INTRODUCTION

Musician’s dystonia (MD) is a focal, task-specific movement disorder that affects fine motor control solely while playing an instrument [1], severely impairing musicians’ abilities and jeopardizing their careers [2,3]. The pathophysiology of MD is not fully understood, but known risk factors include genetic predisposition, physical trauma, practice behavior, and spatiotemporal constraints [2,4-10]. Epidemiological studies suggest that extrainstrumental workloads—usage of the dominant hand beyond musical performance—may significantly influence the localization of MD, possibly more than previously thought [11].

From this finding, we derived two hypotheses: 1) subjective playing ability at dystonia onset is worse when MD affects the dominant side. 2) Improvements in subjective playing ability during dystonia treatment depend on which side is affected (dominant or nondominant).

MATERIALS & METHODS

Patients

Subjects were recruited from a specialized outpatient clinic. A neurologist diagnosed the condition after excluding other movement disorders, such as Parkinson’s disease, and confirmed the criteria of primary task specificity (symptoms occurring only when playing an instrument) and context independence (symptoms occurring during practice at home and in concert situations).

The study included 151 subjects affected on the dominant side (age mean±standard deviation (SD): 49±11 years, 76% male) and 92 patients affected on the nondominant side (age mean±SD: 48±11 years, 80% male). In the dominant group, 146 were right-handed, and 5 were left-handed, whereas in the nondominant group, 84 were right-handed, and 8 were left-handed (Supplementary Table 1 in the online-only Data Supplement). Ambidextrous patients (n=18) and patients affected bilaterally (n=14), and one ambidextrous patient who was affected bilaterally (n=1) were excluded. Handedness was measured via the Edinburgh Handedness Inventory [12]. The study was approved by the ethics committee of Hanover Medical School (vote 9808_BO_K2021). Patients gave informed consent for participation according to the Declaration of Helsinki.

Questionnaire

We used a modified version of a questionnaire previously used for assessing playing ability in MD [2,13]. Patients were asked to retrospectively estimate their playing ability at dystonia onset and after treatment (i.e. when the questionnaire was completed) as a percentage of their playing ability before dystonia onset (i.e. 100% playing ability). For each patient, the delta in playing ability was calculated as the difference between playing ability after treatment and at dystonia onset. Positive and negative delta scores indicate improvements and deterioration in playing ability since dystonia onset, respectively. A translated version of the questionnaire is included as Supplementary Material (in the online-only Data Supplement).

Statistical analysis

To evaluate factors affecting the onset and progression of dystonia, we examined differences in family history, age at onset of instrumental playing, age at dystonia onset, prior injuries/pain, gender distribution, and therapies received (trihexyphenidyl, botulinum toxin, retraining). Chi-square tests were used for frequency distributions, and Wilcoxon tests were used to compare nonparametric variables. For hypotheses 1) and 2), we created a linear mixed-effects regression model, regressing playing ability on time (playing ability at dystonia onset vs. after treatment), group (dominant vs. nondominant), gender, age at dystonia onset, age of beginning to play, years since MD diagnosis, and the time:group interaction, with all variables standardized. T-test post hoc analyses were conducted, and hypothesis 2) was further assessed via a between groups t-test on delta scores.

RESULTS

There were no significant differences in age at the beginning of instrumental playing, age at dystonia onset, average practice time per year, cumulative practice time until dystonia onset, gender distribution, or positive family history of movement disorders and preceding pain or trauma between the dominant and nondominant groups. While there was no significant difference between groups regarding the proportion of those who received botulinum toxin and retraining, more participants from the nondominant group had at some point been taking trihexyphenidyl. The proportions of right- and left-handed individuals were not significantly different between the groups (χ²=2.2962, p=0.13). Moreover, in contrast to Baur et al. [11], we did not find a significant difference between the proportional frequency of right-handed and left-handed individuals in the group of patients affected on the right or left side, respectively (χ²=1.11×10^-31, p>0.99). For detailed patient characteristics are presented in Table 1, which distinguishes between the dominant and nondominant groups. Additional information on the distribution of left- and right-handed patients is provided in Supplementary Table 1 (in the online-only Data Supplement).

The linear mixed model revealed a significant main effect of time (β=11.65, p<0.05) but not of group (β=-2.31, p>0.05). There was a significant interaction effect between time and group (β=12.44, p<0.05). T-test post hoc analysis revealed a significant improvement in playing ability between dystonia onset and after treatment for the dominant group (p<0.001) but not for the nondominant group (p=0.57). At dystonia onset, the difference in playing ability between groups was not statistically significant (p=0.27). There were no significant effects of gender, MD onset, or time since diagnosis until completion of the questionnaire. A trend toward better playing ability after treatment for the dominant groups was observed (p=0.08) (Figure 1A).

The t-test revealed a significantly greater delta in playing ability for the dominant group (t=2.5, df=228, p=0.012) (Figure 1B).

DISCUSSION

The aim of this study was to assess differences in playing ability due to hand dominance and MD lateralization at dystonia onset and after treatment.

