Visual Suppression Of Caloric Nystagmus Research Articles

カルバマゼピン中毒により下眼瞼向き眼振を認めた薬剤性めまい症例

We report the case of a 33-year-old man who presented with disequilibrium and downbeat nystagmus. Balance testing showed failure of visual suppression of caloric nystagmus with insufficient optokinetic nystagmus responses, suggesting central vestibular dysfunction. However, MRI showed no lesions in the brain, including in the cerebellum. The patient had been diagnosed previously as having epilepsy, and the convulsions had remained under control for more than 10 years with a maintenance dose of carbamazepine (900mg/day). Blood tests revealed a serum level of carbamazepine of 10.7mEq/l, which was over the therapeutic range (4.0-10.0mEq/l). Therefore, his carbamazepine dose was reduced, and with a reduction of the dose to 600mg/day, his disequilibrium and downbeat nystagmus gradually disappeared, along with a decrease in return of the serum level of carbamazepine to the therapeutic range. Therefore, we diagnosed the disequilibrium with downbeat nystagmus in this patient as having been caused by carbamazepine intoxication. Although carbamazepine is metabolized by CYP3A4 in the liver, elevated levels of the drug have been reported in cases of renal failure. As he also suffered from polycystic kidneys, we consider that the progressive renal dysfunction in our patient could have precipitated the carbamazepine intoxication.

頭位性めまいを主訴とした脊髄小脳失調症6型 (SCA6) 例の ENG 検討

A 57-year-old woman presented at our outpatient clinic with the recent and frequent experience of paroxysmal positional vertical vertigo similar to the sensation of a somersault, especially changing position from sitting to lying supine, accompanied with spells of nausea and blackout. On examination, we observed prominent downbeat nystagmus in the primary eye position and lateral gaze. MRI disclosed prominent cerebellar cortical atrophy, especially in the vermal regions. The patient had a family history of spinocerebellar ataxia type 6 (SCA6) and had herself received a definitive diagnosis of the same phenotype disease from genetic studies. The points of the ENG findings were as follows: (1) downbeat nystagmus was prominent in the primary eye position and was combined with gaze nystagmus in the lateral gaze; (2) both horizontal & vertical rebound nystagmus were noted; and (3) impairment of both horizontal & vertical smooth pursuit were seen. In horizontal and upward pursuit, catch-up saccades (lower gain) were intermingled. In contrast, backup-saccades (higher gain) were intermingled in downward pursuit. Furthermore, (4) Horizontal saccades were hypometric, though vertical saccades were hypermetric (overshoot); (5) In both horizontal and vertical OKN, the slow phase of OKN was severely impaired. Finally, (6) vestibular caloric nystagmus was well induced bilaterally. Both sides of visual suppression of caloric nystagmus were severely impaired. Most of present results are well explainable with the pure cerebellar cortical atrophy as the typical pathological finding of SCA6. However, two important findings should be mainly discussed and stressed here. One, the gain of the horizontal smooth pursuit was lower, while the gain of the downward pursuit was higher. It seemed to be inconsistent that a single part of the cerebellum would simultaneously modulate decreasing gain of the horizontal and increasing gain of vertical smooth pursuit systems. Therefore, this finding suggested that several parts, not a single part, of the cerebellum would be simultaneously engaged in the gain modulation of the smooth pursuit system. Second, the severe impairments of both horizontal and vertical OKN implied disturbances of both the pursuit and the velocity storage systems. In Cohen & Raphan's model, the slow phase of OKN is composed of the “direct pathway” and the “indirect pathway.” The “direct pathway” utilizes the ocular pursuit system in the flocculus/paraflocculus, while the “indirect pathway” is mediated through the velocity storage system in the medial vestibular nuclei/prepositus hypoglossi nuclei or the interstitial nuclei of Cajal in the brainstem. Consequently, the present results of OKN strongly suggested that the neural circuits related to the velocity storage integrator in the brainstem would also be perturbed, together with the disturbance of the ocular pursuit system in the cerebellum.

