Focal hand dystonia: Individualized intervention with repeated application of repetitive transcranial magnetic stimulation

Objectives To examine for individual factors that may predict response to inhibitory repetitive transcranial magnetic stimulation (rTMS) in focal hand dystonia (FHD); to present the method for determining optimal stimulation to increase inhibition in a given patient; and to examine individual responses to prolonged intervention. Design Single-subject design to determine optimal parameters to increase inhibition for a given subject and to use the selected parameters once per week for 6 weeks, with 1-week follow-up, to determine response. Setting Clinical research laboratory. Participants A volunteer sample of subjects with FHD (N=2). One participant had transcranial magnetic stimulation responses indicating impaired inhibition, and the other had responses within normative limits. Interventions There were 1200 pulses of 1-Hz rTMS delivered using 4 different stimulation sites/intensity combinations: primary motor cortex at 90% or 110% of resting motor threshold (RMT) and dorsal premotor cortex (PMd) at 90% or 110% of RMT. The parameters producing the greatest within-session increase in cortical silent period (CSP) duration were then used as the intervention. Main Outcome Measures Response variables included handwriting pressure and velocity, subjective symptom rating, CSP, and short latency intracortical inhibition and facilitation. Results The individual with baseline transcranial magnetic stimulation responses indicating impaired inhibition responded favorably to the repeated intervention, with reduced handwriting force, an increase in the CSP, and subjective report of moderate symptom improvement at 1-week follow-up. The individual with normative baseline responses failed to respond to the intervention. In both subjects, 90% of RMT to the PMd produced the greatest lengthening of the CSP and was used as the intervention. Conclusions An individualized understanding of neurophysiological measures can be an indicator of responsiveness to inhibitory rTMS in focal dystonia, with further work needed to determine likely responders versus nonresponders.