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Case of downbeat nystagmus influenced by otolith stimulation.

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1954
Case of Downbeat
Nystagmus Influenced
by Otolith Stimulation
B. R. Chambers, FRACP, J. J. Ell, FRACP,
and M. A. Gresty, P h D
A patient with downbeat nystagmus and familial ataxia
is described. The nystagmus was induced by static tilt
away from normal upright posture, by linear acceleration of the head, and by convergence. It is inferred that
the nystagmus was modulated by otolith-specific stimuli
and not by stimulation of the canals. These findings
demonstrate the role of otolith function in generation of
eye movements in the vertical plane and support proposed interrelationships between otolith and vergence
mechanisms. The nystagmus and associated oscillopsia
were partially suppressed by treatment with clonazePam.
Chambers BR, Ell JJ, Gresty MA: Case of
downbeat nystagmus influenced by otolith stimulation.
A n n N e u r o l 13:204-207, 1983
Downbeat nystagmus (DBN) is an abnormality of ocular movement, usually vestibular in type, and frequently attributable to an intraaxial lesion at the level
of the foramen magnum [41. Associated abnormalities
predominantly include the Arnold-Chiari malformation, cerebellar and brainstem degeneration, and primary demyelination { 31. The mechanisms postulated
for DBN suppose that it reflects imbalance of tonic
vestibular control in the vertical canal system [l] or,
alternatively, that it results from defective smooth pursuit mechanisms in the vertical plane {lo].
This report describes D B N in a patient with a familial degenerative disorder, in whom the nystagmus was
provoked by static tilt and by linear acceleration of the
head in the apparent absence of canal influences. This
finding has important implications for the possible
mechanism of some cases of DBN and the presumed
role of otolith function in the generation of vertical eye
movement.
Case Report
A 61-year-old woman was referred for evaluation of D B N .
From 1971 until 1978 she experienced six episodes of
vertigo and nausea exacerbated by postural change. All ex-
From the Medical Research Council, Neuro-Otology Unit, Institute
of Neurology, National Hospital, Queen Square, London, England.
Received Mar 18, 1982, and in revised form May 13. Accepted for
publication May 16, 1982.
Address reprint requests to Dr Gresty, MRC Neuro-Otology Unit,
National Hospital, Queen Square, London W C l N 3BG, England.
204 0364-5 134/83/020204-04$1.50 0 1 9 8 2 by t h e American Neurological Association
cept one episode followed long airplane flights, after which
the symptoms persisted for one o r two days. The other episode followed a bout of influenza. Since 1977 she had been
increasingly aware of oscillopsia in the vertical plane not associated with vertigo or nausea. The oscillopsia was particularly
marked with head positions other than upright, and especially
with the head back and turned to the side. For the last two
years her sister, aged 65, had also experienced oscillopsia in
the vertical plane and was found to have D B N . The patient
had had a son who died at 12 months of age from Tay-Sach's
disease.
O n examination no nystagmus was present in the primary
position of gaze, but convergence evoked brisk D B N . D B N
was evident on both lateral gaze and downward gaze and was
accentuated in these positions by convergence. When the
patient viewed a distant target with her eyes in the primary
position, movement of the head to any position o(her than
upright provoked nonfatiguing D B N without a latent period.
The nystagmus obeyed Alexander's law, i.e., the slow phase
velocity was proportional to the displacement of the eyes in
the downward direction. Following movements were impaired in the horizontal plane, and more so in the vertical
plane, while saccadic eye movements were normal. Doll'shead eye movements were intact, and manual shaking of the
head and shoulders, which induced head movements in vertical and horizontal planes, did not significantly degrade visual
acuity. Failure of vestibuloocular reflex (VOR) suppression
was noted in all planes. Ocular counterrolling reflexes were
present. With the eyes open her gait was steady, but when
walking with eyes closed, she veered to the left. With the
Romberg test she fell backward and to the left. The remainder of the neurological and general examination was normal.
Fig 1. The influence of static tilt on downbeat nystagmus. At the
beginning of each trace the patient was seated zn novmal upright
position with respect to gravity, indicated by the + I g letiel. Progressive downward tilt of the right ear t o a horizontal position
(Od induces the nystagmus. W i t h return to normal vertical position the nystagmtls decreases in a m p h d e . Recordings were taken
in darkness.
Pure-tone audiometry revealed mild symmetrical, midfrequency sensorineural hearing loss bilaterally. Bithermal
caloric testing produced prolonged nystagmus that was
poorly suppressed by fixation. Bitemporal Dc-coupled electrooculography (EOG) confirmed the clinical observations.
Nystagmus was accentuated in darkness. Responses to fullfield optokinetic stimulation in the horizontal plane were
normal and symmetrical. Impulsive angular acceleration
and deceleration in a Barany chair produced prolonged,
symmetrical nystagmus with a high-frequency VOR gain in
total darkness of 0.7. The details of further neurootological
tests examining the influence of static tilt and linear acceleration on D B N are presented in the following section.
