Visual modulatory influences of vestibulo-ocular reflex in patients with vertigo.
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PURPOSE: Downbeat nystagmus (DBN) is a typical ocular motor sign in patients with lesions of the vestibulocerebellum. A vertical vestibular tone asymmetry, an upward shift of the eyes' null position for vertical gaze holding, or an imbalance of vertical smooth-pursuit signals have been proposed as mechanisms of DBN. The purpose of this study was to elaborate a possible link between an imbalance in the vertical smooth-pursuit system and DBN by relying on a healthy human model. METHODS: Healthy subjects (n=6) were exposed to continuous asymmetric smooth-pursuit stimulation over 20 minutes. RESULTS: Prolonged asymmetric smooth-pursuit stimulation induced a drift lasting >5 minutes in the direction of the prior pursuit. Upward drift was faster than downward drift and showed eye-position dependence in accordance with Alexander's law, but no increase of drift velocity with lateral gaze. Upward drift violated Listing's law in three of four subjects tested. CONCLUSIONS: An experimentally induced vertical smooth-pursuit imbalance leads to DBN in healthy human subjects. Accordingly, because in patients with cerebellar disease upward smooth-pursuit eye movements are typically better preserved than downward, the resultant sustained imbalance of vertical smooth-pursuit input may play a major role in the generation of DBN.
The authors describe three patients hospitalized for psychiatric disorders, all of whom had cerebellar lesions. Referring to recent research on nonmotor cerebellar functions, the authors suggest that patients with cerebellar lesions may develop an organic brain syndrome that closely resembles the organic brain syndrome associated with cerebral cortical lesions.
The cerebellum has traditionally been seen primarily to coordinate voluntary movement, but evidence is accumulating that it may play a role in cognition and behavior as well. This is a selective review of studies assessing potential cognitive deficits and personality changes associated with cerebellar disease. Preliminary studies of the role of the cerebellum in schizophrenia, dementia, and other psychiatric disorders are also discussed. Efforts to understand the neurological substrates of behavior should consider the role of the cerebellum.
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The present study is concerned with a clinical analysis of 17 patients with "rebound nystagmus" examined over a period of three years. All of them have shown a short duration second degree nystagmus evoked by changes in the direction of fixation, from the lateral to straight ahead gaze. This nystagmus was a fixation nystagmus, that is to say, it was enhanced in the presence of active optic fixation and inhibited in its absence. Almost all the patients (16 out of 17) had cerebellar signs on neurological examination (in one subject rebound nystagmus was the first sign suggesting cerebellar involvement and appeared several months before any other cerebellar sign was present). Rebound nystagmus was far more common than the other neuro-otological signs suggesting cerebellar dysfunction (vestibular hyperexcitability, dysrhythmia in postcaloric nystagmus and ocular dysmetria). In three out of four patients with unilateral lesions rebound nystagmus was ipsilateral with respect to the side of the lesion. Postmortem studies were carried out upon five cases and showed either pathological changes in the cerebellum or a lesion involving the cerebellar peduncles in the brain stem.
Facial nerve continuity was restored during cerebellopontine angle tumor removal in nine cases. The distal facial nerve was rerouted from the stylomastoid foramen into the cerebellopontine angle. Direct suture was accomplished in seven cases while two required interposition of a greater auricular nerve graft. There was excellent return of facial function in eight of the nine cases. Overall results are superior to nerve substitution techniques. The facial nerve should be inspected for continuity following tumor removal. If one is not certain the nerve is intact, the proximal facial stump should be identified at the brain stem and facial nerve continuity reestablished. A nerve substitution procedure should be resorted to a later time only when the proximal facial stump is not identifiable.
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Horizontal jerk nystagmus is indicative of a disorder involving the vestibular system. Periodic alternating nystagmus is a form of spontaneous nystagmus with a specific pattern. It is identified by the presence of spontaneous nystagmus in the primary direction of gaze, which beats in one direction for 1 or 2 minutes, followed by a null period, and then reappearance of the nystagmus in the opposite direction for a similar length of time. It may be congenital or acquired, and may be seen in association with vestibular-cerebellar disease or loss of vision. Recent case reports indicate that some forms of periodic alternating nystagmus may respond favorably to baclofen therapy.
Sarcoidosis is a chronic, idiopathic granulomatous disease with frequent pulmonary, ocular, and lymphatic systemic manifestations. Central nervous system involvement is rare (1% to 5%), yet the most frequent presenting symptoms (48%) in patients with neurosarcoidosis are neurologic. Eighth cranial nerve abnormalities occur in 20% of these patients, typically in association with other cranial neuropathies or overt systemic disease. Isolated eighth nerve disease is very rare. We report two cases of neurosarcoidosis manifest as isolated, sudden onset sensorineural hearing loss, one of which had a cerebellopontine angle (CPA) granuloma that mimicked an acoustic neuroma. Both patients experienced marked steroid-induced hearing improvement that persisted after termination of therapy. Brainstem evoked response audiometry (BSER) abnormality persisted despite normalization of audiologic parameters. The implications for diagnosis and treatment of sarcoidosis-induced hearing loss are described. Neurosarcoidosis must be considered when evaluating patients with sudden hearing loss. Prompt steroid therapy offers hope for significant hearing recovery in these patients.
Various hypotheses on the origin of cerebellar downbeat nystagmus (DBN) have been presented; the exact pathomechanism, however, is still not known. Based on previous anatomical and electrophysiological studies, we propose that an asymmetry in the distribution of on-directions of vertical gaze-velocity Purkinje cells leads to spontaneous upward ocular drift in cerebellar disease, and therefore, to DBN. Our hypothesis is supported by a computational model for vertical eye movements.
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An acute cerebellar hemorrhage in a 14-year-old girl was found to be caused by bleeding that had occured in an occult cerebellar astrocytoma. Such symptomatic hemorrhage into tumors, whether of metastatic or primary brain origin, occurs rarely but must be considered in patients of all ages who present with atypical strokes of presumed hemorrhagic etiology.
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We studied 55 cases of cerebellar atrophy identified by computerized tomography. Atrophy was determined by subjective assessment and objective measurements (superior cerebellar cistern, fourth ventricle, and brainstem). Different patterns of cerebellar atrophy were related to clinical diagnoses. A high incidence of vermal atrophy was observed in primary cerebellar degeneration and chronic alcoholism. More than half the patients with alcoholism had hemispheral atrophy. Vermal atrophy and enlargement of superior cerebellar cisterns (but not hemispheral atrophy) were associated with carcinomatous cerebellar degeneration. Atrophy caused by chronic phenytoin usage showed a specific pattern of enlargement of the cisterna magna, cerebellopontine angle, and superior cerebellar cisterns. Supratentorial atrophy was increased significantly only in the alcoholics. In general, limb ataxia, dysarthria, and nystagmus were related to hemispheral but not to vermal atrophy.