Central vestibular syndromes in roll, pitch, and yaw planes: Topographic diagnosis of brainstem disorders
(Impact Factor: 0.18).
07/2009; 15(6):291-303. DOI: 10.3109/01658109509044618
Evidence is presented for a clinical classification of central vestibular syndromes according to the three major planes of action of the vestibulo-ocular reflex (VOR): yaw, pitch, and roll. The plane-specific vestibular syndromes are determined by ocular motor, postural, and perceptual signs. Roll plane signs are: torsional nystagmus, skew deviation, ocular torsion, tilts of head, body, and perceived vertical; pitch plane signs are: upbeat/downbeat nystagmus, forward/backward tilts and falls, deviations of perceived horizontal; yaw plane signs are: horizontal nystagmus, past pointing, rotational and lateral body falls, deviation of perceived straight-ahead. The thus defined VOR syndromes allow for a precise topographic diagnosis of brainstem lesions as to their level and side. A tone imbalance in roll indicates unilateral lesions (ipsiversive at pontomedullary level, contraversive at pontomesencephalic level). A tone imbalance in pitch indicates bilateral (paramedian) lesions or bilateral dysfunction of the flocculus. It is hypothesized that signal processing of the VOR in roll and pitch is conveyed by the same rather than separate ascending pathways in the medial longitudinal fasciculus and the brachium conjunctivum. A unilateral lesion (or stimulation) of these ‘graviceptive’ pathways (which transduce input from vertical semicircular canals and otoliths) affects function in roll, whereas bilateral lesions (or stimulation) affects function in pitch. Thus, the vestibular system is able to change its functional plane of action from roll to pitch by switching from a unilateral to a bilateral mode of operation. Therefore a common integrator system is efficient (and sufficient) for both eye movements in roll and pitch (rostral interstitial nucleus of the medial longitudinal fasciculus and rostral interstitial nucleus of Cajal). Clinically this means that bilateral syndromes in roll (skew torsion) manifest in a syndrome in pitch (upbeat- or downbeat nystagmus). Pure syndromes in yaw are rare, since the small causative area covering the medial and superior vestibular nucleus is not only adjacent to but overlapped by the structures also subserving roll and pitch function. A lesion frequently results in mixed (e.g., torsional and horizontal) nystagmus. The lesional sites of yaw syndromes are restricted to the pontomedullary level because of the short distance between the vestibular nuclei and the integration center for horizontal eye movements in the paramedian pontine reticular formation. Syndromes in roll and pitch, however, may arise from brainstem lesions located in an area extending from the medulla to the mesencephalon, an area corresponding to the large distance between the vestibular nuclei and the integration centers for vertical and torsional eye movements in the rostral midbrain.
Available from: Stefan Glasauer
- "The upward drift of DBN consists of a gaze-evoked drift, which is hypothesized to be due to an impaired neural integrator function, and a spontaneous upward drift during gaze straight ahead (Straumann et al., 2000; Glasauer et al., 2003). Three different pathomechanisms are thought to cause the spontaneous upward drift: (i) a tone imbalance of the central vestibular pathways of the vertical eye movements (Baloh and Spooner, 1981; Halmagyi et al., 1983; Brandt and Dieterich, 1995; Böhmer and Straumann, 1998), including otolith pathways as suggested by the finding that DBN is gravity dependent (Marti et al., 2002; Sprenger et al., 2006), (ii) an imbalance of the vertical smooth pursuit tone in which the imbalance of upward visual velocity commands results in spontaneous upward drift (Zee et al., 1974) and (iii) a mismatch in the 3D neural coordinate system for vertical saccade generation due to a defect of the neural velocity-to-position integrator for gaze holding (Glasauer et al., 2003). Marti et al. (2005) proposed a mechanism by which floccular deficiency causes DBN. "
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ABSTRACT: Downbeat nystagmus (DBN), the most common form of acquired fixation nystagmus, is often caused by cerebellar degeneration, especially if the vestibulo-cerebellum is involved. The upward ocular drift in DBN has a spontaneous and a vertical gaze-evoked component. Since cerebellar involvement is suspected to be the underlying pathomechanism of DBN, we tested in 15 patients with DBN whether the application of the potassium-channel blocker 4-aminopyridine (4-AP), which increases the excitability of cerebellar Purkinje cells as shown in animal experiments, reduces the vertical ocular drift leading to nystagmus. Fifteen age-matched healthy subjects served as the control group. 4-AP may affect spontaneous drift or gaze-evoked drift by either enhancing visual fixation ability or restoring vision-independent gaze holding. We therefore recorded 3D slow-phase eye movements using search coils during attempted fixation in nine different eye positions and with or without a continuously visible target before and 45 min after ingestion of 10mg 4-AP. Since the effect of 4-AP may depend on the associated etiology, we divided our patients into three groups (cerebellar atrophy, n = 4; idiopathic DBN, n = 5; other etiology, n = 6). 4-AP decreased DBN during gaze straight ahead in 12 of 15 patients. Statistical analysis showed that improvement occurred predominantly in patients with cerebellar atrophy, in whom the drift was reduced from -4.99 +/- 1.07 deg/s (mean +/- SE) before treatment to -0.60 +/- 0.82 deg/s afterwards. Regression analysis of slow-phase velocity (SPV) in different eye positions revealed that vertical and horizontal gaze-evoked drift was significantly reduced independently of the patient group and caused perfect gaze holding on the average. Since the observed improvements were independent of target visibility, 4-AP improved fixation by restoring gaze-holding ability. All in all, the present study demonstrates that 4-AP has a differential effect on DBN: drift with gaze straight ahead was predominantly reduced in patients with cerebellar atrophy, but less so in the remaining patients; 4-AP on the average improved neural integrator function, i.e. gaze-evoked drift, regardless of etiology. Our results thus show that 4-AP was a successful treatment option in the majority of DBN patients, possibly by increasing Purkinje cell excitability in the cerebellar flocculi. It may work best when DBN is associated with cerebellar atrophy. Furthermore, 4-AP may be a promising treatment option for patients with a dominant gaze-evoked component of nystagmus, regardless of its etiology.
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ABSTRACT: A group of cells lying along the midline of the mid-medulla, nucleus pararaphales, is shown to play a role in vertical eye movements. Its efferents project along the midline, then pass laterally to follow the ventral external arcuate fibers around the surface of the medulla into the restiform body. The fibers terminate in the flocculus and ventral paraflocculus. This nucleus is one of the "cell groups of the paramedian tracts," which, based on their connectivity, could provide a motor-feedback signal for eye-head position to the cerebellum. Lesions of these pathways could lead to gaze-evoked nystagmus.
Available from: mayoclinicproceedings.com
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ABSTRACT: 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.
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