipsilateral or bilateral. Pursuit eye movements are symmetrially affeted by age, psyhotropi mediation, alohol, antionvulsants, and vestibular and CNS sedatives. Optokineti nystagmus The funtion of optokineti nystagmus (OKN) is thought to be the stabilisation of the eyes relative to spae during slow head movements in the low frequeny range, ill served by the VOR for example, the person looking at the senery from a moving vehile. The optokineti system inludes the peripheral retina, the aessory opti trat, the vestibular nulei, and the retiular formation. There are two types of OKN (fig 3): iv37

7 iv38 RT Normal LT Reversed Normal Reversed Drum right Drum left Figure 5 Congenital nystagmus showing the optokineti response in a patient with ongenital nystagmus that is, reversal of OKN with the slow phase of the patient s eyes in the opposite diretion to the diretion of the OKN drum. Cortial optokineti nystagmus ative or look OKN, indued more through foveal input, and an be indued both by using a small drum and by a full field optokineti stimulus Subortial optokineti nystagmus passive or stare OKN, in whih it is believed that the peripheral retina is involved without partiipation of the erebral ortex Although the two traings appear similar, in the ative situation, the slow omponent veloity is similar to the speed of the drum that is, the gain approahes 1. Also, with reversal of the drum diretion, the eyes deviate in the diretion of the slow omponent that is, the same as the diretion of movement of the drum. However, in the stare ondition, subserved by the subortial pathway, the slow omponent veloity is onsistently less than drum veloity, and with drum reversal, the diretion of eye deviation is in the diretion of the fast phase of the nystagmus. Clinial assessment A qualitative assessment may be undertaken at the bedside or in the outpatient department using a small handheld or mehanially driven optokineti drum. This is a ylinder 30 m diameter that an be rotated to eliit nystagmus either in the horizontal or vertial plane, at speeds from 40 /s upwards. For quantitative purposes, more preise stimulus parameters are obtained by seating the patient inside a large, striped, rotating drum and stimulating the entire visual field (fig 4). Clinial abnormalities Peripheral lesions the imbalane of vestibular tone resulting from lesions of the labyrinth and VIIIth nerve an give rise to a diretional preponderane with the hand held drum. It is best seen with diret observation of the eyes with repeated abrupt reversal of the drum diretion. These abnormalities are rarely seen with full field OKN Central lesions abnormalities of OKN tend to mirror abnormalities of smooth pursuit, and abnormalities of fast omponents mirror abnormalities of voluntary saades. Lateralised lesions of the parieto-oipital region, brainstem and erebellum result in impaired OKN when the stimulus is moved toward the damaged side. Congenital nsyatgmus: reversal of OKN is a signifiant feature in many ases of ongenital nystagmus (fig 5). The nystagmus beats paradoxially in the opposite diretion to that antiipated from the diretion of drum movement. Assessment of nystagmus Nystagmus is a ombination of alternating slow and fast phase eye movements in opposite diretions. For linial purposes the diretion of nystagmus is defined by the fast phase. It an be physiologial or pathologial and pathologial nystagmus an be ongenital or aquired. In priniple, large amplitude nystagmus should be onsidered as entral in origin, and is only likely to be peripheral if seen in the first few days of vestibular neuritis or an aute episode of Menière s disease. Physiologial vestibular nystagmus The semiirular anal oular reflexes produe eye movements that ompensate for head rotations. With small amplitudes of head displaement, there is a slow ompensatory eye movement in the diretion opposite to rotation, serving to stabilise the gaze. With a larger stimulus the slow vestibular indued eye movement deviation is interrupted by a fast eye movement in the opposite diretion, generating physiologial nystagmus. This type of nystagmus an be indued both by rotary hair testing and alori irrigations but also by extremes of eye deviation that is, more than 30 laterally from the primary position (physiologial end point nystagmus). There is a relation between the magnitude of nystagmus and the state of arousal in human subjets during vestibular stimulation. A subjet who is allowed to daydream has a lower slow omponent veloity than the subjet who is asked to perform ontinuous mental arithmeti. Subjets experiening repeated angular aelerations for example, ie skaters and daners may display permanent habituation of the response with a redution or loss of nystagmus in response to vestibular stimulation. Pathologial vestibular nystagmus (spontaneous nystagmus) Spontaneous nystagmus results from an imbalane of toni signals arriving at the oulomotor neurones. Beause the vestibular system is the main soure of oulomotor tonus, it is the driving fore of most types of spontaneous nystagmus, hene the name vestibular nystagmus. There is a onstant A B Centre Centre Left 1se Left Dark Dark NEUROLOGY IN PRACTICE Figure 6 Peripheral versus entral nystagmus identifying the effets of gaze testing in a patient with: (A) a peripheral vestibular defiit the spontaneous nystagmus on gaze left is enhaned in the absene of opti fixation; (B) a gaze evoked nystagmus the nystagmus dereases in frequeny and slow omponent veloity in the absene of opti fixation.

