Shortened cortical silent period in adductor spasmodic dysphonia: evidence for widespread cortical excitability

Abstract

The purpose of this study was to compare cortical inhibition in the hand region of the primary motor cortex between subjects with focal hand dystonia (FHD), adductor spasmodic dysphonia (AdSD), and healthy controls. Data from 28 subjects were analyzed (FHD n=11, 53.25 ± 8.74 y; AdSD: n=8, 56.38 ± 7.5 y; and healthy controls: n=941.67 ± 10.85 y). All subjects received single pulse TMS to the left motor cortex to measure cortical silent period (CSP) in the right first dorsal interosseus (FDI) muscle. Duration of the CSP was measured and compared across groups. A one-way ANCOVA with age as a covariate revealed a significant group effect (p<0.001). Post hoc analysis revealed significantly longer CSP duration in the healthy group vs. AdSD group (p<0.001) and FHD group (p<0.001). These results suggest impaired intracortical inhibition is a neurophysiologic characteristic of FHD and AdSD. In addition, the shortened CSP in AdSD provides evidence to support a widespread decrease in cortical inhibition in areas of the motor cortex that represent an asymptomatic region of the body. These findings may inform future investigations of differential diagnosis as well as alternative treatments for focal dystonias.

Keywords: Adductor spasmodic dysphonia; Cortical silent period; Focal hand dystonia; Transcranial magnetic stimulation.

Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Figures

Fig. 1.

Sample of a single cortical silent period EMG trace in first dorsal interosseus of a healthy subject.

Fig. 2.

Mean (SD) duration of cortical silent period of first dorsal interosseus in healthy, adductor spasmodic dysphonia (AdSD) and focal hand dystonia (FHD) (*p < 0.001; **p = 0.045).