Pearls & Oy-sters: Oculopalatal tremor with one-and-a-half syndrome after pontine hemorrhage
Yasser Aladdin, MD,
James Scozzafava, MD, FRCPC,
Taim Muayqil, MD and
Maher Saqqur, MD
From the Division of Neurology, University of Alberta Hospital, Edmonton, AB, Canada.
Address correspondence and reprint requests to Dr. Maher Saqqur, Division of Neurology, University of Alberta Hospital, 2E3 Walter McKenzie Center, 8440-112 St., Edmonton, Alberta, Canada T6G 2B7
The palatal myoclonus in symptomatic cases is usually silentas the involved muscle is the levator veli palatini. This isin contrast to the audible clicking sound (generated by thesynchronous collapse of the eustachian tube) in patients withessential palatal myoclonus in which the involved muscle isthe tensor veli palatini.
The hyperintense signal on T2-weightedMRI in transneuronalhypertrophic degeneration of the inferiorolivary nucleus reflectsincreased water content and gliosis.Enlargement of the inferiorolivary nucleus results from astrocytichypertrophy and vacuolarcytoplasmic degeneration. Eventually,permanent atrophy of olivaryneurons ensues within 3 to 4 years.
A 63-year-old man with a history of treated hypertension presentedwith sudden onset of right hemiparesis and horizontal diplopiathat was worse on rightward gaze. His blood pressure was 220/120mm Hg. On neurologic examination, the patient had a right hemiplegia.Examination of the extraocular movements demonstrated conjugateleft lateral gaze palsy, impaired adduction of the left eye,and abduction nystagmus of the right eye. These signs were consistentwith a left "one and a half syndrome." Further assessment revealeda bilateral facial nerve palsy of the lower motor neuron type.The cranial CT revealed intraparenchymal brainstem hemorrhageinvolving the left side of the pontine tegmentum with extensioninto the fourth ventricle (figure 1). His motor weakness andthe facial diplegia improved, but the extraocular eye movementsremained limited with persistent horizontal diplopia, particularlyon rightward gaze.
Figure 1 Initial CT of the head showing the intraparenchymal brainstem hemorrhage that mainly involved the left side of the pontine tegmentum with extension into the fourth ventricle
Six months later, he presented again with a precipitous onsetof oscillopsia with exaggerated sense of motion and blurringof the visual world during head movements, particularly whilewalking or driving. On examination, a new finding of a verticalpendular nystagmus was observed with larger amplitude in theright eye (video 1). Another finding of a palatal tremor wasnoted which was more prominent on the right side (video 2).On further inquiry, he did not describe any specific bulbarcomplaint that could be linked to his palatal tremor. He alsowas not aware of any unusual noise or clicking sounds in hisears. The palatal tremor persisted during sleep while the pendularnystagmus disappeared. Cranial MRI showed an enlargement ofthe left inferior olivary nucleus with a hyperintense signalon T2-weighted images (T2WI) (figure 2). The clinical presentationsupported by the imaging was consistent with the diagnosis ofoculopalatal tremor. The patient was initially treated by atrial of gabapentin for symptomatic relief, but this aggravatedthe dizziness. He was subsequently prescribed clonazepam withsignificant improvement in his symptoms despite the persistenceof the ocular and palatal tremors.
Figure 2 Axial FLAIR MRI at the level of the inferior olives revealing the high signal intensity and the hypertrophy of the left inferior olivary nucleus
Palatal tremor (PT) is a segmental myoclonus involving the musclesof the soft palate. The movement consists of rhythmic and repetitive,rather than oscillatory, contractions of the agonist musclesonly. Occasionally, this hyperkinetic movement may spread toinvolve adjacent structures derived from the brachial arch suchas the larynx and the pharyngeal wall.1 Oculopalatal tremor(OPT) refers to the synchronous or asynchronous combinationof PT and pendular nystagmus. The pendular nystagmus can besymmetric or asymmetric in amplitude with vertical, torsional,or mixed trajectories. Symptomatic PT is usually the delayedsequela of lesions interrupting the Guillain-Mollaret triangle(GMT) and typically manifests several months after the acuteevent. The myoclonus is generated by the levator veli palatinimuscle innervated by the nucleus ambiguous through the facialor glossopharyngeal nerves.
Symptomatic PT is often the result of an ischemic or hemorrhagicstroke disrupting the GMT, but also can result from other lesionsto this area such as demyelination and space-occupying lesions.The GMT is the dentato-rubro-olivary pathway that connects thedentate nucleus with the contralateral red nucleus through thesuperior cerebellar peduncle (SCP), the red nucleus with theipsilateral inferior olivary nucleus (ION) through the centraltegmental tract (CTT), and the ION back to the contralateraldentate nucleus via the inferior cerebellar peduncle (ICP).The topographic localization of the lesions can therefore belocalized to 1) dentate nucleus, 2) SCP, 3) decussation of SCP,4) red nucleus, 5) CTT, or 6) ICP.2 In our patient, the lesiondisrupted the left CTT.
