Action tremor during object manipulation in Parkinson's disease

Abstract

In previous studies of fingertip forces during precision grip in subjects with Parkinson's disease (PD), we observed regular oscillations in isometric force. The present study characterizes the nature of these oscillations. Fingertip forces were recorded from the index finger and thumb during precision grip‐lifts with a 300 g and 900 g object in 10 subjects with PD and 20 healthy control subjects. Fourier analysis confirmed that all subjects with PD exhibited force oscillations with a clearly definable frequency (∼7–11 Hz). Five of these subjects also exhibited a second lower frequency peak (∼5 Hz). Approximately half of the 20 control subjects displayed a single frequency peak (∼8–12 Hz), which was generally lower in amplitude than in the subjects with PD (representing enhanced physiological tremor), whereas the remaining control subjects had low‐amplitude, broad‐based spectra (representing physiological tremor). The amplitude of the force oscillations was higher for lifts with the heavier object in both the control subjects and subjects with PD. l‐Dopa resulted in a decreased tremor amplitude but did not influence the frequency. The force oscillations of the two opposing digits normal to the grip surfaces were in phase, whereas the oscillations tangential to the grip surfaces were often out of phase. The results suggest that the multipeaked force rate trajectories reported previously are caused by action tremor. The similarity of force oscillations in subjects with PD and healthy control subjects suggests common tremor‐generating mechanisms and supports the notion that the parkinsonian action tremor (AT) is an exaggerated form of physiological tremor. These findings provide insight into the impaired hand function observed in individuals with PD.

Electrophysiologic characteristics of tremor in Parkinson?s disease and essential tremor

“…Kraus et al 12 studied a large sample of 870 PD patients showing that a combination of rest, postural and kinetic tremors constitute the most frequent tremor phenotype in PD. While some consider this tremor to be an occasional and unimportant finding, in clinical practice, a moderate action tremor may be more dysfunctional than typical parkinsonian rest tremor 13 . As in the case of rest tremor in ET, the basis for action tremor in PD is unclear.…”

Subgroup analysis of PD tremor with loading: Action tremor as a combination of classical rest and physiological tremor

“…PD tremor is classically described as a low-frequency (3.5-6.5 Hz) asymmetric pill-rolling resting tremor of the limbs different than essential tremor or physiological tremor. It is generally accepted that PD tremor is centrally originated but may be more complex, involving more than one neurological circuit (Findley et al, 1981;Forssberg et al, 2000;Wenzelburger et al, 2000). Currently, pharmacological management of PD primarily involves the use of dopaminergic replacement therapy.…”

“…Enhanced physiological tremor presents in situations of stress, forceful muscle contraction, fatigue, or with adrenergic medication, as a large amplitude peaked spectrum between 8 and 12 Hz of predominant stretch-reflex origin (Allum, 1984). General physiological hand tremor can occur in the approximate range of 3-17 Hz (Beuter et al, 2003;Forssberg et al, 2000;Raethjen et al, 2000). While patients with PD may exhibit physiological tremor in addition to PD tremor, it is unknown whether this presentation of physiological tremor show similarity to that of controls.…”

“…Loading and spectral examination of the resulting tremor within and above the PD frequency band can provide detailed information on peripheral (load-dependent) or central (load-independent) tremor components (Burne et al, 2004). Isolated observations of PD and physiological bands have demonstrated significant change in frequency and amplitude of tremor with loading (Forssberg et al, 2000;Raethjen et al, 2005). At present, torques of 0.2-1.2 N.m (Burne et al, 2004), loads of 100-900 g (Forssberg et al, 2000;Meshack and Norman, 2002;Raethjen et al, 2005), or 0-25% of individualized maximum voluntary contraction (MVC) has been used to investigate focal hand tremor but has not been standardized (Heroux et al, 2009).…”

Atypical task-invariant organization of multi-segment tremors in patients with Parkinson’s disease during manual tracking

“…Following progressive loss of nigrostriatal neurons, the initial symptom of PD, resting tremor, begins distally in one arm at 4-6 Hz due to altered oscillations within the pre-existing interconnection of neural networks (Beuter and Edwards, 2002;Feger, 1997). Different forms of tremulous movements can be observed in patients with PD during postural maintenance (Jankovic et al, 1999;Vaillancourt and Newell, 2000), force exertion (Forssberg et al, 2000;Vaillancourt et al, 2001), or alternate movements (Duval et al, 2004), in relation to altered central-peripheral interplay for diverse task needs (Burne, 1987;McAuley and Marsden, 2000). The presentation of kinetic tremor in PD is thought to impair task performance (Carey et al, 2002) because the temporal and amplitude controls of skilled movements could be undermined by tremor-associated muscle weakness and pacing disturbance (Brown et al, 1997;Logigian et al, 1991).…”