What is dystonia?

Dystonia is a neurologic movement disorder dominated by involuntary,
sustained or repetitive, patterned muscle contractions or spasms,
frequently causing squeezing, twisting, and other movements or
abnormal postures. Typically, dystonia begins in a single body part
(focal dystonia), such as the hand, neck or eyelids, and then it
spreads to adjacent body parts (segmental dystonia). Blepharospasm, a
focal dystonia manifested by an involuntary eye closure produced by
spasmodic contractions of the eyelids and eyebrows, is often
associated with dystonic movements of facial, jaw, laryngeal, and
neck muscles. Oromandibular dystonia may be manifested by involuntary
jaw opening or closing associated with clenching (trismus) and teeth
grinding (bruxism), which may lead to secondary dental wear and
temporal-mandibular joint (TMJ) syndrome. In our Movement Disorders
Clinic at Baylor College of Medicine, neck or cervical dystonia is
clearly the most frequent form of dystonia. This form of focal
dystonia is characterized by patterned (same group of muscles),
repetitive, head movements or more sustained abnormal postures of the
head. The term "spasmodic torticollis" is still occasionally used to
describe this form of dystonia. However, since it is not always
spasmodic and it does not always consist of head turning
(torticollis), the term "cervical dystonia" is preferred as a generic
descriptor of dystonic movements or postures involving the neck. In
addition to torticollis (turning of the head), cervical dystonia may
be manifested by neck flexion (anterocollis), extension
(retrocollis), or head tilt (laterocollis). In approximately a third
of all patients, cervical dystonia progresses to involve contiguous
body parts such as the oromandibular region, shoulder, trunk, and
arm. Cervical dystonia is associated with pain in about 75% of
patients and most patients have discovered certain maneuvers
or "tricks", such as touching the chin or neck, to correct the
abnormal postures. Segmental dystonia involving eyelids
(blepharospasm) and other facial, jaw (oromandibular) and neck
(cervical) muscles is still sometimes referred to as "Meige's
syndrome", but the term "cranial-cervical dystonia" is preferred
because it more accurately describes the anatomical distribution of
the dystonic movements. Spasmodic dysphonia, a focal dystonia of the
vocal cords and larynx, is characterized by strained, effortfull
voice interrupted by uncontrollable pitch breaks or voiceless pauses
(adductor spasmodic dysphonia) or whispering, breathy voice (abductor
spasmodic dysphonia).

While cervical dystonia is the most common form of dystonia
encountered in a specialized clinic, writer's cramp is probably more
common in general population. In addition to this "task-specific"
dystonia, there are many other examples of occupational dystonias
affecting the performance of musicians, sportsmen, and others whose
skills depend on finely coordinated movements. Dystonia, particularly
of childhood onset, may spread to involve the legs, trunk and other
body parts (generalized dystonia). Unilateral dystonia, confined to
only one half of the body, is referred to as hemidystonia. In
contrast to focal and segmental dystonia, which is
usually "idiopathic" or "primary" (no specific cause except possibly
genetic), majority of patients with hemidystonia have an identifiable
etiology such as head trauma, stroke, arteriovenous malformation,
tumor, encephalitis or other pathology affecting the opposite basal
ganglia.

Primary dystonias are often due to genetic abnormalities. The most
common form of genetic, childhood-onset dystonia is the so-called
DYT1 dystonia. This dystonia, which occurs with unusual frequency in
Ashkenazi Jewish population, is manifested by onset of writer's
cramp, foot inversion, or other dystonia of the limbs, typically
before the age of 10, and progressive to more generalized dystonia
involving legs, arms and trunk. Although the progression may vary
between individuals of the same or different families, many children
with DYT1 dystonia require assistance with ambulation by the time
they reach early teens. The diagnosis of DYT1 dystonia can be
confirmed by a genetic DNA test (see below).

What causes dystonia?
Although in most patients with dystonia no specific abnormality or
lesion can be identified by neuroimaging or even autopsy studies,
there is convincing evidence that this movement disorder is due to
abnormal function of the deep portion of the brain, called basal
ganglia. The most important advance in our quest to understand the
cause of dystonia has been the identification of a gene, called DYT1
on chromosome 9, the mutation of which causes primary dystonia. The
DYT1 gene codes for the protein TorsinA which accumulates abnormally
in selected neurons of the brainstem. It is not yet known, however,
how this abnormality leads to dystonia. Besides DYT1, there are many
other genetic forms of dystonia, and new gene abnormalities are being
added to the growing list of genetic forms of dystonia.

Not all dystonias, however, are of genetic origin; some are sporadic
(no family history) and others are secondary to some specific causes
such as certain metabolic and neurodegenerative disorders (e.g.
Wilson's disease), brain injury or other lesions (e.g. cerebral
palsy), certain drugs that block dopamine receptors, and many other
causes. The dopamine receptor blocking drugs, also called
neuroleptics, such as the major tranquilizers (e.g. haloperidol) and
gastrointestinal drugs (e.g. metoclopramide) can cause not only an
acute transient dystonic reaction, but more importantly a persistent
dystonic disorder (tardive dystonia). Besides central etiologies,
which presumably account for the vast majority of dystonias,
peripherally-induced dystonia caused by an injury to the affected
body part is being increasingly recognized as an important cause of
focal and segmental dystonia. Finally, physical or emotional stress
and a variety of other psychological factors may be associated with
abnormal movements resembling dystonia, the so-called "psychogenic
dystonia".

Treatment
Despite the paucity of knowledge about causes of dystonia, the
treatment of this condition has markedly improved, largely as a
result of application of botulinum toxin (BTX). Before contemplating
BTX therapy, however, potentially curable causes of dystonia, such as
certain drug-induced dystonias or Wilson's disease, should be
considered. Physical therapy, including well fitted braces may be
helpful to some dystonic patients, but are usually unsatisfactory
when used alone. About a third of patients benefit from pharmacologic
therapy using medications such as trihexyphenidyl, baclofen,
tetrabenazine, and levodopa. Surgical techniques, such as local nerve
or muscle excision and ablation or high frequency deep brain
stimulation (DBS) have been used successfully in patients who
continue to have disabling dystonia despite optimal medical or BTX
therapies. DBS of the globus pallidus internum (GPi), has emerged as
the surgical treatment of choice in patients with severe generalized
or segmental dystonia as well as hemidystonia