8 NEUROLOGY IN PRACTICE Figure 7 The Dix-Hallpike manoeuvre (see text). drift of the eyes towards the side of the lesion, interrupted by a fast omponent in the opposite diretion. The lesion may our in the labyrinth, the vestibular nerve, or in the vestibular nuleus. Spontaneous nystagmus is invaluable in siting vestibular and neurologial disease. For full assessment, the nystagmi response produed by (1) hange of eye position, and (2) the presene or absene of opti fixation, needs to be doumented. Nystagmus is graded using Alexander s law: if it is only present when the eye is deviated towards the fast phase it is 1 ; if it is also seen in the primary position it is 2 ; and if it is also seen with the eye deviated towards the slow phase it is 3. The vestibular lesion may only be deteted with the removal of opti fixation if the lesion is small or ompensation at a entral level has ourred. This is an important riterion for identifying nystagmus aused by peripheral pathology that is, the nystagmus displays an inrease of amplitude with the removal of opti fixation and thus the nystagmus may be deteted in the dark by ENG or video-oulography. Gaze evoked nystagmus Patients with gaze evoked nystagmus are unable to maintain stable onjugate eye deviation away from the primary position. The eyes drift bakwards towards the entre with an exponentially dereasing waveform. Corretive saades onstantly reset the eye in the desired position, thus gaze evoked nystagmus is always in the diretion of gaze. In the absene of opti fixation, the frequeny and slow omponent of veloity derease (fig 6). Dysfuntion may be seondary to a lesion anywhere from the multiple brain entres ontrolling onjugate gaze to the neuromusular juntion. It is not Table 1 Comparison of benign paroxysmal positional nystagmus (BPPN) and entral positional nystagmus (CPN) BPPN CPN Latent period 2 45 seonds 0 seonds Adaptation Within 30 seonds Persisting Fatigability Disappears on repetition Persists Vertigo Present, sometimes severe Usually absent, or very mild Diretion of Torsional and geotropi Any nystagmus Inidene Common Rare aused by a peripheral vestibular lesion. Symmetrial gaze evoked nystagmus is ommonly observed following the use of antionvulsants, partiularly phenytoin and phenobarbitone, and ingestion of psyhotropi drugs and alohol. Asymmetrial horizontal gaze evoked nystagmus is likely to indiate a strutural brain lesion. Positional nystagmus Nystagmus an be eliited by ritial head positioning in ertain pathologial states. The Dix-Hallpike head manoeuvre (fig 7) is a valuable test in suh patients and an distinguish between the peripheral nystagmus of benign paroxysmal positional vertigo (BPPV), entral positional nystagmus, and atypial positioning nystagmus. The test onsists of: seating the patient appropriately on a ouh so that when supine, their head will extend over the end of the ouh the patient is asked to remove their spetales and is warned they may feel dizzy as a result of the test he is asked not to lose his eyes but to keep his gaze entred on the examiner s forehead the patient s head is turned towards the examiner, and moved rapidly into the lying position with the head hanging 30 over the bak of the ouh (in this way the posterior semiirular anal of the undermost ear is moved diretly through its plane of orientation) the patients eyes are observed for nystagmus for up to one minute the manoeuvre is repeated for both the right and the left ear undermost positions. Peripheral positional nystagmus (aused by BPPV) BPPV was first desribed by Barany in 1921 and is diagnosed using the Dix-Hallpike manoeuvre. With the pathologial ear under most, the Hallpike test produes the following lassial signs Latent period to onset of nystagmus from 2 45 seonds Development of torsional nystagmus with the fast phase towards the ground (geotropi) Assoiated vertigo and autonomi symptoms Adaptation of vertigo and nystagmus on maintaining the head hanging position Reversal of nystagmus on returning to the upright position Fatiguing of symptoms and signs on repeating the test. Central positional nystagmus Typially, there is no lateny to the onset of nystagmus, frequently no vertigo, and no adaptation of fatigability (table 1). The diretion of nystagmus may be towards the uppermost ear, or may be vertial in diretion. Multiple slerosis, Arnold-Chiari malformation, and erebellar vasular disease may produe positional nystagmus that may be the only sign of posterior pathology. Congenital nystagmus The patient with ongenital nystagmus rarely omplains of osillopsia, but has a entral eye movement abnormality. The nystagmus is in the horizontal plane and may hange diretion. There is a null point, whih is often the head position the patient adopts for reading; the slow phase is dysmorphi and may be exponential as demonstrated on the ENG, and harateristially there is reversal of OKN that is, the slow phase of OKN does not math the diretion of drum rotation. iv39

