Levodopa reversible loss of the Piper frequency oscillation component in Parkinson's disease

Objectives-Although Parkinson's disease is typically characterised by brady kinesia, rigidity, and rest tremor, the possibility that two additional mot or deficits are manifest during small hand muscle activity was explored-nam ely, weakness and abnormal physiological tremor. Methods-A paradigm previously used in normal subjects reliably records the strength, tremor and surface EMG or index finger abducting contractions aga inst a compliant (elastic) resistance. In addition to the well known physio logical tremor at around 10 Hz, there are other co existing peak tremor fre quencies 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 park insonian patients while on and off dopaminergic medication. Results-The maximum strength of finger abduction produced by first dorsal i nterosseous contraction was considerably lower when patients were off medic ation (mean (SD) 6.27 (1.49) N when off v 12.33 (3.64) N when on). There wa s 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 wea ker contraction. Conclusion-As the components of physiological tremor at higher frequencies are thought to derive from CNS oscillations important in motor control, the ir loss in parkinsonism in association with severe off symptoms may represe nt an important pathophysiological link between dopaminergic depletion and parkinsonian motor deficits.