Current concepts of focal dystonia suggest a generalized deficit of sensorimotor integration.
If such a concept holds true, impaired central processing of sensory information should
be evident for a wide range of movements and not limited to the affected body part
in focal dystonia.
Reaching for and grasping an object depends on accurate processing and integration
of visual and somatosensory information related to intrinsic object properties. We
investigated sensorimotor integration during the performance of reach-to-grasp movements
in subjects with blepharospasm and torticollis.
The kinematics of hand transport and grasp formation when reaching for and grasping
cubes of different size were investigated in 7 subjects with blepharospasm, 7 subjects
with torticollis and 7 healthy control subjects.
Compared to healthy subjects, patients scaled peak grasp aperture accurately to object
size and the timing of peak grasp aperture in relation to the time of hand transport
did not differ between patients and controls. However, patients produced longer movement
times and smaller peak velocities of hand transport in comparison to healthy subjects.
The prolongation of movement times and the slowing of hand transport were significantly
correlated with clinical symptom severity as rated by the Unified Dystonia Rating
Scale.
Our data indicate a slowing of hand transport, but unaffected grasp formation during
reach-to-grasp movements in focal dystonia of the face and neck. Given the correlation
with clinical measures of disease severity, the slowing of hand transport may reflect
a strategic response of the motor apparatus and not a direct reflection of the underlying
pathology. We interpret the finding of unimpaired grasp formation as evidence that
there is not a general impairment of sensorimotor integration in focal dystonia.