Results of standard hematological and biochemical tests
were normal. Plain radiographs of the cervical spine and skull
showed mild degenerative changes. Metrizamide myelography and computerized tomographic cisternography showed
no structural abnormality at the craniocervical junction. A
diagnosis was made of familial ataxia with DBN. The patient
was treated with clonazepam, 0.5 mg three times a day. When
reviewed two months later, the D B N was less evident and
her oscillopsia was no longer troublesome even when she was
supine.
Results of Neurootological Investigations
The effects of tilt and linear acceleration on the patient's D B N were investigated. The patient was subjected to static tilts in the planes of pitch (about a horizontal rotational axis moving in the sagittal plane) and
roll (about a horizontal axis moving in the coronal
plane), and to combinations of these movements, by
means of a biaxial gimbal capable of rotating about a
vertical and horizontal axis (Fig 1, inset). Observations
were made of the induced nystagmus using Dc-coupled
EoG and visual inspection. EoG
were
taken both in light and in complete darkness.
Deviation in all directions from normal upright posture induced DBN, the amplitude of which was proportional to the angle of tilt but unrelated to specific
UP
m
0
[
o
-
down
/
2
Og (horizontal)
Case Report: Chambers et al: Downbeat Nystagmus 205
forward
H
Control
direction. The nystagmus was most marked when the
patient was upside down. An example of nystagmus in
response to tilt in the coronal plane is presented in
Figure 1. The dynamic phases of tilt were executed
both quickly and as slowly as possible. If tilting was
done quickly, a small and transient exacerbation of the
nystagmus occurred that could be attributable to
semicircular canal activity. However, once angle of tilt
was attained, the nystagmus remained constant in slowphase velocity with no sign of decay during prolonged
periods of observation. Upon return of the patient to
upright posture, the nystagmus could persist for several
minutes as if there were an hysteresis. Although the
subject reported that the head back, left ear down position induced the strongest subjective sensations of disequilibrium (probably due to oscillopsia), tilt in this
plane did not induce a nystagmus of any greater amplitude.
The effects of linear acceleration on the DBN were
investigated using a lift (elevator) to produce accelerations in the vertical plane and a modified go-cart to
induce accelerations in the horizontal plane. The cart
was fitted with inflated bicycle tires and ran on a
smooth surface to minimize secondary angular motion.
The patient could be seated upright or reclined to the
supine position, and the head and trunk were supported to minimize angular movement (Fig 2, inset).
Recordings of eye movements were made using EOG,
and head acceleration was monitored with a DC piezoresistive accelerometer mounted on the forehead and
oriented with its sensitive axis in the direction of
motion.
With the head in normal upright posture, linear acceleration in any horizontal direction provoked nystagmus. This finding was in accord with the observation
from the tilt experiment that tilt in any direction from
upright induced nystagmus. When linear acceleration
was applied in the rostrocaudal axis of the skull (i.e., an
axis that would be normal to the plane of the utricular
macula) whether the head was prone or supine, DBN
was provoked with an amplitude that modulated with
the direction of acceleration. The results of the experiment are illustrated in Figure 2. Accelerations along
206 Annals of N e u r o l o g y Vol 13 No 2
February 1983
Fig 2. Effects of linear acceleration on positional downbeat nystagmus. The control records were obtained with the patient in the
supine position in darkness. The amplitude of the nystagmus was
modulated by application of an approximately trapezoidal acceleration in the indicated direction. (E = eye movement recordings;
H = head acceleration.)
the vertical axis toward the vertex of the skull abolished or reduced the amplitude of any nystagmus present. In this direction, acceleration is codirectional with
the force of earth’s gravity in normal upright posture.
Acceleration in a caudal direction from the vertex induced DBN. This corresponds to the subject being in
free fall or being tilted away from the upright posture.
Discussion
The DBN in this patient was provoked by static head
tilt and linear acceleration unrelated to the planes of
the canals and corresponding to the static and dynamic
components of otolith function [G, 7 ) . Angular accelerations of the head did not produce comparable modulation of nystagmus amplitude. The fact that linear accelerations produced complete amplitude modulation in
the absence of canal influences indicates that this particular case of D BN is attributable to derangement of
otolith-related functions, and not, as previously postulated C1, 101, to imbalance of canal function or defective smooth pursuit mechanisms. On the principle of
parsimony, it is sufficient to postulate a solely otolithrelated origin for the present case of DBN. The vestibular reflexes were intact in this patient and there
were other signs of central neurological disorder, so it
is unlikely that a peripheral lesion was responsible for
the nystagmus.
