Dystonia, a term first used by Oppenheim in 1911, is a motor syndrome of sustained involuntary muscle contractions causing twisting and repetitive movements, sometimes tremor, and/or abnormal postures. Dystonic movements may initially appear with voluntary movement of the affected part ("action dystonia") but may eventually occur with voluntary movement elsewhere in the body ("overflow"). The severity of dystonia may be reduced by sensory tricks (geste antagoniste), using tactile or proprioceptive stimuli to lessen or eliminate posturing; this feature is unique to dystonia. Dystonia may develop after muscle fatiguing activity, and patients with focal dystonias show more rapid fatigue than normals.
Dystonic disorders may be classified according to:
- Age of onset: the most significant predictor of prognosis: worse with earlier onset;
- Distribution: focal, segmental, multifocal, generalized, hemidystonia;
- Etiology: primary/idiopathic vs. secondary/symptomatic.
Primary/idiopathic dystonias include:
- Primary torsion dystonia (idiopathic torsion dystonia)
- Severe generalized dystonia (dystonia musculorum deformans)
- Segmental, multifocal and focal dystonias (e.g., torticollis, blepharospasm, writer’s cramp)
- Dopa-responsive dystonia (DRD; Segawa’s syndrome)
- Myoclonic dystonia
- The differential diagnosis is broad (more than 40 known causes), including:
- Heredodegenerative disorders: Wilson’s disease, Huntington’s disease, Hallervorden-Spatz disease, mitochondrial disorders, X- linked dystonia-parkinsonism (lubag)
- Paroxysmal dystonias/dyskinesias: paroxysmal kinesigenic choreoathetosis/dystonia (PKC; usually responds to carbamazepine), and paroxysmal nonkinesigenic dystonia/choreoathetosis (PDC; does not respond to carbamazepine)
- Metachromatic leukodystrophy
- Gangliosidoses (GM1, GM2)
- Perinatal cerebral injury
- Head trauma
- Multiple sclerosis
- Drugs/toxins, e.g., antipsychotic, antiemetic, and antidepressant drugs
Appropriate investigations to exclude these symptomatic causes (especially Wilson’s disease) are appropriate.
The pathogenesis of dystonia is poorly understood. Different mechanism may apply in different conditions. Peripheral focal dystonias, such as torticollis and writer’s cramp, have been suggested to result from abnormal afferent information relayed from "stiff " muscle spindles. The genetic characterization of various dystonic syndromes may facilitate understanding of pathogenesis.
From a therapeutic point of view, one of the key questions relates to response to levodopa: dopa-responsive dystonia (DRD) responds very well to levodopa (and response fluctuations do not develop over time; cf. Parkinson’s disease). Other treatments which are sometimes helpful include anticholinergics, dopamine antagonists, dopamine agonists, and baclofen. Drug-induced dystonia following antipsychotic, antiemetic, or antidepressant drugs is often relieved within 20 minutes by intramuscular biperiden (5 mg) or procyclidine (5 mg). Botulinum toxin may be very helpful in some focal dystonias (e.g., blepharospasm). Surgery for dystonia using deep brain stimulation is still at the experimental stage.
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