Enfoques teóricos que sustentan la orientación

This study demonstrated that multi-sensor kinematics quantified joint tremor amplitude to generate different tremor profiles based on the effect of paired tasks that alter limb

positioning. As literature suggests there is a peripheral component of tremor that lies within the adrenergic mechanisms in muscle spindles, this study applied task variation to understand how modulating limb positioning can influence tremor amplitude and tremor distribution in ET and PD participants.14,15 Detailed clinical examinations focusing on specific tremor features including amplitude, frequency, distribution and pattern, and associated clinical history can aid in further distinguishing between these two diseases.11 However, studies of quantitative tremor analysis involving surface EMG and accelerometry have concluded that tremor frequency ranges between ET and PD are somewhat different yet there is considerable overlap.12 Furthermore, PD and ET tremor amplitudes are similar during most positions and surface EMG studies identify patterns in PD and ET cases but these methods do not

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different limb postures has proven to be imperative in diagnostic studies as tremor features are strongly influenced by the method of measurement.13

Within ET participants, there was a significant and strong correlation of joint tremor

amplitudes, either in the wrist, elbow or shoulder, between rest tasks and between load tasks. However, this was not observed between posture tasks, a distinctive feature of ET (Figure 2- 3). Furthermore, the amplitude of wrist tremor during “posture-1” in PD was significantly higher than in ET participants, which was similar to a previous report by Jankovic in 1999.11,16 In PD participants, mean joint tremor amplitude was significantly correlated between postural and load tasks but this was not observed between rest tasks, contrasting ET (Figure 2-5). Additionally, the effect of rest task variation significantly alters PD tremor in the wrist and elbow joint, though this was not observed in ET participants. Thus, not only does the latency of tremor onset when assuming horizontal postures differentiate PD and ET tremor types,16 but also this study demonstrated that postural or rest task variations

influenced tremor amplitudes in ET or PD participants, respectively.

Burne J et alreported that PD and ET tremor amplitudes were similar in most positions.12 In accordance with past studies, mean tremor amplitudes in the wrist and elbow during tasks “posture-2”, “load-1” and “load-2” were not statistically different and were strongly correlated between ET and PD participants (Figure 2-7). It was also interesting to observe that mean wrist tremor severity during “posture-2” and in both load tasks was strongly correlated to mean elbow tremor amplitude in both ET and PD; however, a strong correlation between wrist and elbow tremor amplitudes in “posture-1” was observed in PD but not in ET. This suggested that ET may be more susceptible to peripheral reflex modification than PD tremor when the limb is held in postural positions.13

Past studies observed variation of tremor amplitude during weight-bearing tasks to distinguish between pathological tremors and physiological tremor; however the effect of

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weight-loading has not been utilized to distinguish ET and PD tremor types.11,13,17 In PD, mean elbow tremor amplitude during “rest-1” was significantly lower than in “load-1” however mean elbow tremor amplitudes in “rest-1” and “load-2” tasks were statistically similar. On the other-hand in ET, mean elbow tremor amplitude was significantly greater in “posture-2” and in both load tasks when compared to “posture-1” and both rest tasks. This emphasises that greater elbow flexion increased elbow tremor in PD and ET patients but added weight reduced elbow tremor amplitude in PD and significantly increased mean elbow tremor amplitude in ET. Interestingly the increase in ET elbow tremor during “load-2” was not accompanied by a significant increase in wrist tremor however this was not the case for PD participants. Thus, this demonstrated that tremor amplitude in ET was more sensitive to the effects of change to the mechanical state of the limb.17

In both PD and ET participants, there was a significant change in the amount of tremor originating in the F/E DOF due to task variation (between paired tasks). In addition to change in percent contribution from the F/E DOF, a significant reduction in wrist tremor originating in the R/U DOF was observed in PD between postural tasks. A possible explanation to the significant change seen in F/E DOF as opposed to P/S DOF may be due to the greater use of wrist extensors/flexors during tasks such as: assuming palms facing downwards with arms outstretched in “posture-1”, gripping a weighted cup close to chest in “load-2”, and restricted wrist extensor range of motion in “rest-1” task. The analysis of the percent contribution of tremor was not considered a distinctive element of PD or ET and hence may not be

diagnostically useful in the clinic setting. However, such joint tremor segmentation would be advantageous for individualizing focal therapy of tremor with BoNT-A injections.10 In addition, this study concluded that the segmentation of shoulder tremor would also be beneficial for BoNT-A therapy as shoulder tremor analysis cannot be used to distinguish between ET and PD tremor types.