Hyperkinetic Movement Disorder: Idiopathic Torsion Dystonia

Other genetic mutations causing childhood-onset generalized dystonia have been described more recently. Next to DYT1, perhaps the most important is DYT6, which is associated with a mutation in the THAP1 gene.

Adult-onset primary dystonia is usually focal or segmental in distribution and may be a forme fruste of idiopathic generalized dystonia. It may develop in susceptible individuals who perform repetitive tasks, such as instrumentalists, typists, dental hygienists, and writers, or it may appear without known precipitating factors. Examples of focal dystonia are writer’s cramp, cervical dystonia (spasmodic torticollis), blepharospasm (bilateral, involuntary, synchronous, forceful eye closure), oromandibular dystonia (forceful involuntary jaw opening or closure), spasmodic dysphonia (adductor or abductor dysphonia), and musician’s dystonia. In segmental dystonia, characteristically there is involvement of two or more adjacent body parts. Hemidystonia involves an arm and leg on the same side of the body. Axial dystonia affects midline structures (trunk and neck muscles) and may cause speech and swallowing difficulty or arching of the back or neck. Multifocal dystonia refers to abnormal posturing affecting two or more nonadjacent body parts. Involvement of both legs and at least one arm, or axial involvement in combination with at least one affected limb is usually observed in generalized dystonia. Deep tendon reflexes may be normal or exaggerated, particularly in patients with a secondary cause or in patients with cervical dystonia who developed a compressive myelopathy as a consequence of severe and often early degenerative spine disease. In some patients, a “dystonic tremor” or myorrhythmia may be noted.

In secondary dystonias, a cause is identified, such as cerebral infarction, tumors, brain trauma, infections, and medication exposure, particularly to dopamine-blocking agents (neuroleptics, metoclopramide). Secondary dystonia can be focal, likely contralateral to the lesion, or may be due to minor peripheral trauma such as that resulting from the severe causalgia-dystonia syndrome. It may be hemidystonic or segmental when two or more contiguous body parts are affected, or generalized when the trunk and two other contiguous body parts are involved. Secondary generalized dystonia may result from trivial trauma or, in the appropriate setting, psychogenic factors may be the sole cause. Dopamine receptor–blocking medications, such as neuroleptics and phenothiazine-based antiemetics, can produce acute dystonia after a single dose or tardive dystonia after chronic usage.

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