9 iv40 Periodi alternating nystagmus Periodi alternating nystagmus hanges diretion with a hange of head or eye position. Cyle length varies from 1 6 minutes with null periods of 2 20 seonds. The preise site of the lesion is known, but both the erebellum and the audal brainstem have been impliated. Torsional nystagmus This nystagmus is a rotation of the eye, beating around the visual axis. The diretion of beat is better speified in rightleft terms to avoid onfusion that is, lokwise nystagmus is as seen from the examiner s point of view. It is usually aused by a lesion in the area of the vestibular nulei on the opposite side to the beat diretion as in Wallenberg s syndrome. Pendular nystagmus This is seen in assoiation with longstanding or ongenital visual defets (when it is not assoiated with balane symptoms) or it an develop weeks to months after strutural brainstem disease. In the latter, patients usually show erebellar or pyramidal features and desribe osillopsia whih is largely unhanged by head movements. Monoular nystagmus by definition only ours in one eye and has been reported in a number of ophthalmalogial and neurologial onditions. Tests of stane and gait Romberg test The Romberg test was desribed in 1846 in patients with dorsal olumn loss as a result of tabes dorsalis. The test is desribed as positive when there is inreased body sway with the eyes losed when the patient is standing with his feet lose together. The priniple lying behind this test is that balane is maintained with minimal physiologial sway when all three sensory inputs are funtioning that is, vision, vestibular input, and proprioeptive input. With the loss of one or more of these inputs, there will be inreased physiologial sway. Unsteadiness on Romberg testing an also our with aute vestibular defiits and with erebellar disease, although in the latter, the effets of eye losure theoretially should not affet sway. Unterberger s test Unterberger desribed the tendeny of vestibular stimulation to turn the patient in the earth s vertial axis when walking. His test identifies that the diretion of turning in patients with unilateral vestibular defiits oinides with the diretion of past-pointing and falling that is, in the diretion of the slow omponent of nystagmus. The test is performed by asking the patient to stand with their arms extended and thumbs raised, and then to lose their eyes. The patient is asked to marh on the spot for about 50 steps and the angle of rotation as well as forwards and bakwards movements is reorded. There is, however, a pronouned variability in the rotation angle from one subjet to another and in the same subjet on repeated testing, and the outome should only be used in the ontext of the rest of the vestibular test battery. Gait test This is a 5 m walk, firstly with the eyes open and then with the eyes losed, with the patient walking at normal speed towards a fixed target and the examiner lose to one side for safety reasons. As with the Unterberger s test, patients with reent unilateral vestibular lesions tend to deviate towards the side of the lesion. This test is fraught with false negatives. Tandem gait test These tests are useful for assessing vestibulospinal funtion. When performed with the eyes open, tandem walking is primarily a test of erebellar funtion beause vision ompensates for hroni vestibular and proprioeptive defiits. Tandem walking with the eyes losed provides a better test of vestibular funtion as long as erebellar and proprioeptive funtions are intat. The subjet is asked to start with feet in the tandem position and arms folded against the hest and to make 10 steps at a omfortable speed. Most normal subjets an make a minimum of 10 aurate tandem steps in three trials. SECTION 3 Vestibular testing Eletronystagmography (ENG) Although a good examination of eye movements an be made by diret observation, reording tehniques inluding ENG, video-oulography, and spiral oil reordings allow a more detailed