VGCC antibody-positive paraneoplastic cerebellar degeneration presenting with positioning vertigo

A 70-year-old woman developed paraneoplastic cerebellar degeneration (PCD) due to P/Q-type and N-type voltage-gated calcium channel antibodies and small cell lung cancer, the main clinical manifestations of which were severe positioning vertigo and vomiting. Loss of the visual suppression of caloric nystagmus, spontaneous downbeat nystagmus, periodic alternating nystagmus, and positioning vertigo in our patient most probably corresponds to the cerebellar flocculus/paraflocculus lesion caused by PCD.

Eye movement disorders in myotonic dystrophy type 1

Conclusions. No definite sign was found of central oculomotor system disorders being independent of saccadic slowing because (1) diminished maximum slow phase velocity of the optokinetic nystagmus (OKNspv) was closely related to saccadic slowing (p<0.01, r=0.59), (2) maximum frequency of optokinetic nystagmus (OKNfq) was normal, (3) visual suppression (VS) change was mild, and (4) the diminished maximum slow phase velocity of the caloric nystagmus (CNspv) seen in some patients is explained by both peripheral and central vestibular involvement. These findings support the extraocular muscle hypothesis. Objective. To assess whether eye movement disorders seen in patients with myotonic dystrophy type 1 (DM1) are caused by central oculomotor system involvement or extraocular muscle damage. Patients and methods. Oculomotor functions and their correlation with (CTG)n length were studied in 29 DM1 patients and 12 age-matched controls. Results. Values for saccadic velocity (p<0.005), maximum OKNspv (p<0.005), and maximum CNspv (p<0.01) in the patient group were markedly lower than in the control group. VS of caloric nystagmus in the patient group was slightly lower than that in the controls. No significant difference was found between the two groups in the maximum OKNfq. Patients with greater (CTG)n lengths had lower saccadic velocities (p<0.01, r=0.71).

Ｐａｒａｎｅｏｐｌａｓｔｉｃ Ｎｅｕｒｏｌｏｇｉｃ Ｓｙｎｄｒｏｍｅの２症例

We encountered two patients with paraneoplastic neurologic syndrome who visited our ENT clinic complaining of vertigo. The first patient was a 73-year-old woman who was admitted to our hospital because of dysequilibrium and dysarthria of subacute onset. Chest CT showed swelling of the mediastinal and right hilar lymphnodes. Pathological examination of the hilar lymphnodes taken by thoracotomy revealed small cell carcinoma of the lung. Brain CT and brain MRI were normal. Cytological study of the cerebrospinal fluid was class I. Paraneoplastic cerebellar degeneration was diagnosed. Neuro-otological examinations revealed: 1) gaze nystagmus on both right and left lateral gaze, 2) saccadic pursuit, 3) hypometric saccades, 4) diminished caloric nystagmus and 5) decreased visual suppression of caloric nystagmus. Treatment with plasmapheresis was successful to improve limb/truncal ataxia, dysarthria, and neuro-otological findings. The second patient was a 54-year-old woman who had had surgical treatment 3 years before for ovarian cancer. She visited our ENT clinic because of vigorous vertigo and diplopia of sudden onset. Neurological examinations revealed reduced deep tendon reflexes and neuro-otological examinations revealed: 1) bilateral abducens nerve palsy, 2) gaze nystagmus on both right and left lateral gaze, 3) saccadic pursuit, and 4) markedly diminished caloric nystagmus. Gynecological examinations revealed recurrent ovarian cancer. Brain CT and brain MRI were normal. Cytological study of the cerebrospinal fluid was class I. Paraneoplastic brainstem encephalitis was diagnosed. Steroid pulse therapy improved her subjective symptoms and neuro-otological findings. We emphasize that the early induction of plasmapheresis or steroid pulse therapy should be used to treat patients with paraneoplastic neurologic syndrome and that neuro-oto-logical examinations are indispensable for quantitatively assessing the effectiveness of these treatments.

