Pre-movement gating of somatosensory evoked potentials in Segawa disease

Segawa disease (SD), an autosomal dominant dopa-responsive dystonia with marked diurnal fluctuation, can be clinically classified into the postural dystonia type (SD-P) and action dystonia type (SD-A). Compared to SD-A, SD-P has an earlier onset and is characterized by postural dystonia. In SD-A, along with postural dystonia, dystonic movements appear in late childhood. To evaluate the differences between these two types of SD, we studied the gating of SEPs, which is useful to investigate sensory-motor integration and might be one of the methods to detect the thalamo-cortical involvement.

Fourteen patients with SD (11-63 years) and 18 age-matched normal subjects (11-51 years) were studied. Among the 14 patients with SD, 8 patients had SD-P and 6 had SD-A. Using median nerve stimulation at the wrist, the amplitude of the frontal N30 (FrN30) was compared between pre-movement and rest conditions.

We found that the amplitude of the contralateral FrN30 was attenuated before movement in normal controls and in the majority of both SD types. On the other hand, the pre-movement-rest amplitude ratio in patients with SD-A was significantly larger than in patients with SD-P (P=0.0025). No significant differences were observed in the pre-movement-rest ratio between SD-P and normal subjects.

The preservation or impairment of pre-movement gating shown here suggests a physiological difference between the two types of SD. More specifically, sensorimotor integration of the basal ganglia-thalamo-cortical circuits may be intact in SD-P, but are affected in SD-A. We discuss the different pathophysiology seen in the different phenotype of SD based on the different developmental involvement in the basal ganglia.