evaluation and provide a permanent reord for omparative purposes. ENG is the simplest and most readily available system for reording eye movements. An eletrode plaed laterally to the eye beomes more positive when the eye rotates towards it and more negative when it rotates away. The voltage hange represents the hange in eye position as only small angular movements are involved in nystagmus and the relation between voltage hange and eye movement is virtually linear at the small degrees of ar. The polarity of the reording is arranged so that a defletion of the eye to the left auses a downward defletion of the pen and a defletion of the eye to the right auses an upwards defletion. The sensitivity of the ENG an onsistently reord eye rotations of 0.5. This R L 30 L a a b b NEUROLOGY IN PRACTICE Figure 8 Internulear ophthalmoplegia (INO). The upper trae shows the movements of the right eye and the lower trae shows those of the left. At point a/a9 the eyes are looking straight ahead; at b/b9 the eyes are looking out at 30 to the left; at /9 the eyes are again looking straight ahead; at d/d9 the eyes are looking out at 30 to the right. The trae identifies a left INO with failure of the left eye to addut (d9) and nystagmus in the abduting right eye (d). d d

10 NEUROLOGY IN PRACTICE Standard protool for ENG testing with rotary hair Calibration eyes entred, eyes right at 30, eyes reentred, eyes left 30 (repeat) Gaze testing to haraterise nystagmus: (1) entre gaze, eyes open, then in dark for 20 s (that is, opti fixation inhibited) (2) gaze held at 30 to the right for 10 s, then 20 s in the dark (3) gaze held at 30 to the left for 10 s, then 20 s in the dark (4) if vertial nystagmus identified vertial eye movement reordings required with: (i) gaze upwards at 30 for 10 s, then 20 s in the dark; (ii) gaze down 30 for 10 s, then 20 s in the dark Visual stimuli (*using laser target for 1, 2 and 3) (1) Saades between two targets at 5 30 apart (2) Separate eye saades reordings taken from eah of the two eyes, paper speed 106 normal, then follow protool for gaze testing as above (3) Smooth pursuit at 0.1, 0.2, 0.3, 0.4 Hz, maximum veloity 40 /s (4) OKN full field, onstant veloity around vertial entral axis, at 40 /s, reverse diretion after 9 s Rotary hair testing (1) Impulsive rotational testing aeleration rise time of, 1 s to a onstant veloity of 60 /s (2) Sinusoidal VOR testing at 0.1, 0.2, 0.3, 0.4 Hz, maximum veloity 40 /s (3) VOR suppression at 0.1, 0.2, 0.3, 0.4 Hz, maximum veloity 40 /s *The advantage of a laser target is that its size remains onstant with distane from its soure, unlike onventional light soures, and an infinite number of omputerised projetion paradigms are possible for different test and researh purposes sensitivity is less than that of diret visual inspetion whih is approximately 0.1. The plane of the reording eletrodes defines the plane of reorded eye movement that is, eletrodes attahed medially and laterally to the eye will reord the horizontal omponents of eye movement, whereas those attahed above and below will reord vertial omponents. A single hannel ENG mahine summates the horizontal movements of both eyes from bitemporal reordings onto the same trae. The two hannel ENG mahine an reord the movement of eah eye separately (fig 8), and with four hannel use the tehnique an simultaneously reord the vertial movements of eah eye as well as the horizontal movements. The paper speed of 10 mm/s is used although when saadi auray and veloity are being tested, 100 mm/s or even faster may be neessary. Calibration is performed, so that a standard angle of eye deviation is represented by a known amplitude of pen defletion. Commonly the alibration is adjusted to obtain 10 mm of pen defletion per 10. Clinial relevane of ENG The main advantage of ENG reordings is that some patients demonstrate nystagmus that is only identifiable when opti fixation is removed. Peripheral vestibular disorders unless aute, these defiits are unlikely to be assoiated with nystagmus in the presene of opti fixation but an reveal nystagmus of inreased amplitude in darkness. The nystagmus is unidiretional with the largest amplitude on horizontal gaze towards the diretion of the fast omponent Vestibular nulei lesions in darkness the amplitude of the nystagmus may hardly alter but the veloity of the slow phase may be dereased. Often the nystagmus is bidiretional Cerebellar lesions these may be assoiated with pathologial square waves with