Case #1
A 41 yo male alcoholic with progressive ataxia, oscillopsia and poor
coordination.
Case History: A 41 yo male alcoholic presented with
progressive ataxia, oscillopsia and poor coordination. On exam he
was alert, oriented and cooperative, with a violent intention tremor
worse on the right. He had decreased up gaze, slow upward saccades
and a mild esophoria that was worse on lateral gaze to both sides.
He had an upbeating nystagmus that became worse when he looked left
and reversed to downbeating on right gaze. Convergence did not
change the nystagmus and there was no skew deviation. The horizontal
VOR to slow and rapid head movements was normal. There was no post
headshaking nystagmus.
Discussion: Localization in this case is not
straightforward. The violence of the patient's tremor suggests a
rubral or cerebellar outflow tremor. A limitation in upgaze and the
slow vertical saccades suggests an abnormality in the midbrain (rostral
interstitial nucleus of the medial longitudinal fasciculus (riMLF)).
An esophoria that is worse or only present on lateral gaze is
indicative of a bilateral sixth nerve palsy.
Upbeating nystagmus may be due to a bilateral interruption of the
inputs from the anterior semicircular canals (SCC), which are
responsible for upward slow phase eye movements. This would cause a
spontaneous downward slow phase due to the resting tone provided by
the posterior canals, followed by a resetting quick phase.
The anterior canal inputs synapse in the ipsilateral superior,
lateral and medial vestibular nuclei. The secondary neurons cross
the midline in the brachium conjunctivum (BC), ventral tegmentum
(VT), and to a lesser extent in the MLF. The posterior canals
transmit their signals exclusively via the MLF. Imbalance in resting
tone can then develop due to lesions in any of the three tracts. An
MLF lesion would result in a downbeating nystagmus and possibly a
skew deviation as well as an internuclear opthalmoplegia. A BC or VT
lesion might lead to an upbeating nystagmus.
Another cause of upbeat nystagmus could be an abnormality of the
vertical neural integrator which is located in the interstitial
nucleus of Cajal. If the origin of the tremor is rubral it would
support this localization since the red nucleus and the interstitial
nucleus of Cajal are near each other.
Vertical gaze holding difficulty is also described with injury to
the vestibulo-cerebellum. Other central localizations of upbeat
nystagmus are the medulla (bilateral lesions of the nucleus
prepositus hypoglossi), the anterior visual pathways (in children),
and the thalamus. Etiologies of upbeat nystagmus also include a
transient finding in infants, brain stem masses, Multiple Sclerosis,
Wernicke's encephalopathy, brain stem encephalitis, Bechet's
syndrome, meningitis, and organophosphate poisoning.
Etiology: Wernicke's Encephalopathy. This patient
had been previously diagnosed with thiamine deficiency. It is likely
that he returned to his poor diet allowing for return and
progression of his disease. One unusual aspect of this patient's
ocular motor findings was the combination of an up and a downbeating
nystagmus; which appeared depended upon the direction of gaze.
Patients with Wernicke's encephalopathy often have upbeating
nystagmus that changes to downbeating with convergence, and
sometimes vice versa, but to have a vertical nystagmus that changes
direction as a function of horizontal eye position is unusual. This
finding may related to an abnormality in the vestibular mechanism
that ensures that the eyes rotate around an axis that is parallel to
the axis of head rotation, no matter what the position of the eye in
the orbit.
Original Date: Feb 10, 1995
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