Dystonia is an
involuntary movement disorder characterized by muscle contractions causing abnormal postures and
spasms, affecting part or all of the body.
Dystonia may be primary where an abnormal gene, most commonly
DYT1, may be identified, or secondary to structural brain lesions or heredodegenerative disorders. The underlying defect is believed to be abnormal basal ganglia modulation of cortical motor pathways, and various motor and sensory physiological abnormalities have been demonstrated. The failure of medical treatment in many patients with the more severe and generalized forms of
dystonia has led to renewed interest in neurosurgical treatment approaches. In recent years,
deep brain stimulation (DBS) of globus pallidus internus (GPi) has emerged as an effective treatment for
dystonia, particularly patients with primary generalized
dystonia, where remarkable improvement may occur. In contrast to
Parkinson's disease, the beneficial effects of DBS in
dystonia are not immediate but progressive over weeks to months. Physiological and imaging studies in
dystonia patients with GPi DBS have demonstrated both short and long-term effects of GPi DBS on motor cortex and subcortical circuits including progressive normalization of spinal and brainstem excitability after GPi DBS which correlate with clinical improvement. These effects, in light of existing physiological data in
dystonia, suggest that GPi DBS acts primarily by major modification of basal ganglia output to brainstem, thalamus, and cortex resulting in neural reorganization, which may explain the characteristic progressive improvement in
dystonia after GPi DBS.