duration of less than 200 ms. With diret urrent ENG reordings a harateristi abnormality of erebellar pathology is the failure to maintain lateral gaze in darkness with a slow drifting movement of the eyes. Rebound nystagmus an also be seen, but when erebellar, it is transitory and will persist for a maximum of 20 seonds. Patients with erebellar disease may also have diffiulties in exeuting ommands of saadi movements. When asked to turn their gaze laterally quikly they overshoot the target. Rotary hair testing allows measurement of the eye movement response to preise vestibular stimuli and an be of immense linial value. The VOR (vestibulo-oular reflex) provides a simple example of a reflex ar omprising the vestibular sense organ, the primary, seondary, and tertiary vestibular neurones and the effetor organ, the oulomotor musle. Angular aeleration in the plane of the semiirular anal leads to endolymph displaement in a diretion opposite to that of rotation and in onsequene the upula of that anal deviates in the same diretion as the endolymph, resulting in a hange of vestibular tonus, an exitatory stimulus being mathed by an inhibitory stimulus from the opposite side. As a result there is an impat on the pair of musles produing the ompensatory eye movement that is, exitation of the antagonist musle and disinhibition of the agonist musle. An aeleration to the right in the plane of the horizontal anal will produe deviation of the eyes to the left. VORs at during all natural head movements in life with oordination with visual and ervio-oular reflexes to provide the most appropriate eye position and eye stability during head movements. Vision has a powerful suppressive effet on vestibular nystagmus that an, however, be seen using Frenzel s glasses or VOG. Types of rotary hair stimuli Impulsive (step veloity) stimuli Constant veloities suh as 40, 60, 80 or 120 /s are attained with an abrupt aeleration of the hair, brought to onstant veloity within 1 seond. This onstant veloity is maintained for up to 2 minutes while the nystagmi response dies away. The hair is suddenly brought to rest with the same deeleration and the normal limits of nystagmus intensity are established with normal subjets. It provides a rapid assessment of gain (peak slow omponent veloity 4 hange in hair veloity) and the time onstant (time for the slow omponent veloity to fall to 37% of its initial value) of the anal reflex. Sinusoidal stimuli To and fro swinging movements of the hair around its vertial axis are programmed with variable stimulus parameters that is, frequeny and amplitude. The threshold for reordable nystagmus, defined as the angular aeleration maintained for 20 seonds that will produe nystagmus, is 0.15 /s 2 in the absene of opti fixation. With opti fixation the nystagmus threshold is raised and is normally about 1 /s 2. With iv41

11 iv42 omputer software analysis, sinusoidal VOR at different frequenies an be used to alulate gain and phase of the peripheral vestibular response. Rotational testing is normally performed in darkness but sinusoidal rotation an also be performed with the eyes foused on a target that revolves with the patient, around the vertial axis. This has the purpose of allowing VOR suppression to be assessed. This is an important test of entral vestibular funtion, as visual suppression of the VOR is mediated by entral vestibular pathways. Clinial relevane of rotary hair testing Rotational stimuli an be used to demonstrate a diretional preponderane as determined by the ratio of the duration of nystagmus following the onset of aeleration to that following deeleration. A disadvantage is that both labyrinths are tested simultaneously and a unilateral dysfuntion may be diffiult to identify if the lesion is old and the patient is well ompensated. It is of partiular value in the following situations: A negative alori test, where high frequeny osillation/ high intensity aeleration may give evidene of some residual vestibular funtion Investigation of visuo-vestibular interations: failure to suppress the vestibulo-oular reflex with fixation is evidene of entral vestibular dysfuntion. With omputerised analysis of responses to rotary hair testing, results an be depited in a quadranti fashion following the sequene of start/stop stimuli in a lokwise then antilokwise diretion. These displays inlude a mathematial omputation of diretional preponderane using slow phase veloity and/or durational riteria (vide infra). Dimitri