Focal dystonia following soft tissue injury: three case reports with long-term outcome

Three cases of focal dystonia are described which followed upper extremity injuries. Each patient developed a dystonic posturing in that limb; two patients improved when their initial condition was addressed. Various authors have proposed that focal dystonia represents a limited form of generalized dystonia, which is believed to result from a disturbance of striatopallidal-thalamic input to the supplementary motor area (SMA)--a vital executive area for motor control. An alternative hypothesis is offered; that is, a similar dysfunction of the SMA could be the result of altered sensory information from a painful limb disturbing the crucial integration between sensory input and motor performance. The following three examples of such integration are provided: (1) the long loop or transcortical reflex, (2) input of distinctive somatosensory neurons to the SMA, and (3) the projection of proprioceptive and tactile sensory input into peripheral receptive fields of the motor cortex.