Journal of the New Zealand Medical Association, 19-September-2008, Vol 121 No 1282
Superior canal benign positional vertigo
The most common cause of vertigo is benign positional vertigo (BPV). Positionally-induced vertigo was recognised early in the 20th Century, but the clinical features of “classical” BPV were not described until 1952 by Dix and Hallpike,1 based on their provocative positional test. The patient is seated near the end of the examination couch, preferably wearing Fenzel glasses to magnify the eyes for the examiner.
The head is turned 45 degrees to one side and the patient tipped back with the head down. After a few seconds the patient experiences vertigo and has torsional geotropic (fast phase towards the ground) nystagmus seen when the eyes are directed towards the symptomatic side. The nystagmus and vertigo usually last less than 30 seconds. When the patient is sat up, the nystagmus direction reverses.
Dix and Hallpike suspected the disorder was caused by an abnormality of the otolith organs. With the advantage of high quality temporal bone histology Schuknecht2 thought that the nystagmus was explained by a posterior canal receptor made heavy, most likely by an otoconial particle which had become attached to it.
Early attempts at treatment were based on that assumption. Others, including Epley, made models and concluded that the “classical” signs were better explained by a particle loose in the posterior canal. A photograph of otoconia in a surgically opened posterior canal and the eventual acceptance that repositioning treatments work have confirmed the mechanism.3
In the early days of vestibular research (before video cameras) torsional nystagmus was difficult to record. Electronystagmographic recordings favoured nystagmus in the horizontal plane. However, it was by this technique that the first recordings of horizontal canal BPV were made.4 These confirmed Epley’s prediction that BPV could be caused by otoconia in any semicircular canal.5 Epley presented a chart showing the likely pattern of nystagmus for each type.
In the 1960s, experiments in cats had defined the unique three-neuron connection between canal receptors and the extraocular muscles.6 Each receptor is connected to one ipsilateral and one contralateral muscle. The second-order neurons are either excitatory (to the agonist muscles) or inhibitory (to the antagonist muscles). The connections for a posterior canal receptor and a superior canal receptor in a left ear are shown in Figure 1 and Figure 2.
In “classical” posterior canal BPV, a provocative positional test will cause an ampullo-fugal (excitatory) deflection of the posterior canal receptor resulting in a torsional apogeotropic (anatomically downward) deflection of the eyes, followed by their fast-phase return (geotropic or anatomically upward). If there were a particle in a superior canal, a similar ampullofugal receptor deflection could occur during a provocative positional test when the symptomatic ear is upper-most (Figure 2).
Figure 1. Left posterior canal benign positional vertigo. Left ear down
(IR=inferior rectus, SO=superior oblique, SR=superior rectus, IO=inferior oblique)
Figure 2. Left superior canal benign positional vertigo. Left ear up
(IO=inferior oblique, SR=superior rectus, SO=superior oblique, IR=inferior rectus)
A 51-year-old female had an approximately 10-year history of episodic positional vertigo lasting days which would occur twice a year. In 2000 it was confirmed as being “classical” left posterior canal BPV. In 2004 she presented after having awoken with postional vertigo. When sitting she had no nystagmus.
A Hallpike provocative positional test was performed (Figure 3). With the left ear down there was no response. With the right ear down, after 5 seconds, she experienced vertigo and there was a nystagmus whose fast phase was apogeotropic (anatomically downward), which ceased when she sat up. This implied BPV generated by a superior canal receptor, most likely in the opposite (left, upper) ear.
On that presumption two reverse (beginning with left ear up) Epley canalith repositioning procedure sequences7 were performed, after which no positional nystagmus could be elicited. She remained free of symptoms until approximately 6 months later when she presented with horizontal canal BPV in the same ear. This patient has now had all three types of BPV in one ear.
Figure 3. Video-clip. Hallpike positional test with right ear down and left ear up. Downbeat nystagmus with a latency of 5 seconds and a small torsional component
Vertical nystagmus, particularly downbeat, should alert the clinician to the possibility of central pathology. Caudal brainstem compression (e.g. Chiari malformation, hereditary spinocerebellar ataxia, and long-term lithium therapy) is in approximately half of the main causes. In the other half no cause is found.8
Until relatively recently it was assumed that positionally-induced nystagmus that was not "classical" BPV must have a central cause. The discovery of horizontal canal BPV explained most of the variations. In 1995, Epley’s elegant description of superior canal BPV was theoretical.
In 1994, Brandt9 had alluded to “...the rare anterior [superior] canal BPPV, the spontaneous symptoms occur when the affected ear is uppermost”. However, the first detailed cases are attributed to Susan Herdman10 who described two patients whose positionally-induced vertigo was accompanied by downbeat and torsional nystagmus likely to be caused by a superior canal receptor, and which ceased after repositioning treatment appropriate for BPV. Subsequently superior canal BPV has been recognised and reported by others10–15 in whose series it represents approximately 1% of all BPV diagnoses.
Bertholon et al13 reviewed 50 consecutive patients who had positionally-induced Nystagmus. In 75% there was a central cause (multiple system atrophy, cerebellar degeneration and other miscellaneous causes). In nearly all the downbeat nystagmus was triggered by the Hallpike test, and its onset was immediate.
In 25% (“idiopathic”) who presented with positional vertigo, the Hallpike test or a head-hanging test elicited vertigo and downbeat nystagmus with a short latency. In half the subjects a torsional component could be seen through Frenzel glasses, but in one it was only discernible by video-imaging. Aw et al15 studied forty-four consecutive patients who had not responded to conventional office repositioning treatments with 3-dimensional search coils in a 2-axis whole-body rotator. Seven had downbeat nystagmus with a torsional component assumed to indicate the symptomatic superior canal. All responded to a “head-over-heels” forward rotation in the plane of the identified canal.
Superior canal BPV is assumed to be rare because the posterior arm of the canal descends directly to the common crus, and debris within it should clear easily. For that reason, like horizontal canal BPV, it often resolves quickly with changes in head orientation likely to occur in everyday activities, or turning over in bed.
Differences in the orientation of the ampullary segments of the posterior and superior canals explain why (1) superior canal BPV can be elicited by a Hallpike test to either side, or to a head-hanging test, and (2) the smaller torsional component for superior canal BPV, which is predominantly downbeat.13,15
In summary, superior canal BPV is now recognised as rare form of BPV, observed in approximately 1% of large series. The presenting symptom is positional vertigo. As with all forms of BPV the patient must experience vertigo on a Hallpike positional test, which may be positive to either side, or on a head-hanging test.
The nystagmus has a short latency and is downbeat, with a torsional component which may be indiscernible to clinical observation. A past history of posterior or horizontal canal BPV supports the likelihood of superior canal BPV. Otherwise, in a patient with positionally-induced downbeat nystagmus, the absence of these features and non-response to respositioning treatment makes a central cause likely.
Author information: Jeremy Hornibrook, Otolaryngologist–Head & Neck Surgeon, Christchurch Hospital (and Adjunct Professor in the Department of Communication Disorders, University of Canterbury), Christchurch
Acknowledgment: I thank Professor GM Halmagyii (at the Royal Prince Alfred Hospital, Sydney) for verification of the observations and conclusions and for helpful comments.
Correspondence: Jeremy Hornibrook, Department of Otolaryngology-HNS, Christchurch Hospital, Private Bag 4710 Christchurch, New Zealand. Fax: +64 (0)3 364 0273; email email@example.com
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