et al 3 applied multivariate lassifiation tehniques of sinusoidal harmoni aelerations and measured asymtoti gain and the time onstant, and were able to demonstrate a minimal mislassifiation rate of 3.4% when omparing 57 normal with 30 patients with peripheral vestibular defiits that is, as defined by a total anal paresis on alori testing. Video-oulography This is a tehnique for observing eye movements whereby an infra-red amera is mounted within goggles and onneted to a video monitor. Observation and reordings of the eye movements in the absene of opti fixation an be made in response to a variety of stimuli and this tehnique is now a standard investigative tool in many audiology departments. A test protool an be performed whih allows videomonitoring of the following: spontaneous nystagmus head shaking nystagmus passive head tilt rotation of 180 body rotation with respet to head. As a tehnique for bedside vestibular testing, Vitte et al 4 learly demonstrated the value of VOG for identifying and lassifying peripheral vestibular lesions. Calori testing This is the most widely available of all the vestibular tests, and for many otologists is the ornerstone of vestibular diagnosis. Its great value is that it allows eah labyrinth to be tested separately. The stimulus is easy to apply and involves NEUROLOGY IN PRACTICE inexpensive methodology. The test remains unrivalled as a method of demonstrating a peripheral vestibular defiit. Priniples of alori testing After irrigation of the ear with water 7 C below (30 C), and then 7 C above (44 C) body temperature, a gradient is set up between the EAM and the two limbs of the horizontal anal. This is by virtue of the position of the patient, who is relined on the ouh and whose head is at 30 to the horizontal. This means that the horizontal semiirular anal beomes vertial and the temperature gradient rosses from one side of the anal to the other. It is believed that the endolymph irulates beause of the differene in the speifi gravity on the two sides of the anal. With warm water, there is ampullo-petal flow, with upular defletion towards the utrile, resulting in ativation of the VOR, a sensation of vertigo and horizontal nystagmus direted towards the stimulated ear. There are some questions regarding this onvetion theory, beause alori nystagmus still ours in spae under miro-gravity onditions. The Hallpike-Fitzgerald bithermal alori test has been available to liniians for more than 60 years. Eah ear is irrigated in turn for 40 seonds with first 30 C, and then 44 C water. Inspetion of the tympani membrane after warm irrigation onfirms an adequate stimulus if a red flush is seen on the tympani membrane. Diret observation of the eyes allows the end point of the nystagmi reation to be measured. During the proedure, the patient is asked to diret his gaze on a fixation point on the eiling above his head, making the end point easier to determine. At this point the lights are swithed off and the eyes observed with Frenzel glasses or infra red gun and under normal situations the vestibular nystagmus would be expeted to reappear. The end points of eah test are graphially reorded. Quantitative analysis Normally, nystagmus eases between seonds after onset of irrigation and will return for up to a further 60 seonds after the removal of opti fixation. Two harateristi patterns of response may appear, either separately or in ombination. (1) A total anal paresis is the omplete loss of labyrinthine funtion in one ear. This is seen when there is a total absene of nystagmus following both 30 C and 44 C irrigations, even in the absene of opti fixation. Ideally, the test should be repeated using old water at 20 for 60 seonds to onfirm the result. It may reflet an ipsilateral lesion of the labyrinth, the VIIIth nerve, or the vestibular nulei within the brainstem. (2) A diretional preponderane ours when the responses to thermal irrigations produe an exess of nystagmus in one diretion that is, towards either the right or the left. It indiates an imbalane of vestibular tone arriving at the oulomotor nulei and may result from peripheral vestibular lesions (that is, the labyrinth, the VIIIth nerve or the nulei) or from entral vestibular lesions (that is, within the erebellum or brainstem). With more pronouned degrees of vestibular tone imbalane, spontaneous nystagmus makes its appearane. Figures for duration of nystagmi responses in seonds an be entered into the Jongkees formula, whih allows