The most surprising and unexpected findings of this paper are that, contrary to our hypothesis, playing ability at dystonia onset was not significantly worse in the dominant group; second, playing ability improved over time only in the dominant group and remained unchanged in the nondominant group; and third, the overall change in playing ability was significantly greater in the dominant hand, confirming hypothesis 2. Moreover, in contrast to the previously cited study [11], we did not find any significant difference in handedness distribution between MD patients affected at the right or left side. In fact, not only right-handers but also left-handers were numerically more commonly affected on the right side; however, statistical significance was likely not reached due to the small number of left-handers.

As all patients had been seen in the same specialized outpatient clinic, they had received the same standard of care regarding offered treatments (trihexyphenidyl, botulinum toxin, retraining). The fact that more patients in dominant group than in the nondominant group had tried treatment with trihexyphenidyl clearly does not explain their poorer outcome over the course of the disease. It is therefore interesting that our results were inconsistent with the earlier findings of Baur and colleagues [11]. One possible explanation is that we assessed handedness using the Edinburgh Handedness Inventory and not, as in the cited study, based on self-reports; this is relevant insofar as we observed clear discrepancies between the self-assessments of handedness and the results of the validated handedness scale in our group.

Interestingly, while string players were exceptionally prone to MD of the left hand (66%), left-handedness was much less common in string players with MD (only 1 of 40 violinists or 2.5%) than in the general population (11%) [14]. Since other studies have already shown that left-handedness is even overrepresented in healthy string players [15], our observation could indicate that, in string players, being left-handed may actually be protective against MD. This finding implies that the greater dexterity of the dominant hand, when matched to the side exposed to greater temporospatial demands on the instrument, has a protective effect against the occurrence of dystonia. Conversely, the additional strain caused by handedness does not appear to have a negative effect.

In summary, our findings suggest that a greater extrainstrumental workload of the dominant hand does not influence which hand MD manifests itself more often, nor does it lead to worse symptoms at dystonia onset; it appears, however, to have an impact on the process of relearning motor control. From the concept of metaplasticity, it is known that “the extent of motor learning may be modulated by the history of motor cortex activity” [16]. Other studies have shown that long-term fine motor training leads to enhanced synaptic plasticity [17] and to a metaplasticity-induced increase in the efficiency of Hebbian learning [18]. It is fair to assume that the dominant hand has a greater cumulative amount of fine motor training. Since the dominant group had not received more treatments and, on the contrary, had used trihexyphenidyl even less frequently, we propose that metaplasticity-induced changes [16-19] may play a role in the efficacy of retraining measures in MD.

One limitation of this study is the subjective and retrospective assessment of playing ability by the patients. We are aware that further prospective studies that include an objective measure of playing ability, such as scale-playing analysis, are needed [13,20]. However, to our knowledge, this is one of the largest MD samples assessed thus far, and the significant differences in improvement in playing ability suggest that our results are unlikely to be attributed to recall bias or overestimation of current playing ability.

In conclusion, we found that handedness does not appear to significantly influence which side is preferentially affected by MD, nor does a greater extrainstrumental burden of the dominant hand have any negative influence on the severity of MD at the onset and over the course of MD. Conversely, greater dexterity on the more stressed side may protect against the onset of MD, which is consistent with the conspicuously small number of left-handed people in the group of string players with MD; however, this remains speculative and should be investigated further in epidemiological studies.

Supplementary Materials

Notes

Conflicts of Interest

The authors have no financial conflicts of interest.

Funding Statement

This study was funded by University of Music, Drama and Media Hannover, Germany

Acknowledgments

We want to thank everyone who participated in this study as well as Philipp Heiß and Paula Hilsendegen for helping to curate the data.

Author Contributions

Conceptualization: André Lee. Data curation: Johanna Doll-Lee, André Lee. Formal analysis: Johanna Doll-Lee, Edoardo Passarotto. Funding acquisition: André Lee, Eckart Altenmüller. Investigation: André Lee, Eckart Altenmüller. Methodology: André Lee, Johanna Doll-Lee. Project administration: André Lee. Resources: André Lee. Software: André Lee, Johanna Doll-Lee, Edoardo Passarotto. Supervision: André Lee. Validation: André Lee, Johanna Doll-Lee. Visualization: Johanna Doll-Lee, Edoardo Passarotto. Writing—original draft: Johanna Doll-Lee. Writing—review & editing: all authors.

Figure 1.

Development of playing ability according to the dominant or nondominant hand being affected. A: The dominant group (blue) showed significant improvement in playing ability (p<0.001) compared with the nondominant group (red); there was no difference at dystonia onset. A trend toward better playing ability after treatment for the dominant groups was observed (p=0.08). B: The dominant group had greater delta scores (p=0.012). The error bars indicate the standard error.

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Figure & Data

References

Citations

Citations to this article as recorded by  

• Aufgabenspezifische Dystonie und Tremor: Therapeutische Konzepte für neurologische Ausfälle bei Musikern
  Johanna Doll-Lee, Till-Alexander Plinkert, André Lee
  Deutsches Ärzteblatt Online.2025;[Epub]     CrossRef

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