Ｖｉｓｕａｌ ｓｕｐｐｒｅｓｓｉｏｎ ｔｅｓｔに及ぼす眼位の影響 正常者と脊髄小脳変性症患者における検討

Caloric tests were performed in 38 normal volunteers and 63 patients with spinocerebellar degeneration (SCD).1) Maximum slow phase velocity of caloric nystagmus in darkness (SPV-max), 2) visual suppression of caloric nystagmus (VS) and 3) tonic deviation of the eyes in darkness just before a light was put on for visual supression (D) were measured from electronystagmographic recordings. D was defined as positive when the eyes deviated to the side of cold water irrigation and negative when the eyes deviated to the opposite side.1. Normal and SCD groups showed almost the same SPVmax value.2. The SCD group showed a lower VS value than the norm-al group (p<0.005).3. The mean value of D was positive in the SCD group, i.e. the eyes deviated to the side of cold water irrigation. In the normal group, it was also positive, but deviation was smaller than in the SCD group (p<0.025).4. SCD patients with gaze nystagmus showed a lower VS value than patients wIthout gaze nystagmus (p<0.005).5. Some SCD patients without gaze nystagmus showed a low VS value (≤ 30%).All of these patients showed a high D value (≥ 14°).6. Although some normal subjects showed a high D value, they all showed a normal VS value.A large D could represent a poor VS in some of the SCD patients, because, aecording to Alexander's law : the slow phase velocity of vestibular nystagmus is less when the eyes are deviated to the side of the slow phase. The present study confirms that a low VS value definitely indicates impairment of the central vestibular system even if the eyes are deviated to the side of the slow phase.

Visually Induced Eye Movements in Wallenberg's Syndrome

Eighteen patients with Wallenberg's syndrome were investigated concerning visually induced eye movements. All results were analysed quantitatively using a computer. In 16 out of 18 patients, OKN slow-phase velocities were impaired, in the remaining 2 patients they were normal. Patients who showed impaired OKN were classified into two groups according to directional asymmetry of OKN impairment. In 7 out of the 16 patients, slow-phases toward the lesion side were predominantly impaired in contrast to the slow-phases toward the intact side (group A). In the remaining 9 patients, slow-phases toward the intact side were predominantly impaired (group B). The smooth pursuit showed the same asymmetry as the OKN slow-phase, except, in 4 patients who showed normal smooth pursuit. All patients showed reduced visual suppression of caloric nystagmus during the slow-phase of nystagmus toward the lesion side, except 3 patients who showed normal visual suppression in both directions. CT scan failed to detect either the brainstem or the cerebellar lesions in any cases, but MRI performed on the most recent cases demonstrated the infarctions clearly. These findings suggest that infarctions are localized in the medulla in the patients of group A, but extend to the cerebellum as well as to the medulla in patients of group B.

Ｓｕｐｅｒｉｏｒ ｏｂｌｉｑｕｅ ｍｙｏｋｙｍｉａ症例

A patient with superior oblique myokymia, a term introduced by Hoyt and Keane in 1970, is described. The lesion responsible for superior oblique myokymia is discussed on the basis of the results of Neurootological examinations and Magnetic Resonance Imaging (MRI).A 55-year old woman consulted Gife University Hospital on November 28, 1985, complaining of abnormal eye movements.Neurootological findings : Her left eye showed abnormal movements characterized by rapid (8-9 Hz), small amplitude, intorsional and vertical motility. These eye movements were seen best when she looked down and to the left. The diagnosis was superior oblique myokymia. Optokinetic nystagmus and visual suppression of caloric nystagmus were within normal limits.Neuroradiological findings : MRI showed a lesion, suspected of being an arterio-venous malformation, which extended from the right cerebellar peduncle to the flocculus.Ishikawa (1983) reported that the lesion responsible for superior oblique myokymia was the contralateral flocculus. MRI findings in our case supported his speculation. But the results of optokinetic nystagmus and visual suppression tests suggested that the function of the flocculus was not impaired. We speculate that the lesion did not affect the function of the flocculus or that it affected the part of the flocculus which was not related to optokinetic nystagmus and visual suppression of caloric nystagmus.