12 NEUROLOGY IN PRACTICE alulation of a perentage figure expressing the degree of anal paresis or diretional preponderane: The opti fixation index (OFI) is alulated by dividing the summed durations in the light by the summed durations in the dark. If there is no enhanement in the absene of opti fixation that is, the OFI is 1.0 the ause may be entral that is, in the erebellum or the vestibulo-erebellar trats. Bilateral dereased alori responses may indiate bilateral vestibular impairment, or may be the result of vestibular habituation for example, in professional arobats, ie skaters, and ballet daners (OFI, 0.5). ENG alori reordings There are both advantages and disadvantages assoiated with the use of ENG alori testing. It provides a permanent reord of the alori response in both light and dark, and allows individual features of the nystagmus that is, slow omponent veloity, inter-beat frequeny, and the amplitude to be analysed and a permanent reord kept (fig 9). The omparative disadvantages when ompared with the Fitzgerald-Hallpike tehnique are that: it is diffiult to detet the end point of the nystagmus as well as an be done with the naked eye reording the alori nystagmus with the eyes losed is ompromised by Bell s phenomenon other nystagmi omponents in the vertial diretion are missed that is, torsional nystagmus whih may give additional diagnosti information. A diret omparison has been made between the maximum slow omponent veloity and the durations of the four alori responses in 25 normal subjets. The durations were relatively stable as a parameter, whereas the slow omponent veloities showed onsiderable variations in some subjets. Further analysis showed that the test/re-test unreliability of the slow omponent veloity was unaeptably high. Diret visual observation has the advantage that the end point of the nystagmus an be estimated more reliably both with and without opti fixation, but does rely on an experiened observer. Closed iruit and air alori testing Some ommerial systems allow warming and ooling of the EAM with losed irrigation systems and alternatively with the use of air. The problem with the former is that the tube in whih the water is flowing does not fully oupy the EAM, thus reduing the effetiveness of the stimulus; and with the latter, the speifi heat of air is muh lower than that of water, whih means a greater temperature differential is required to effet the same temperature gradient aross the labyrinth that is, a hot air stimulus of 50 C whih needs to be delivered for 60 seonds will give an equivalent to the 44 C water stimulus, but may be poorly tolerated by patients. Calori testing is an essential part of the evaluation of the dizzy patient. It tests both labyrinths individually and does not require sophistiated instrumentation if water irrigations are to be used. The quantifiation and normal values of the measured parameters of the alori indued nystagmus have been well established. The Jongkees formula is a validated measure to alulate both anal paresis and diretional preponderane. iv43 Figure 9 Four quadrant display of alori irrigations showing a graphi reord of a set of normal responses to alori irrigation in the upper four quadrant display, with the lower four quadrant display showing a partial anal paresis on the left. From Toennies Computer- Assisted Diagnosti Systems, with permission of Professor John Allum, Basel, Switzerland, and Jaeger Toennies, Wurzburg, Germany. Posturography It is well established that alterations in vestibular funtion may profoundly affet posture. Postural ontrol is a vital physiologial funtion if we are to ontinue any of our daily ativities, and is determined by a omplex sensory motor feedbak system dependent on a variety of oordinated reflexes. Only in the last ouple of deades have objetive measures of vestibulo-spinal postural reflexes been possible. Clinially the Romberg s test has been used to assess postural stability. During normal standing, the body is in ontinuous motion that is, physiologial sway even when attempting to remain still. This is an ative proess, whereby any loss of balane is ompensated by movement of the

