Essential tremor and cerebellar dysfunction: abnormal ballistic movements
- 1Neurologische Universitätsklinik Freiburg, Freiburg, Germany
- 2Neurologische Universitätsklinik Kiel, Niemannsweg, Kiel, Germany
- 3Zentrum für Datenanalyse und Modellbildung, Fakultät für Physik, University of Freiburg, Freiburg, Germany
- Correspondence to: Prof Dr C H Lücking, Neurologische Universitätsklinik Freiburg, Breisacher Str 64, 79106 Freiburg, Germany; luecking{at}nz11.ukl.uni-freiburg.de
- Received 4 January 2001
- Accepted 3 July 2002
- Revised 20 June 2002
Abstract
Background: Clinical characteristics reminiscent of cerebellar tremor occur in patients with advanced essential tremor. Ballistic movements are known to be abnormal in cerebellar disease. The hypothesis was proposed that ballistic movements are abnormal in essential tremor, reflecting cerebellar dysfunction.
Objective: To elucidate the role of the cerebellum in the pathophysiology of essential tremor.
Methods: Kinematic parameters and the triphasic electromyographic (EMG) components of ballistic flexion elbow movements were analysed in patients assigned to the following groups: healthy controls (n = 14), pure essential postural tremor (ETPT; n = 17), and essential tremor with an additional intention tremor component (ETIT; n = 15).
Results: The main findings were a delayed second agonist burst (AG2) and a relatively shortened deceleration phase compared with acceleration in both the essential tremor groups. These abnormalities were most pronounced in the ETIT group, which had additional prolongation of the first agonist burst (AG1) and a delayed antagonist burst (ANT).
Conclusions: Abnormalities of the triphasic pattern and kinematic parameters are consistent with a disturbed cerebellar timing function in essential tremor. These abnormalities were most pronounced in the ETIT group. The cerebellar dysfunction in essential tremor could indicate a basic pathophysiological mechanism underlying this disorder. ETPT and ETIT may represent two expressions within a continuous spectrum of cerebellar dysfunction in relation to the timing of muscle activation during voluntary movements.
- AG1, first agonist burst within the triphasic electromyographic (EMG) pattern
- AG2, second agonist burst within the triphasic EMG pattern
- Amax, maximum acceleration of movement
- ANT, first antagonistic burst within the triphasic EMG pattern
- ETIT, essential tremor with an additional intention tremor component
- ETPT, essential tremor with an isolated postural tremor
- T1, time required to accelerate the movement from zero to maximum velocity
- T2, time required to decelerate the movement from maximum velocity to zero
- TP, tremor period (duration of one tremor cycle)
- TPball, period of tremor induced by a ballistic movement
- TPpost, period of postural tremor derived from spectral analysis
- Vmax
- maximum velocity of movement
