Levodopa reversible loss of the Piper frequency oscillation component in Parkinson's disease
- aMRC Human Movement and Balance Unit, Institute of Neurology, 23 Queen Square, London WC1N 3BG, UK, bUniversity Department of Clinical Neurology, cSchool of Kinesiology and Department of Psychology, University of Illinois, Chicago, USA, and Department of Neurological Sciences, Rush Medical College, Chicago, USA
- Dr J H McAuley
- Received 16 December 1999
- Revised 29 November 2000
- Accepted 19 December 2000
OBJECTIVES Although Parkinson's disease is typically characterised by bradykinesia, rigidity, and rest tremor, the possibility that two additional motor deficits are manifest during small hand muscle activity was explored—namely, weakness and abnormal physiological tremor.
METHODS A paradigm previously used in normal subjects reliably records the strength, tremor and surface EMG of index finger abducting contractions against a compliant (elastic) resistance. In addition to the well known physiological tremor at around 10 Hz, there are other co existing peak tremor frequencies at around 20 and 40 Hz; the last of these frequencies corresponds to the range of EMG Piper rhythm. The same technique was used to study parkinsonian patients while on and off dopaminergic medication.
RESULTS The maximum strength of finger abduction produced by first dorsal interosseous contraction was considerably lower when patients were off medication (mean (SD) 6.27 (1.49) N when off v 12.33 (3.64) N when on). There was also a marked reduction in the power of Piper frequency finger tremor (p<0.0005) and EMG (p<0.0005) oscillations that did not simply result from weaker contraction.
CONCLUSION As the components of physiological tremor at higher frequencies are thought to derive from CNS oscillations important in motor control, their loss in parkinsonism in association with severe off symptoms may represent an important pathophysiological link between dopaminergic depletion and parkinsonian motor deficits.
↵† died 28 September 1998