13 iv44 Figure 10 The Equitest balane platform allowing sway referening of both the support surfae and the visual surround. Reprodued with permission from NeuroCom International In, USA. body s entre of gravity. These movements result in visually detetable sway movements that maintain the body s entre of gravity vertially over the base of support. Stati fore plate posturography was an early method of measuring body sway. A typial fore plate onsists of a flat rigid surfae supported on three or more points by independent fore measuring devies. As the patient stands on the fourth plate, the vertial fores reorded by the measuring devies are used to alulate the position of the entre of the vertial fores exerted on the fore plate over time. With the height and weight of the patient, a omputer model of body dynamis an be used to derive the entre of gravity sway angle over time. Moving platform posturography has been designed to overome the limitations of the stati fore platform by ontrolling the relative ontributions of visual, somatosensory, and vestibular input. Commerially available platforms alulate body sway based on hanges in horizontally (sheer) and vertially oriented (torque) strain gauges mounted under the support surfae. The Equitest platform (fig 10) utilises the onept of sway referening that is, both the support surfae and the visual surround an be modulated in phase with the patient s own body sway. This oupling of either the platform or visual surround to the sway of the subjet allows: the angle between the foot and the lower leg to be maintained at a onstant value (minimising somatosensory input) NEUROLOGY IN PRACTICE the visual input to remain onstant despite the subjet s sway. Six onditions are used in the sensory organisation testing and analysis of the sway sores allows eah of the three priniple balane sensors to be isolated and omparisons made to assess the sensory preferene of the individual. With the moving platform, posturography has been shown to be of great benefit in rehabilitation but limited as a diagnosti test with a sensitivity of only 50%. 5 The sensory organisation test battery identifies abnormal patterns of postural ontrol, not adequately assessed by studies of the vestibulo-oular reflex alone, and examines the utilisation and integration of visual and somatosensory input with vestibular information, espeially under onditions of sensory onflit. Limitations of vestibular tests A major disadvantage of all types of vestibular test is that normative data are not universal and therefore eah dataset needs to be olleted for eah laboratory before it an be used for linial diagnosis. The equipment for the rotary hair and posturography is expensive and requires spae and dark rooms. There is no gold standard for vestibular testing and the results of all the tests in the battery must be used in onjuntion to develop the diagnosis. REFERENCES 1 Drahman DA, Hart CW. An approah to the dizzy patient. Neurology 1972;22: Baloh RW, Yee RD, Honrubia V, et al. A omparison of the dynamis of horizontal and vertial smooth persuit in normal human subjets. Aviation Spae Environ Med 1988;59: Dimitri PS, Wall C, Oas JG. Classifiation of human rotation test results using parametri modelling and multivariate statistis. Ata Otolarygnol Stokh 1996;116: Vitte E, Semont A, Freyss G, et al. Videonystagmosopy: its use in the linial vestibular laboratory. Ata Oto Laryngol Suppl 1995;520(II): Di Fabio RP. Meta-analysis of the sensitivity and speifiity of platform posturography. Arh Otoloaryngol Head Nek Surg 1996;122: Baloh RW, Halmagyi GM, eds. Disorders of the vestibular system. New York: Oxford University Press, A linial orientation to understanding vestibular disorders. 7 Baloh RW, Honrubia V, eds. Clinial neurophysiology of the vestibular system, 3rd ed. Philadelphia: Davis, An exellent text for understanding the basi vestibular sienes. 8 Brandt T. Vertigo: its multisensory syndromes, 2nd ed. London: Springer Verlag, A very thorough liniian s approah to vertigo. 9 Furman JM, Cass SP. Vestibular disorders: a ase-study approah, 2nd ed. New York: Oxford University Press, A very basi approah to the history, examination and findings of patients with vestibular disorders. 10 Leigh RJ, Zee DS. The neurology of eye movements, 2nd ed. Philadelphia: FA Davis, Exellent text regarding understanding of the physiology of eye movements. 11 Luxon LM. Textbook of audiologial mediine. London: Martin Dunitz, A omprehensive textbook, for use as a neuro-otologial referene. 12 Rudge P. Clinial neuro-otology. Edinburgh: Churhill Livingstone, A thorough neurology approah to the speialty of neuro-otology. 13 Kerr AG. Sott-Brown s otolaryngology Vol I-VI, 6 ed. Oxford: Butterworths, ENT textbook with further details of assessment tehniques mentioned in hapter.