Neuromuscular incoordination in musician's dystonia

The present study aims to define patterns of muscular activities specific to focal task-specific dystonia (FTSD), and classify them according to their association with the degradation of fine motor control or compensation for it.

While thirteen pianists with FTSD and ten expert pianists played several melodies on the piano, the activity of eight intrinsic and extrinsic finger muscles and the key-striking movements were recorded. To exclude the confounding effects of expertise, twelve amateur pianists also participated. The muscular activities were analyzed with a non-negative matrix factorization, an unsupervised classification technique, and multiple regression analysis.

Six different patterns of muscular coordination were identified, each of which was responsible for the keystroke with each of the five digits and co-contraction between an antagonistic pair of finger muscles. A comparison between the healthy pianists and pianists with FTSD found no evidence of FTSD-related elevation of the co-contraction. A regression analysis between the muscular coordination and the key-striking movements further identified 23.4% and 20.8% of the FTSD-related changes in the muscular activity as associated with the movement degradation (i.e. delayed transition of the finger motion from flexion to extension) and compensation for it, respectively. The former was associated not only with hyper-activation of the flexor, but also with reduced-activation of the extensor.

The present study specified neuromuscular maladaptation relevant to the FTSD symptom, which suggests that muscular incoordination rather than muscular co-contraction characterizes pathological feature of FTSD in musicians.