A New Method for Quantification of Musician's Dystonia: The Frequency of Abnormal Movements Scale

Abstract

There is currently, no validated objective method available for the quantification of musicians dystonia applicable to different types of instrumentalists. To address this issue, we developed the Frequency of Abnormal Movements (FAM) scale and assessed its intra- and inter-rater correlation and concordance, internal consistency, and responsiveness. We also compared the FAM scale to the arm dystonia disability scale (ADDS) and Burke-Fahn- Marsden (BFM) scale. Eighteen patients with musicians dystonia were videotaped playing their instruments before and after sensory motor retuning therapy. Two raters, blinded to the order of the randomized video segments, independently rated each segment using the FAM, ADDS, and BFM scales. Intra-rater correlation (intraclass correlation coefficient [ICC] = 0.92, Spearmans rho = 0.87), concordance (weighted kappa = 0.76), and internal consistency (Cronbachs a = 0.96) for the FAM scale were good. Inter-rater correlation and concordance were better for the FAM scale (weighted k = 0.94, ICC = 0.96, Spearmans rho = 0.90) than for the ADDS or BFM scales (weighted k = 0.56-0.57, ICC scale = 0.81-0.82, Spearmans a = 0.68-0.76). The decrease in the FAM after 1 week of sensory motor retuning therapy was less likely to be due to chance (p = 0.06) than the decrease in the ADDS or BFM scales (p = 0.21-0.53). The FAM scale may be useful for clinical and research evaluations of patients with musicians dystonia.