Dystonia
Sustained muscle contractions, frequently cause twisting repetitive movements or abnormal postures (see also Chapter 9). Also called “torsion dystonia.” Movements sometimes rhythmic (dystonic tremor).
EMG in dystonia: simultaneous contraction of agonist and antagonist muscles with prolonged bursts and overflow to extraneous muscles.
Definitions
Task-specific dystonia: movements and postures elicited by specific actions. Action dystonia: Evoked by any action of involved body part. Overflow dystonia: evoked by action of other body parts. Sensory trick: simple touch diminishes dystonic movement (touching chin or side of face reduces torticollis).
Focal dystonia: single area affected. Segmental: two or more contiguous body parts. Generalized: involves leg plus some other area. Multifocal: two or more noncontiguous parts. Hemidystonia: half-body.
Classification of Dystonia
See Table 113.1. Age at onset: most important prognostic factor for primary dystonia; younger onset, more likely dystonia later becomes severe and spreads to other body parts.
Onset of dystonia in leg second predictor of more rapid progression course. Adult-onset dystonia more often focal than generalized.
Table 113.1 Classifications of Torsion Dystonia | |||
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Table 113.2 Gene Nomenclature for the Dystonias | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Primary Torsion Dystonias
Restricted to dystonic postures and movements; sometimes tremor. Include familial and sporadic conditions. See Table 113.2.
Oppenheim (DYT1) Dystonia
Onset in childhood or adolescence in leg (most patients) or arm, then neck or larynx. Mean onset age 13 years; rarely after 26.
Progresses to generalized or multifocal dystonia in 65% of all patients. Probability of progression higher with onset in childhood and in leg. Rate of progression varies; mostly in first 5 to 10 years.
Mutation in DYT1 gene; chromosome 9. Autosomal dominant, but penetrance 30% to 40%, highly variable. Phenotype
expression also highly variable. Gene product: torsin-A, a heat-shock protein.
expression also highly variable. Gene product: torsin-A, a heat-shock protein.
Affects most ethnic groups. Accounts for great majority of childhood and adolescent-onset primary dystonia in Ashkenazi Jews, about 30% to 50% in non-Jews. Higher frequency in Ashkenazi Jews due to founder effect.
Genetic testing for DYT1 mutation: indicated for any primary dystonia starting before age 26. Counseling especially important given highly variable penetrance, phenotype.
Other Early-Onset Non-DYT1 Primary Dystonias
DYT6 dystonia: autosomal dominant; onset in childhood or adulthood. Disabling dysphonia, dysarthria. Especially in Amish/Mennonite population.
DYT13 dystonia: described in one Italian family. Autosomal dominant. Jerking movements of neck, shoulder; variable spread to cranial and brachial muscles. Mild disability in most.
Adult Onset Primary Dystonia
DYT7 dystonia: predominantly cervical; northwest Germany.Related posts:
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