Sensory integration in writer's cramp: comparison with controls and evaluation of botulinum toxin effect

Abnormal temporal and spatial sensory integration have been described in mixed groups of dystonic patients. We tested somatosensory integration and the effect of botulinum toxin (BoNT) in patients with writer's cramp (WC).

Median and ulnar SEPs were recorded in 29 WC patients and in 10 controls. We performed: individual and simultaneous stimulation of median and ulnar nerves (MU) and paired stimulation of median nerve at interstimulus-interval (ISI) of 40 and 100 ms. All the trials were repeated after blinded randomized treatment with placebo or BoNT-A.

We found no differences between patients and controls in standard SEPs. Spatial (except for N9) and temporal suppression after ISI 40 were present in both groups for all the waves; after ISI 100, suppression was present only for N70. There were no differences between patients and controls. After BoNT-A treatment, no changes were observed.

In contrast with previous findings in heterogeneous dystonic groups, and although some studies suggest impairment of spatial and temporal sensory discrimination in patients with focal dystonia, in our large cohort of patients with WC we found no evidence of abnormal somatosensory integration investigated by means of SEPs and no changes in somatosensory variables after BoNT-A treatment.

Our findings may suggest pathophysiological differences between focal and generalized dystonia, and may also point to an inferior sensitivity of SEPs in detecting abnormalities in sensory discrimination as compared to methods based on subjective discrimination.