Longitudinal evaluations of somatosensory-motor inhibition in Dopa-responsive dystonia

GCH1 mutations have been linked to decreased striatal dopamine and development of dopa-responsive dystonia (DRD) and Parkinsonism. Sensory and sensorimotor integration impairments have been documented in various forms of dystonia. DRD patients with confirmed GCH1 mutations have demonstrated normal short-latency afferent inhibition (SAI), a measure of sensorimotor inhibition, under chronic dopaminergic replacement therapy (DRT), but reduced inhibition after a single l-dopa dose following 24 h withdrawal. Studies have revealed normal SAI in other forms of dystonia but reductions with DRT in Parkinson's disease. Longitudinal changes in sensorimotor inhibition are unknown.

We analyzed sensorimotor inhibition using two different measures: SAI and somatosensory-motor inhibition using dual-site transcranial magnetic stimulation (ds-TMS). SAI was measured using digit stimulation 25 ms prior to contralateral primary motor cortex (M1) TMS. DS-TMS was measured using TMS over the somatosensory cortex 1 or 2.5 ms prior to ipsilateral M1 stimulation. A total of 20 GCH1 mutation carriers and 20 age-matched controls were included in the study. SAI and ds-TMS were evaluated in GCH1 mutation carriers both OFF and ON DRT compared to controls. Furthermore, longitudinal changes of SAI were examined in a subset of the same individuals that were measured ∼five years earlier.

Neither SAI nor ds-TMS were significantly different in GCH1 mutation carriers relative to controls. No effects of DRT on SAI or ds-TMS were seen but SAI decreased over time in mutation carriers OFF DRT.

Our longitudinal results suggest changes in SAI that could be associated with plasticity changes in sensorimotor networks.