Ocular tilt reaction due to an upper brainstem lesion: paroxysmal skew deviation, torsion, and oscillation of the eyes with head tilt

Periodic alternating nystagmus and periodic alternating skew deviation in spinocerebellar ataxia type 6

The combination of periodic alternating nystagmus (PAN) and periodic alternating skew deviation (PASD) is rare. We report a case of PAN and PASD in a patient with spinocerebellar ataxia type 6 (SCA-6) and discuss the role of the cerebellum as a plausible mechanism for this combined pathologic condition.

Skew Deviation Revisited

Skew deviation is a vertical misalignment of the eyes caused by damage to prenuclear vestibular input to ocular motor nuclei. The resultant vertical ocular deviation is relatively comitant in nature, and is usually seen in the context of brainstem or cerebellar injury from stroke, multiple sclerosis, or trauma. Skew deviation is usually accompanied by binocular torsion, torticollis, and a tilt in the subjective visual vertical. This constellation of findings has been termed the ocular tilt reaction. In the past two decades, a clinical localizing value for skew deviation has been assigned, and a cogent vestibular mechanism for comitant and incomitant variants of skew deviation has been proposed. Our understanding of skew deviation as a manifestation of central otolithic dysfunction in different planes of three-dimensional space is evolving. The similar spectrum of vertical ocular deviations arising in patients with congenital strabismus may further expand the nosology of skew deviation to include vergence abnormalities caused by the effects of early binocular visual imbalance on the developing visual system.

Concurrent excitatory and inhibitory effects of high frequency stimulation: an oculomotor study

OBJECTIVE

To describe a reversible neurological condition resembling a crossed midbrain syndrome resulting from high frequency stimulation (HFS) in the midbrain.

METHODS

Postoperative evaluation of quadripolar electrodes implanted in the area of the subthalamic nucleus of 25 patients with Parkinson's disease (PD) successfully treated by HFS.

RESULTS

Four of the 25 patients experienced reversible acute diplopia, with dystonic posture and tremor in the contralateral upper limb when the white matter between the red nucleus and the substantia nigra was stimulated. The motor signs resembled those caused by lesions of the red nucleus. The ipsilateral resting eye position was "in and down" (three patients) or "in" (one patient). Enophthalmos was seen. Abduction was impaired and vertical eye movements were limited, but adduction was spared. The movements of the controlateral eye were normal. The ocular signs could be best explained by sustained hyperactivity of the extrinsic oculomotor nerve. Simultaneous tonic contraction of the superior rectus, the inferior rectus, and inferior oblique may cause the enophthalmos and partial limitation of upward and downward eye movements. Antagonist tonic contraction of the ipsilateral medial rectus severely impairs abduction.

CONCLUSION

This crossed midbrain syndrome, possibly resulting from simultaneous activation of oculomotor nerve and lesion-like inhibition of the red nucleus suggests that high frequency stimulation has opposite effects on grey and white matter.

Perceived vertical and lateropulsion: clinical syndromes, localization, and prognosis

We present a clinical classification of central vestibular syndromes according to the three major planes of action of the vestibulo-ocular reflex: yaw, roll, and pitch. The plane-specific syndromes are determined by ocular motor, postural, and perceptual signs. Yaw plane signs are horizontal nystagmus, past pointing, rotational and lateral body falls, deviation of perceived straight-ahead to the left or right. Roll plane signs are torsional nystagmus, skew deviation, ocular torsion, tilts of head, body, and perceived vertical in a clockwise or counterclockwise direction. Pitch plane signs are upbeat/downbeat nystagmus, forward/backward tilts and falls, deviations of the perceived horizon. The thus defined vestibular syndromes allow a precise topographic analysis of brainstem lesions according to their level and side. Special emphasis is placed on the vestibular roll plane syndromes of ocular tilt reaction, lateropulsion in Wallenberg's syndrome, thalamic and cortical astasia and their association with roll plane tilt of perceived vertical. Recovery is based on a functionally significant central compensation of a vestibular tone imbalance, the mechanism of which is largely unknown. Physical therapy may facilitate this central compensation, but this has not yet been proven in prospective studies.

Fast eye movement initiation of ocular torsion in mesodiencephalic lesions

Three patients with episodic ocular torsion and skew deviation due to mesodiencephalic lesions were studied by using binocular three-dimensional scleral search coils. The conjugate ocular torsion (upper pole of each eye rotating toward the side of the brainstem lesion) was initiated by a torsional fast eye movement. During prolonged episodes, torsional nystagmus was also present. Cessation of the ocular torsion and skew deviation occurred by slow eye movements with exponentially decreasing velocities in 2 patients, and by multiple fast torsional movements in 1 patient. In 1 patient, the abnormal eye movements were temporally linked to dystonic movements in the limbs on the side opposite the brainstem lesion. The occurrence of skew deviation with conjugate ocular torsion in brainstem lesions has been attributed to functional asymmetry in vestibular pathways responsible for the slow-phase compensatory eye movement response to roll. In comparison, the findings in our patients show that in mesodiencephalic lesions conjugate ocular torsion with skew deviation may be generated by torsional fast eye movements, indicating activation of the burst cells of the rostral interstitial nucleus of the medial longitudinal fasciculus.

Binocular vertical diplopia

The assessment of a patient with binocular vertical diplopia begins with a thorough history and neuro-ophthalmologic examination. The neuro-ophthalmologic examination includes observation for a compensatory head, face, or chin position; ocular ductions and versions in the nine cardinal positions of gaze; the three-step test; the double Maddox rod test; indirect ophthalmoscopy to observe the location of the fovea in relationship to the optic nerve head to determine cyclodeviation; and the forced ductions test. Binocular vertical diplopia may be due to supranuclear processes, ocular motor nerve dysfunction, neuromuscular junction disease, diseases of eye muscle, mechanical processes causing vertical eye misalignment, and even retinal disease. In this article, the differential diagnosis of these processes is outlined.