The influence of physostigmine on visual-vestibular interaction in hereditary ataxias.

Visual suppression of caloric nystagmus was studied in five patients with hereditary ataxia before and after administration of physostigmine. All patients had an initial abnormal ocular fixation index that improved after physostigmine was given. The data indicate that there is a partly reversible disturbance of visual-vestibular interaction in patients with hereditary ataxia, caused by an impairment of a central cholinergic mechanism.

Vestibulo-ocular reflex, optokinetic response and their interactions in the cerebellectomized cat.

The effects of total ablation of the cerebellum on eye movements were studied in alert adult cats. The normal cat could easily hold a steady eye position after a saccadic movement in the dark. The cerebellectomized animal could not: after a saccade the eye position shifted towards a more central position. Vision reduced this 'post-saccadic drift'. The sinusoidal vestibulo-ocular reflex (v.o.r.) was strongly affected by total cerebellectomy. In darkness the v.o.r. gain remained stable at high frequencies (0.5 and 1 Hz) but decreased markedly at lower frequencies to as low as 0.18 at 0.05 Hz. A phase advance (up to 65 degrees at 0.05 Hz) paralleled this gain depression. Velocity characteristics of optokinetic nystagmus (o.k.n.) and optokinetic after-nystagmus (o.k.a.n.) induced by constant-velocity full-field rotation of 60 deg/s amplitude and 60 s duration were studied. The features of o.k.n. (initial velocity, maximal velocity and time constant) were only mildly affected by cerebellectomy. On cessation of visual stimulation when the animal was plunged into darkness, the velocity of the eyes decreased progressively (o.k.a.n.). The time constant of o.k.a.n. was 12.5 s in the normal cat and 4.2 s in the cerebellectomized cat. Furthermore cerebellectomy abolished the secondary o.k.a.n. Optokinetic response was also tested by a set of sinusoidal (0.05-1 Hz; 3-20 degrees) full-field stimuli. The o.k.n. was not abolished but dramatically decreased, especially at higher frequencies. No response could be detected above 0.15 Hz. Visual suppression of inappropriate vestibulo-ocular reflex was still possible but was mildly impaired after cerebellectomy. Visual suppression could only be detected with stimuli below 0.25 Hz. Visual suppression of caloric nystagmus was studied in the normal cat. A clear dependence of the effectiveness of visual suppression on the velocity of the nystagmus was demonstrated. In the cerebellectomized cat, the visual suppression of caloric nystagmus was lost when tested on nystagmus velocities above 20 deg/s but remained when tested on nystagmus velocities below 20 deg/s. The relationship between cerebellectomy and the loss of visual suppression of caloric nystagmus was found to be at least partially indirect: cerebellectomy increased the velocity of caloric nystagmus, and visual suppression was usually less effective at higher velocities.

Role of the nucleus reticularis tegmenti pontis on visually induced eye movements

Optokinetic nystagmus (OKN) and visual suppression of caloric nystagmus were tested in cats with electrolytic lesions in the nucleus reticularis tegmenti pontis (NRT) or with hemicerebellectomies. The animals with a NRT lesion could follow higher stimulus velocities, but the eye movement output saturated at 10°/s. In the hemicerebellectomized cats, on the other hand, slow-phase OKN velocity was normal at stimulus velocities less than 30°/s. In addition, OKN impairment was more transient in the cats with hemicerebellectomies than in those with NRT lesions. In the cats with a NRT lesion, loss of visual suppression of caloric nystagmus was apparent in nystagmus with the slow phase toward the lesion side, whereas in cats with hemicerebellectomies, it was toward the contralateral side to the lesion. These findings suggest that the NRT may be a part of the relay nuclei mediating optokinetic signals responsible for OKN at all optokinetic stimulus velocities and the flocculus may be responsible for OKN at higher optokinetic stimulus velocities. In addition, the NRT may also be one of the prefloccular nuclei conveying visual input signals responsible for visual suppression of caloric nystagmus to the contralateral flocculus.

