Disorganized somatotopy in the putamen of patients with focal hand dystonia

Objective: To explore the selectivity of neuronal somatotopic representation in the striatum of patients with unilateral task-specific dystonia of the right arm. Materials and Methods: The authors used fMRI in 14 right-handed dystonic subjects to examine putaminal organization. Subjects performed flexion/extension of the right and left fingers and toes, and contraction of the lips. Results: Compared to healthy volunteer subjects, dystonic subjects had altered somatotopic organization in the left putamen, contralateral to the affected hand. Disease severity correlated with underactivation and decreased distance between right hand and lip representations. In the right putamen, ipsilateral to the affected hand, the somatotopic organization was not altered but disease severity also correlated with reduced distances between limbs. Conclusion: In dystonia there may be a dedifferentiation of the normally segregated cortico-subcortical sensorimotor maps in the putamen, which may contribute to the loss of functional selectivity of muscle activity observed in these dystonic subjects.