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

• Published in: Brain (London, England : 1878) England : 1878), 2008-09, Vol.131 (9), p.2295-2303
• Main Authors: Bour, L. J., van Rootselaar, A. F., Koelman, J. H. T. M., Tijssen, M. A. J.
• Format: Article
• Language: English
• Subjects: Adult; Age Factors; Aged; Biological and medical sciences; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; downbeat nystagmus; Epilepsies, Myoclonic - complications; Epilepsies, Myoclonic - physiopathology; express saccades; Female; Fixation, Ocular; Humans; Male; Medical sciences; Middle Aged; myoclonic tremor; Neurology; Nystagmus, Pathologic - etiology; Nystagmus, Pathologic - physiopathology; Pursuit, Smooth; Saccades; SPEM; spinocerebellar ataxia; Spinocerebellar Ataxias - complications; Spinocerebellar Ataxias - physiopathology; Tremor - complications
• ISSN: 0006-8950; 1460-2156
• DOI: 10.1093/brain/awn177

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.