Journal of Neurological Sciences 151 (1997) 169–176 Analysis of single-joint rapid movements in patients with sporadic olivopontocerebellar atrophy a b, c d e * M. Manto , E. Godaux , J. Hildebrand , J. van Naemen , J. Jacquy a Belgian National Fund for Scientific Research, Free University of Brussels, 1070 Brussels, Belgium b Department of Neurophysiology, Faculty of Medicine, University of Mons, 7000 Mons, Belgium c ˆ Department of Neurology, Hopital Erasme, 1070 Brussels, Belgium d ˆ Cyclotron Biomedical, Hopital Erasme, 1070 Brussels, Belgium e ˆ Department of Neurology, Hopital Civil de Charleroi, 6000 Charleroi, Belgium Received 9 September 1996; revised 6 March 1997; accepted 21 March 1997 Abstract Patients with pure cerebellar cortical atrophy (CCA) present isolated cerebellar signs, whereas patients with sporadic olivopontocerebel- lar atrophy (sOPCA) present various combinations of cerebellar and extracerebellar signs. However, the differential diagnosis between these two forms of cerebellar degeneration is often a challenge for the clinician. Therefore, any test helping in this differential diagnosis might have a potential clinical interest. In this study, our goal was to investigate the adaptation to increased inertia in patients with sOPCA exhibiting combined cerebellar and pyramidal signs, during the performance of fast wrist flexions. We found that these patients exhibited a hypermetria which remained unchanged after addition of inertia, because they were unable to increase neither their agonist activity (launching force), nor their antagonist activity (braking force). This contrasts with our previous findings in patients with CCA. In these latter, the hypermetria worsened when the inertial load of the hand increased because those patients were able to increase their agonist activity, but not their antagonist activity. The adaptation to inertia might thus help to differentiate CCA and sOPCA.  1997 Elsevier Science B.V. Keywords: Olivopontocerebellar atrophy; Cerebellum; Hypermetria; Inertial loads; EMG triphasic pattern; Cortical cerebellar atrophy 1. Introduction activity in the antagonist muscle (the braking force), followed by another burst in the agonist. The most Hypermetria is a classical cerebellar symptom designat- prominent EMG abnormality associated with cerebellar ing the overshoot observed when a patient is asked to hypermetria has been repeatedly reported to be a delayed make a very fast and accurate movement (Holmes, 1917, onset of the antagonist activity (Conrad and Brooks, 1974; 1922, 1939; Gilman et al., 1981). Such type of movement Hallett et al., 1975; Flament and Hore, 1986; Hallett et al., is controlled by a triphasic pattern of electromyographic 1991; Gilman, 1994). (EMG) activity (Hallett et al., 1975; Hallett and Marsden, Moreover, in a previous study (Manto et al., 1994), we 1979; Meinck et al., 1984; Hannaford and Stark, 1985; have analysed the effects of an artificial increase of the Wierzbicka et al., 1986; Karst and Hasan, 1987; Stein et inertial load on ballistic wrist flexion movements in a al., 1988; Wierzbicka and Wiegner, 1992; Wiegner and group of patients with isolated cerebellar signs, including Wierzbicka, 1992). A burst of activity in the agonist patients with a cerebellar atrophy after a course of more muscle (the launching force) is followed by a burst of than 10 years. These patients exhibited a hypermetria which worsened when the inertia of the moving hand was * artificially increased. While a normal subject adapts him- Corresponding author. University of Mons, Place du Parc 20, 7000 Mons, Belgium. Tel: +32 65 373570; fax: +32 65 373054. self to increasing inertia by increasing both the agonist and 0022-510X / 97 / $17.00  1997 Elsevier Science B.V. All rights reserved PII S0022-510X(97)00123-8