Physiological studies in normal human beings have
failed to demonstrate eye movements of great amplitude in response to linear acceleration in the planes
of utricular and saccular maculae IS}. By contrast, our
findings indicate that otolith stimulation can have a
strong influence on vertical eye movement. An explanation for this discrepancy may be found in geometrical
considerations relating to otolith-ocular reflexes that
have been neglected previously. Theoretically, the vertical otolith-ocular reflex should depend upon the distance between the target and observer, there being a
maximum compensatory eye movement when a near
object is being observed E2f. Thus, activation of vergence mechanisms should increase the gain of the
otolith-ocular reflex. In the patient described, convergence exacerbated the D B N if present and induced it if
absent. Our general experience is that convergence
may have a variable effect on DBN. The influence of
vergence on the gain of the otolith-ocular reflex may
explain some of those cases in which convergence enhances vertical nystagmus.
Positional nystagmus of the central type is a frequent
finding in a variety of neurological conditions. Clinical
and experimental studies have failed to delineate either
a mechanism or a precise anatomical localization of the
lesion. However, the experimental findings of Fernandez et al 151 are relevant and informative for the case
presented. Following extirpation of the cerebellar
nodulus in the cat, isolated postural D B N was observed that could be abolished by bilateral labyrinthectomy. If the labyrinthectomies were performed before
the nodulectomy, then D B N did not occur. Exactly
how nodulectomy induced DBN is not clear; removal
of inhibitory control over otolith-ocular reflexes is possible but has not been established. These experimental
findings suggest the possibility that our patient had a
lesion of the cerebellar nodulus and, since her sister
had a similar disorder, that it was genetically determined. It could be argued that if a nodulus lesion was
responsible for D BN in this patient, one might have
expected other signs of cerebellar dysfunction. However, the occurrence of D B N as an isolated sign has
previously been reported in two brothers in whom dysarthria, incoordination, and cerebellar ataxia developed
some years later {9}. Radiological investigations were
normal, and a genetically determined disorder was postulated.
The implication from the present study is that lesions affecting the otolith-ocular reflexes may in some
cases be important in the generation of nystagmus of
vestibular type in the vertical plane. This has not been
considered in previous hypotheses. By analogy to the
effects of nodulectomy in cats, it is possible that the
observation of D B N provoked or aggravated by postural change may be specific for nodular lesions.
We are grateful to Dr P. Rudge, who referred the patient for
investigation.
2. Barnes GR: Vestibular control of oculomotor and postural
mechanisms. Clin Phys Physiol Meas 1:3-40, 1980
3. Cogan DG: Downbeat nystagmus. Arch Ophthalmol 80:757768, 1968
4. De Jong JMB, Cohen B, Marsuo V, Vemura T: Midsagittal
pontornedullary brainstem section: effects on ocular adduction
and nystagmus. Exp Neurol 68:420-442, 1980
5 . Fernandez C, Alzate R, Lndsay JR: Experimental observations
on postural nystagmus. Ann Otol Rhino1 Laryngol 69:94-114,
1960
6. Lowenstein 0, Roberts TDM: The equilibrium function of the
otolith organs of the thornback ray. J Physiol (Lond) 110:392415, 1950
7. Lowenstein 0,Saunders RD: Otolith-controlled responses from
the first order neurons of the labyrinth of the builfrog to changes
in linear acceleration. Proc R SOCLond {Biol] 191:475-505,
1975
8. Niven JI, Hixson WC, Correia MJ: Elicitation of horizontal
nystagmus by periodic linear acceleration. Acta Otolaryngol
(Srockh) 62:429-441, 1966
9. Schotr GD: Familial cerebellar ataxia presenting with downbeat
nystagmus. J Med Genet 17:115-118, 1980
10. Zee DS, Friendlich AR, Robinson DA: The mechanism of
downbeat nystagmus. Arch Neurol 30:227-237, 1974
Neurological and
Neuroradiological
Examination of
Chronic Cannabis Smokers
Jan Hannerz, MD," and Thomas Hindmarsh, MDj
Twelve subjects, eight male and four female, who
had smoked on average more than 1 gm of cannabis
daily for 10 years, were investigated with a clinical
neurological examination and computed tomography
(CT) of the brain. No subject had a history of major
head trauma or cerebral infection, and just one abused
alcohol. Only the subject with a history of alcoholism
showed any abnormal cerebral function on clinical
tests or any abnormality in the CT scan, compared
with normal controls.
Hannerz J, Hindmarsh T: Neurological and
neuroradiological examination of chronic cannabis
smokers. Ann Neurol 13:207-210, 1983
Cannabis smoking has been reported to induce
chronic neurotoxic effects as well as structural
changes of the brain [61. In 1971, cerebral atrophy
Drs Chambers and Ell are supported by Alexander Piggott Wernher
Training Fellowships.
References
1. Baloh RW, SpoonerJW: Downbeat nyscagmus: a type of central
vestibular nystagmus. Neurology (NY) 31:304-3 10, 1981
From the Departments of "Neurology and J-Neuroradiology,
Karolinska Sjukhuset, S-104 01 Stockholm, Sweden.
Received Feb 17, 1982, and in revised form Apr 29. Accepted for
publication May 8, 1982.
Address reprint requests to Dr Hannerz.
0364-5 134/83/020207-04$1.50 0 1982 by the American Neurological Association
207
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