Regularity of force tremor in Parkinson's disease

• Published in: Clinical neurophysiology Vol. 112; no. 9; pp. 1594 - 1603
• Main Authors: Vaillancourt, David E., Slifkin, Andrew B., Newell, Karl M.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.09.2001; Elsevier Science
• Subjects: Adult; Aged; Aged, 80 and over; Biological and medical sciences; Biomarkers; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Female; Force tremor; Hand Strength; Humans; Male; Medical sciences; Neurology; Oscillometry; Parkinson Disease - physiopathology; Parkinson’s disease; Regularity; Severity of Illness Index; Time Factors; Time series; Tremor - physiopathology; Unified Parkinson’s disease rating scale; Force tremor; Unified Parkinson’s disease rating scale; Regularity; Parkinson’s disease; Time series; Human; Gripping; Nervous system diseases; Load; Tremor; Force; Parkinson disease; Muscle contraction; Motor control; Cerebral disorder; Involuntary movement; Central nervous system disease; Oscillation; Degenerative disease; Neurological disorder; Elderly; Extrapyramidal syndrome
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/S1388-2457(01)00593-4

Objectives: The study examines the time-dependent structure of force tremor to investigate two hypotheses: (1), the regularity of tremor can help in discriminating normal aging from that of Parkinson's disease (PD); and (2), there is increased tremor regularity with increases in the severity of PD. Methods: Eight young (21–29 years), eight elderly (68–80 years), and eight PD (68–80 years) subjects produced constant grip force at 5, 25 and 50% of their maximal voluntary contraction by squeezing two load cells with their index finger and thumb under a vision and no vision condition. Spectral analysis and approximate entropy (ApEn) were used, respectively, to analyze the frequency and time-dependent structure of tremor. Results: The analyses showed that there were no differences in the amplitude and modal frequency of force tremor between groups. The ApEn was significantly lower in the PD group compared with the controls. For the PD group, the linear relations between the total scores taken from the Unified Parkinson's Disease Rating Scale-motor section and the dependent variables were r 2=0.71 ( P<0.01) for ApEn, r 2=0.20 ( P>0.05) for the modal frequency, and r 2=0.23 ( P>0.05) for the standard deviation. Surrogate analyses revealed that the time-dependent structure of tremor provided additional information beyond that of amplitude and modal frequency analyses. Conclusions: These findings indicate that tremor analyses should not be limited to just the frequency and amplitude of the oscillation, and that the time-dependent structure of tremor is useful in differentiating tremor in healthy people from those with PD. The hypothesis that more regular tremor in PD is due to a loss of multiple neuronal oscillators contributing to the tremor output is discussed.