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Brain Advance Access published online on August 7, 2008
Brain, doi:10.1093/brain/awn177
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© The Author (2008). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Oculomotor abnormalities in myoclonic tremor: a comparison with spinocerebellar ataxia type 6

L. J. Bour1,2, A. F. van Rootselaar1,2, J. H. T. M. Koelman1,2 and M. A. J. Tijssen1

1Department of Neurology and 2Department of Clinical Neurophysiology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands

Correspondence to: L. J. Bour, PhD, Department of Clinical Neurophysiology, Academic Medical Center, D2 KNF, P.O. Box 22660, 1100 DD Amsterdam, The Netherlands E-mail: bour{at}amc.nl

In the present study, eye movements are recorded in two patient groups with an autosomal dominantly inherited cerebellar disorder, i.e. spinocerebellar ataxia type 6 (SCA6) and familial cortical myoclonic tremor with epilepsy (FCMTE). In SCA6 and FCMTE patients striking similarities with the extensive Purkinje cell changes in the cerebellar cortex were described, but the two disorders have a distinctive clinical picture. SCA6 is a late-onset cerebellar syndrome, with relatively minimal brain stem and cerebral cortex symptoms. In contrast, FCMTE is clinically characterized by cortical symptomatology with a distal cortical myoclonic tremor and infrequent epileptic attacks without cerebellar dysarthria and limb ataxia. Comparison of oculomotor function of six FCMTE patients, five SCA6 patients and 18 healthy controls demonstrated both in SCA6 patients and FCMTE patients square wave jerks, downbeat nystagmus (DBN) and a stronger reduced downward smooth pursuit gain than an upward smooth pursuit gain. Only in SCA6 patients horizontal smooth pursuit gain was reduced. Except for the downward direction mean saccadic gain in both patient groups was reduced. This is consistent with cerebellar cortical pathology in both disorders. Subsequently, both patient groups showed increase of DBN with hyperventilation. As a novel finding, only the FCMTE patients showed a significantly increased amount of express saccades in the pro-saccade paradigm.

Key Words: myoclonic tremor; spinocerebellar ataxia; SPEM; downbeat nystagmus; express saccades

Abbreviations: SPEM, smooth-pursuit eye movement; FCMTE, familial cortical myoclonic tremor with epilepsy; SCA6, spinocerebellar ataxia type 6; SCA, spinocerebellar ataxias; SEP, sensory evoked potential; TMS, transcranial magnetic stimulation; AED, anti-epileptic drug; DMI, double magnetic induction; HV, hyperventilation; DBN, downbeat nystagmus; DLPFC, dorsolateral prefrontal cortex; SCi, superior colliculus inferior; SNr, substantia nigra pars reticulate; Vmax(20), the estimated peak saccade velocity at 20 degrees

Received March 26, 2008. Revised June 3, 2008. Accepted July 6, 2008.


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