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Dystonia refers to involuntary, sustained contraction of limb, truncal, or cranial muscles. Dystonia may be idiopathic, as in Primary Dystonia or secondary to brain, spinal cord, or nerve injury. Cerebral palsy is the commonest etiology. Movement and stress serve as triggers in dystonic patients, whereas sleep and gentle touch alleviate their symptoms. Several neurosurgical options are available following the failure of oral medication and botulin toxin injection. These include intrathecal baclofen, deep brain stimulation, and peripheral denervation.
Co-contraction of agonist and antagonist muscles produces characteristic postures in dystonic patients, which must be distinguished from spasticity, choreoathetosis, and essential tremor. Dystonic movements are slow yet forceful, expending a considerable amount of energy that often leaves patients underweight. Primary dystonia usually presents in adulthood and remains localized, affecting the neck (torticollis), face (blepharospasm), jaw, vocal cord, or arm (writer’s cramp) muscles. Irregular tremor can accompany muscle spasm in these patients. Primary dystonia may follow an autosomal dominant inheritance pattern with incomplete penetranceBrain MR in secondary dytonia may show injury to the basal ganglia, but is normal in the primary idiopathic variant. Secondary causes are often accompanied by other parkinsonian features. Trauma, hypoxia, stoke, tumor, toxins, excessive dopaminergic medication, and heredodegenerative diseases such as Huntington’s, Wilson’s, and Lesch-Nyhan are some known etiologies. Psychotic patients may also contract their muscles in a pattern mimicking dystonia. Severity of disease and response to treatment may be assessed with the Barry-Albright Dystonia Scale.
Childhood-onset dystonia may respond to dopamine (Seqawa’s disease), which proves less effective in adults. In many cases other oral therapies are also inadequate, including baclofen, benzodiazepines, barbiturates, anti-psychotics, beta-blockers, and anti-epileptics. In patients failing oral medications, intrathecal baclofen via an implanted pump has proven highly successful in relieving some symptoms. Deep brain stimulation or lesioning is more effective for primary than secondary dystonia. Neck, trunk and axial involvement usually requires bilateral targeting of either the thalamus or globus pallidus. Peripheral nerve destruction may prove beneficial for torticollis, although other forms of dystonia involve too many muscle groups to safely denervate. Cerebellar and dorsal column stimulation have not proven to be effective treatments.
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- Albright AL, Barry MJ, Fasick P, et al: Continuous Intrathecal Baclofen Infusion for Symptomatic Generalized Dystonia. Neurosurgery 38: 934-939, 1996.