(See also Overview of Movement and Cerebellar Disorders.)
Dystonia may be
CNS disorders that can cause dystonias include
Drugs that most commonly cause dystonias include
Dystonia may resemble athetosis and choreoathetosis and should be distinguished from them because etiology and management may differ.
Dystonias are classified based on
Etiology is categorized as
Clinical features include the following:
Onset: Can occur at any age, from infancy to late adulthood
Body distribution: May be focal (limited to one body part), segmental (involving ≥ 2 more contiguous body parts, such as the upper and lower face or face and neck), multifocal (involving ≥ 2 noncontiguous body parts, such as the neck and leg), generalized (involving the trunk plus 2 different body parts), or hemicorporal (involving half the body; also called hemidystonia)
Temporal pattern: May be static, progressive, paroxysmal, or persistent and may have diurnal variability or be triggered by certain tasks (task-specific dystonia)
Isolated (no evidence of another movement disorder) or combined (accompanied by other involuntary movements [other than tremor], but predominantly dystonia)
Cervical dystonia (spasmodic torticollis)—involuntary contractions of the neck muscles—is the most common dystonia.
Generalized dystonia may be inherited or secondary to another disorder or drug.
This rare dystonia is progressive and characterized by sustained, often bizarre postures. It is often inherited as an autosomal dominant disorder with partial penetrance due to mutations in the DYT1 gene; in some family members, the gene is minimally expressed. For example, some carriers have no symptoms (a forme fruste of the disorder) or only dystonic tremor.
Symptoms of primary generalized dystonia usually begin in childhood with inversion and plantar flexion of the foot while walking. At first, the dystonia may affect only the trunk or leg but often progresses to affect the whole body, usually moving cephalad. Patients with the most severe form may become twisted into grotesque, nearly fixed postures and ultimately be confined to a wheelchair. Symptoms that begin during adulthood usually affect only the face or arms.
Mental function is usually preserved.
This rare dystonia (also called Segawa disease) is inherited as an autosomal dominant (DYT5a, GTP cyclohydrolase 1 gene [GTPCH1]) disorder or an autosomal recessive (DYT5b) disorder (tyrosine hydroxylase deficiency).
Symptoms of dopa-responsive dystonia usually begin during childhood. Typically, one leg is affected first. As a result, children tend to walk on tiptoes. Symptoms worsen at night. Walking becomes progressively more difficult, and arms and legs are affected. However, some children have only mild symptoms, such as muscle cramps after exercise. Sometimes symptoms appear later in life and resemble those of Parkinson disease. Movements may be slow, balance may be difficult to maintain, and a tremor may occur in the hands during rest.
Symptoms lessen dramatically when low doses of levodopa are used. If levodopa relieves the symptoms, the diagnosis is confirmed.
Focal dystonias affect a single body part. They typically start during adulthood, after age 20 to 30 years.
Initially, the posturing may be intermittent or task-specific (and thus is sometimes described as spasms). The movements tend to be more prominent during action and less so at rest, but these differences lessen over time, often resulting in distortion of the affected body part and severe disability. However, pain is uncommon except in focal primary dystonia of the neck (cervical dystonia) and in the dystonias that occur when response to levodopa starts to wear off in Parkinson disease (most often affecting the lower limb, eg, causing inversion of the foot).
Occupational dystonia consists of task-specific focal dystonic spasms triggered by performing skilled acts (eg, writer’s cramp, musician´s dystonia, the yips in golfers).
Spasmodic dysphonia consists of a strained, hoarse, or creaky voice due to focal dystonia of the laryngeal muscles.
Cervical dystonia manifests with involuntary tonic contractions or intermittent spasms of neck muscles. It has two forms:
The caput form (torticaput) involves muscles that move the skull or head joints; it is further described as anterocaput, laterocaput, or retrocaput. The collis form involves muscles that control the lower cervical vertebrae and is further described as anterocollis, laterocollis, retrocollis, or torticollis.
These dystonias affect ≥ 2 contiguous body parts.
Meige syndrome (blepharospasm plus oromandibular dystonia) consists of involuntary blinking, jaw grinding, and grimacing, usually beginning during late adulthood. It must be distinguished from the buccal-lingual-facial chorea of tardive dyskinesia and tardive dystonia (a variant of tardive dyskinesia).
For generalized dystonia, an anticholinergic drug (trihexyphenidyl 2 to 10 mg orally 3 times a day, benztropine 3 to 15 mg orally once a day) is most commonly used; the dose is slowly titrated to target. A muscle relaxant (usually baclofen), a benzodiazepine (eg, clonazepam), or both may provide adjunctive benefit.
Generalized dystonia that is severe or does not respond to drugs may be treated with deep brain stimulation of the globus pallidus interna (GPi), a stereotactic neurosurgical procedure. In some cases, stereotactic unilateral ablative surgery of the GPi is indicated.
For focal or segmental dystonias or for generalized dystonia that affects mainly one body part, the treatment of choice is
Botulinum toxin weakens excessive muscular contractions through chemodenervation, but it does not alter the abnormal brain circuitry that causes dystonia. Toxin injection is most effective for blepharospasm and torticollis but can be very effective for most other forms of focal dystonia. Dosage varies greatly. Treatments must be repeated every 3 to 4 months because the toxin's duration of activity is limited. Repeating injections before the 3 months have elapsed may cause antibodies against botulinum toxin to develop and thus lessen the toxin's benefit. In some patients, repeated injections, even with dosing intervals > 3 months, cause antibodies against the toxin to develop. However, not all of these antibodies neutralize botulinum toxin.
Dystonias cause abnormal postures and/or twisting, jerky movements.
Focal dystonias are common and usually begin during adulthood.
Generalized dystonia may be inherited or secondary to another disorder or a drug.
Diagnosis is clinical.
Treat generalized dystonias with anticholinergic drugs and/or muscle relaxants; treat focal or segmental dystonias and generalized dystonias that affect mainly one body part with botulinum toxin injections.