Slow Eye Movements in Patients with Neurological Disorders

Gain (eye velocity/stimulus velocity) of vestibular and optokinetic nystagmus, gain of smooth pursuit, and degree of visual suppression of caloric nystagmus were estimated in normal subjects and in patients with vestibular neuronitis, and disorders in frontal cortex, cerebellum or brain stem. It was found that the visual tests discriminated better between disorders of central origin than did the vestibular test. Visual suppression of caloric nystagmus was more frequently defective in patients with decreased gains of optokinetic nystagmus and smooth pursuit than in patients with normal results on visual tests.

頭頂葉障害と眼球運動

Thirty-three cases of unilateral parietal lobe lesions were studied. Eye movements were observed and recorded by electronystagmography (ENG). The lesions were confirmed neuroradiologically.1. Unilateral lesions in the superior part of the parietal lobe produce asymmetric optokinetic nystagmus and saccadic pursuit movements to the side of the lesion. This means a reduction in the slow phase of nystagmus to the side of the lesion. Therefore, the optokinetic nystagmus to the side of the lesion is better than that to the normal side. The visual suppression of caloric nystagmus is normal in these lesions.2. Unilateral lesions in the inferior part of the parietal lobe also produce asymmetric optokinetic nystagmus. The optokinetic nystagmus to the side of the lesion is better than that to the normal side; however, the optokinetic nystagmus to the side of the lesion itself showes poor response. The pursuit eye movements are saccadic on both sides. The quick eye movements to the normal side are impaired and those to the side of the lesion are normal or slightly impaired. The pursuit movements are bilaterally impaired and the pursuit movements to the side of the lesion are more strongly impaired than those to the normal side. Visual suppression is reduced or abolished bilaterally.

On the role of the nucleus reticularis tegmenti pontis for visual suppression of caloric nystagmus

Loss of visual suppression (VS) of caloric nystagmus was produced after creating flocculus destruction. The flocculus receives visual signals through a climbing fiber pathway and also through a mossy fiber pathway. In the previous report, we stated that the inferior olive as a source of the climbing fiber might be unrelated to the immediate modification of the vestibuloocular reflex by visual stimuli. A mossy fiber pathway presumably via the superior colliculus is a likely candidate for visual suppression of caloric nystagmus. A very recent anatomical and physiological experiment has revealed that the nucleus pontis (NP) and the nucleus reticularis tegmenti pontis (NRT) project mossy fibers to the flocculus.In the present experiment, major concerns were to ascertain whether NP or NRT is the prefloccular relay nucleus responsible for the VS of caloric nystagmus. To achieve this goal, the VS of caloric nystagmus and optokinetic nystagmus (OKN) were investigated after making lesions in NP or NRT in 27 cats. After making the NP lesions, the VS of caloric nystagmus was revealed and OKN was normal in all the cats with the NP lesion. After making the NRT lesion, loss of VS was observed toward the side opposite to the lesion and OKN showed directional preponderence to the lesion site. These experimental findings are quite compatible with the fact that the early component of the field potentials in the flocculus induced by strobe flashes decreased markedly after making a lesion in the contralateral NRT. Together with the anatomical evidence that the superior colliculus sends its fibers to the NRT, the mossy fiber pathway via NRT is believed to be the final relay nuclei responsible for the VS of caloric nystagmus.

Visual suppression of caloric nystagmus and optokinetic responses in cats.

Previously it was reported that loss of visual suppression (VS) was accompanied by disturbance of optokinetic nystagmus (OKN) in monkeys with lesions at the flocculus. In the present experiment with cats, OKN was investigated after inflicting lesions on either superior colliculus (SC) or inferior olive (IO), both of which are considered to be the main prefloccular relay nuclei to mediate visual signals to the flocculus. VS of caloric nystagmus was recognized in all the IO-lesioned cats and OKN remained normal except in one cat. After the left SC lesions, loss of VS was evidently revealed and optokinetic stimuli produced directional preponderance to the left with diminished responses to the right in 7 of 9 cats. The present findings suggest that the SC may be an important relay nucleus to the flocculus in conveying visual signals responsible for VOR gain.