Vestibular syndromes in the roll plane: topographic diagnosis from brainstem to cortex

Central vestibular syndromes may be classified according to the three major planes of action of the vestibuloocular reflex, secondary to a lesional tone imbalance in either the horizontal yaw plane or the vertical pitch or roll plane. The clinical signs, both perceptual and motor, of a vestibular tone imbalance in the roll plane are ocular tilt reaction (OTR), ocular torsion, skew deviation and tilts of the perceived visual vertical (SVV). Either complete OTR or skew torsion without head tilt indicates a unilateral peripheral deficit of otolith input or a unilateral lesion of graviceptive brainstem pathways from the vestibular nuclei (crossing midline at the pontine level) to the interstitial nucleus of Cajal (INC) in the rostral midbrain. SVV tilts are the most sensitive sign of a vestibular tone imbalance in roll and occur with peripheral or central vestibular lesions from the labyrinth to the vestibular cortex. All tilt effects, perceptual, ocular motor and postural, are ipsiversive (ipsilateral eye undermost) with unilateral peripheral or pontomedullary lesions below the crossing of the graviceptive pathways. All tilt effects are contraversive (contralateral eye undermost) with unilateral pontomesencephalic brainstem lesions and indicate involvement of the medial longitudinal fasciculus or the rostral midbrain (INC). Unilateral lesions of vestibular structures rostral to the INC typically manifest with deviations of perceived vertical without concurrent eye-head tilt. OTR in unilateral paramedian thalamic infarctions indicates simultaneous ischemia of the paramedian rostral midbrain including the INC. Unilateral lesions of the posterolateral thalamus can cause thalamic astasia and moderate ipsiversive or contraversive SVV tilts, thereby indicating involvement of the vestibular thalamic subnuclei. Unilateral lesions of the parietoinsular vestibular cortex cause moderate, mostly contraversive SVV tilts. An SVV tilt found with monocular but not with binocular viewing is typical for a trochlear or oculomotor palsy rather than a supranuclear graviceptive brainstem lesion.

Vertical diplopia

An accurate clinical evaluation of vertical diplopia is predicated upon meticulous history-taking, observations regarding the presence and pattern of an anomalous head position, and the analysis of several subjective and objective tests of extraocular muscle function. To reach a final diagnosis with minimum risk and expense to the patient the examiner must be familiar with the neuroanatomy of the supranuclear and infranuclear pathways which control the actions of the vertically-acting extraocular muscles, the clinical methods and pitfalls of a number of clinical techniques which are used to identify an underacting extraocular muscle, and the hallmark characteristics of a supranuclear, infranuclear and restrictive ophthalmopathy.

Ocular torsion and tilt of subjective visual vertical are sensitive brainstem signs

Deviations of the position of the eye in the roll plane, ocular torsion (OT), and the subjective visual vertical (SVV) were systematically studied in 111 patients with acute vascular brainstem lesions. Of the 111 patients, 104 (94%) showed a direction-specific pathological tilt of the static SVV in our series. Seventy-one (83%) of 86 patients exhibited pathological static OT of one (47%) or both (36%) eyes. OT and SVV tilts are therefore sensitive signs in acute unilateral brainstem disorders. Measurements of SVV and OT may prove to be useful components of the neuro-ophthalmological evaluation. With respect to the directions of pathological tilt, SVV and OT are generally in the same direction. Based on neuroimaging, we conclude that all unilateral brainstem lesions caudal to the upper pons cause ipsiversive OT of one or both eyes, with concurrent ipsiversive tilts of SVV adjustments; all lesions rostral to this pontine level cause contraversive tilts of OT and SVV. Evidence is presented that pathological tilts of OT and SVV are secondary to a dysfunction of the tonic bilateral vestibular inputs that stabilize the eyes and head in normal upright position in the roll plane and dominate our perception of verticality.

Different types of skew deviation

Although all manifest skew deviations appear the same for the clinician, skew deviation can result from different combinations of dysconjugate vertical ocular deviations. Evidence is presented for three different types of skew deviation when it occurs as a feature of an ocular tilt reaction. In type 1 (utricle) there is upward deviation of both eyes with different amplitudes, as described for otolith Tullio phenomenon in humans. In Type 2 (dorsolateral medulla oblongata) hypertropia of one eye occurs while the other eye remains in the primary position, the hypothetical mechanism of skew deviation in Wallenberg's syndrome. In Type 3 (midbrain tegmentum) there is simultaneous hypertropia of one eye and hypotropia of the other eye, as described for electrical stimulation of midbrain tegmentum in monkeys and observed in clinical cases with a paroxysmal ocular tilt reaction.

Torsional nystagmus in the lateral medullary syndrome

Torsional nystagmus was recorded in 3 patients with the lateral medullary syndrome. Magnetic search coil oculography demonstrated slow phases of nystagmus of increasing, decreasing, and constant velocity. Neural integration of torsional eye velocity commands to position commands is impaired by lateral medullary infarction. Torsional pulsion of saccades, consisting of torsional fast eye movements induced during saccades downward or away from the side of infarction, was recorded in 2 patients. All patients had skew deviation with hypotropia on the side of brainstem damage. The torsional nystagmus beat away from the side of infarction in each patient, but in one it alternated direction as the eyes drifted about a neutral position of torsion. We attribute the torsional nystagmus to an imbalance of central projections from the anterior and posterior semicircular canals and the otolith receptors that mediate ocular counterroll.