The etiopathology of symptomatic OPT is related to transneuronalhypertrophic degeneration of the ION in response to deafferentation.The gamma-aminobutyric acid (GABA)-dependent synaptic transmissionwithin GMT modulates the rhythmic excitation and inhibitionof inferior olivary neurons. OPT is thought to arise from hypersynchronousfiring of olivary neurons due to interruption of the supranuclearGABAergic control.3,4 This abnormal rhythm is subsequently transmittedthrough ICP to the contralateral cerebellar flocculus and, thus,interferes with physiologic regulations of the oculomotor system.Disruption of the left CTT in this case resulted in hypersynchronousfiring from the left ION toward the right cerebellar flocculus.Impaired supranuclear control over the left ION, therefore,may explain the higher amplitude of nystagmus in the contralateraleye. Alternatively, the pendular nystagmus in OPT has been postulatedto result from an impaired adaptation of the vestibulo-ocularreflex (VOR) due to degeneration of the ION. Recently, the pendularnystagmus has been linked to the structural distortion of theadjacent vertical neural integrators or their efferent projectionseither by the primary lesion or by the hypertrophied ION.4
The horizontal one-and-a-half syndrome is characterized by ipsilateralconjugate horizontal gaze palsy and internuclear ophthalmoplegia.The combination results from a unilateral pontine lesion involvingthe paramedian pontine reticular formation or the abducens nucleusand the ipsilateral medial longitudinal fasciculus. The associationbetween one-and-a-half syndrome and subsequent development ofOPT has been initially described by Wolin et al.5 In that series,all of the five patients had concomitant facial nerve palsyduring their initial presentations. The facial nucleus liesin the close vicinity of the CTT within the pontine tegmentumand the facial nerve fascicles can predictably be injured asthey sweep around the abducens nucleus. This close anatomicproximity suggests that the concomitant facial palsy may bea predictor of subsequent OPT after the one-and-a-half syndrome.Nevertheless, the predictive value of an initial facial palsymay not be established from that retrospective review or fromthis case report.5
Pathologically, the olivary enlargement results from neuronaland astrocytic hypertrophy with vacuolar cytoplasmic degeneration.Disintegration of the ION occurs in a few years with dissolutionand eventually permanent atrophy of olivary neurons.6 Temporalcorrelation of the pathologic processes is demonstrated on imagingstudies with high signal intensity of ION on T2WI reflectingthe increased water content and gliosis within the ION. Thehigh-intensity signal within the ION appears as early as 3 weeksafter the initial lesion and may persist for 3 to 4 years beforepermanent olivary atrophy ensues.7
In approximately one quarter of cases, however, no structurallesion can be found and the condition is termed "essential palataltremor." Unlike symptomatic PT, essential PT involves the tensorveli palatini muscle which is innervated by the trigeminal nerve.The involvement of the tensor veli palatine muscle accountsfor the audible clicking sounds often perceived by patientswith essential PT and is due to the collapse of the eustachiantubes, the site of insertion of the tensor veli palatini muscle.In contrast to symptomatic PT, essential PT is not associatedwith abnormal ocular oscillations and the myoclonus tends todissipate during sleep.1
The treatment of PT has involved traditional agents used formyoclonus and tremor, particularly GABA agonists such as gabapentinand benzodiazepines. Other pharmacotherapies have been usedwith variable success including baclofen, anticholinergics,and antiepileptic drugs. Successful control of essential PThas also been achieved with botulinum toxin injections intothe tensor veli palatini muscle. Our patient had a good responseto clonazepam with significant improvement in his symptoms.The symptomatic improvement may be theoretically related tothe enhanced GABAergic transmission within the GMT. Arguably,the improvement in the oscillopsia might be attributed to differentcompensation mechanisms which characterize the natural courseof this phenomenon.
Deuschl G, Wilms H. Clinical spectrum and physiology of palatal tremor. Mov Disord 2002;17:S63–S66.
Jellinger K. Hypertrophy of the inferior olives: report on 29 cases. Z Neurol 1973;205:153–174.[Medline]
Sotelo C, Gotow T, Wassef M. Localization of glutamic-acid decarboxylase-immunoreactive axon terminals in the inferior olives of the rat, with special emphasis on anatomical relations between GABAergic synapses and dendrodendritic gap junctions. J Comp Neurol 1986;252:32–50.[Medline]
Kim JS, Moon SY, Choi KD, Kim JH, Sharpe JA. Patterns of ocular oscillation in Oculopalatal tremor: imaging correlations. Neurology 2007;68:1128–1135.[Abstract/Free Full Text]
Wolin MJ, Trent RG, Lavin PJ, Cornblath WT. Oculopalatal myoclonus after the one-and-a-half syndrome with facial nerve palsy. Ophthalmology 1996;103:177–180.[Medline]
Goto N, Kaneko M. Olivary enlargement: chronological and morphometric analyses. Acta Neuropathol 1981;54:275–282.[Medline]
Goyal M, Versnick E, Tuite P, et al. Hypertrophic olivary degeneration: Metaanalysis of the temporal evolution of MR findings. AJNR Am J Neuroradiol 2000;21:1073–1077.[Abstract/Free Full Text]
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