Cerebral Contribution to the Visual Suppression of Vestibular Nystagmus

Thirty-two patients with cerebral lesions were examined to locate cerebral areas involved in visual suppression. Visual suppression was reduced or abolished when the lesions were in the parietal lobe, especially in the dorsoposterior region. This part of the parietal lobe seems to modify visual suppression of caloric nystagmus that is mediated by the flocculus and nodulus of the cerebellum as well as the pons. In patients with frontal lobe lesions including the parietal lobe, visual suppression was reduced or abolished. Thus, the parietal lobe is important for this visual suppression mechanism.

Loss of visual suppression of caloric nystagmus in cats.

Loss of visual suppression (VS) of caloric nystagmus was produced after creating flocculus lesions. The flocculus receives visual signals through a climbing fiber pathway via the inferior olive (IO) and through a mossy fiber pathway (MF) presumably via the superior colliculus (SC). In order to elucidate the prefloccular nuclei responsible for VS of caloric nystagmus, VS of caloric nystagmus was investigated after making lesions in such nuclei as the SC and the IO in 42 cats. After the IO lesion, VS of caloric nystagmus was revealed in all IO-lesioned cats throughout the whole experimental course. After the SC lesion, loss of VS was constantly observed and persisted in 7 out of 9 cats. Hence, the MF pathway via the SC is believed to be the most likely candidate for the immediate modification of the vestibuloocular reflex by visual stimuli.

Immediate Modification of Vestibulilo-ocular Reflex by Visual Stimuli

Loss of visual suppression (VS) of caloric nystagmus was produced after creating flocculus lesions. The flocculus receives visual signals through a climbing fiber pathway via the inferior olive (IO) and through a mossy fiber pathway (MF) presumably via the superior colliculus (SC). In order to elucidate the prefloccular nuclei responsible for VS of caloric nystagmus, VS of caloric nystagmus was investigated after making lesions in such nuclei as the SC and the IO in 42 cats under halothane or α-chloralose with pentobarbital sodium anesthesia. After the IO lesion, VS of caloric nystagmus was revealed in all IO-lesioned cats throughout the whole experimental course. After the SC lesion, loss of VS was constantly observed and persisted in 7 out of 9 cats. Hence, the MF pathway via the SC is considered to be the most likely candidate for the immediate modification of the vestibulo-ocular reflex by visual stimuli.

The Relationship between Loss of Visual Suppression of Caloric Nystagmus and Optokinetic Nystagmus

The gain control of the flocculus is executed with the aid of oculomotor function toward the direction of improving the stabilization of the retinal images during head movements. Visual suppression (VS) of caloric nystagmus occurs also in the direction of stabilizing retinal images of visual surroundings. In fact, VS of caloric nystagmus is lost after total destruction of the flocculus. Under such conditions, optokinetic nystagmus involving smooth pursuit of eye movements and fixation may also be disturbed. In the present experiment using cats, the optokinetic nystagrxmus was investigated after lesions had been induced in the superior colliculus (SC) or the inferior olive (IO), both considered to mediate visual signal to the flocculus. VS of caloric nystagmus, and optokinetic nystagmus remained normal in all IO-lesioned cats. After the SC lesion, loss of VS was always evident, and optokinetic stimuli produced directional preponderance to the left and diminished response to the right in 7 of 9 cats. Hence, the SC is considered to be the one of the main relay nuclei in the mediation of visual signals responsible for the immediate modification of VOR by visual stimuli.

Visual Suppression of Caloric Nystagmus in Cats

A newly devised animal box with which caloric tests can be easily performed in the awake cat is presented. This device is also useful for position and optokinetic tests. Visual suppression of caloric nystagmus was investigated in such vertebrates as monkeys, cats and rabbits. There was a definite species difference in the rate of visual suppression of caloric nystagmus. It may be that the difference among species is due to a difference in fixation function among animal species.