Rating scales for musician's dystonia: the state of the art

Abstract

Musician's dystonia (MD) is a focal adult-onset dystonia most commonly involving the hand. It has much greater relative prevalence than non-musician's focal hand dystonias, exhibits task specificity at the level of specific musical passages, and is a particularly difficult form of dystonia to treat. For most MD patients, the diagnosis confirms the end of their music performance careers. Research on treatments and pathophysiology is contingent upon measures of motor function abnormalities. In this review, we comprehensively survey the literature to identify the rating scales used in MD and the distribution of their use. We also summarize the extent to which the scales have been evaluated for their clinical utility, including reliability, validity, sensitivity, specificity to MD, and practicality for a clinical setting. Out of 135 publications, almost half (62) included no quantitative measures of motor function. The remaining 73 studies used a variety of choices from among 10 major rating scales. Most used subjective scales involving either patient or clinician ratings. Only 25% (18) of the studies used objective scales. None of the scales has been completely and rigorously evaluated for clinical utility. Whether studies involved treatments or pathophysiologic assays, there was a heterogeneous choice of rating scales used with no clear standard. As a result, the collective interpretive value of those studies is limited because the results are confounded by measurement effects. We suggest that the development and widespread adoption of a new clinically useful rating scale is critical for accelerating basic and clinical research in MD.

Figure 1. Summary of musician's dystonia literature and categories of functional motor assessments

(A) Distribution of literature search results. “Reviews” consists of reviews, perspectives, overviews, and pedagogical material. “Other” consists of experimental studies involving no patients with musician’s dystonia. (B) Temporal distribution of experimental and review publication dates, by half-decades. (C) Among the experimental studies, proportion using qualitative only vs quantitative categories of motor function assessment. (D) Temporal distribution of quantitative and qualitative experimental study publication dates, by half-decades.

Figure 2. Rating scale use within musician's dystonia literature

Within experimental studies using quantitative motor function assessments, (A) histogram of number of scales used in each study, (B) number of studies using each type of scale (subjective by patient, subjective by clinician, objective, or combinations thereof), and (C) number of studies using each scale, grouped by type.