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Dystonia

Dystonia

Definition

Dystonia is a disabling movement disorder characterized by sustained contraction of muscles leading to twisting distorted postures. Dystonia may affect various parts of the body and has multiple causes, making classification and diagnosis challenging. The etiology behind the various forms of dystonia is unknown, although abnormal functioning of the cerebral cortex and basal ganglia and other pathways involved in movement are presumed. Clinical and basic science research on humans and primates, and identification of multiple genes causing dystonia have improved the understanding and treatment of this debilitating disorder.

Description

Dystonia as a term was first coined by Oppenheim in 1911 in reference to a childhood-onset syndrome he termed dystonia musculorum deformans. This entity, known as idiopathic torsion dystonia today, was noted to run in families, and although presumably inherited, was only recently proven to be of genetic cause. There is a wide range of variability in the manifestation of clinical symptoms of dystonia. Due to its various causes, dystonia is seen as a syndrome rather than a disease.

Dystonia can be classified by age of onset, cause, or by distribution of the body parts affected. Dystonia localized to a single body part such as the hand or neck is referred to as focal. Among body parts affected in focal dystonia, the eyelids, mouth, muscles controlling the voice, neck, hand, or arm may be affected. Dystonia localized to two contiguous body parts is referred to as segmental. Dystonia affecting body parts that are not next to each other is referred to as multifocal. Dystonia affecting one segment and another body part is classified as generalized. It may also affect only one half of the body and be called hemidystonia. Dystonia with a known environmental cause is referred to as secondary. The cause of primary or idiopathic dystonias is unknown or genetic.

The course and severity of dystonic symptoms may change over the duration of the illness. Symptoms may initially involve one body part and then spread to other body parts. The likelihood of spread often depends on the age and site of onset of symptoms. Early onset dystonia may start in a limb but tends to become generalized. Adult onset dystonia may start in the neck or face muscles and tends not to spread. Dystonia may first occur only with voluntary movements, but in time, occur at rest as well.

Demographics

Dystonia follows Parkinson's disease and essential tremor as the most frequent movement disorder. Prevalence is estimated as 3.4 per 100,000 for generalized forms and 29.5 per 100,000 for focal dystonia. Early onset dystonia may be more frequent in patients of Jewish ancestry, especially from Eastern Europe or Ashkenazi background.

Causes and symptoms

Causes

The exact cause of dystonia is unknown. Ongoing research on dystonia is directed at examining the abnormal brain activity in different parts of the brain such as the basal ganglia and cerebral cortex. The basal ganglia are a collection of nerve cells that are part of the brain pathways important for regulating aspects of normal movement. Abnormalities in the processing of information in these pathways are thought to underlie the various movement disorders such as Parkinson's disease, Huntington's disease, tremor, and dystonia. There is evidence for abnormalities in the spinal cord and peripheral nerves as well, suggesting that dystonia may involve abnormalities at multiple levels of the nervous system. Patients with dystonia may have abnormal touch perception and sensation, and theories propose that there may be defects in the preparation of movement as well as the translation of sensation to movement. Dystonia can be classified by cause into primary and secondary forms. Primary or idiopathic dystonia is presumed to be of genetic or unknown cause, whereas secondary dystonias are due to an attributable cause.

Primary dystonia

Primary or idiopathic dystonias have no identifiable etiology and are presumed to be genetic in cause. There are currently at least 13 different genetic dystonia syndromes, although only a few genes have actually been isolated. The only identified gene for primary dystonia is DYT1 on chromosome 9. DYT1 dystonia tends to occur in childhood and starts in a limb only to generalize. The appearance of the dystonia may differ in individuals with the same genetic abnormality, suggesting that there are environmental factors involved as well. Primary genetic dystonias may appear in multiple family members, but most are due to new mutations in genes and referred to as sporadic. Primary dystonias tend to develop gradually over the course of months to years.

Secondary dystonia

Secondary dystonia can be caused by a structural abnormality of the brain such as a stroke or infection, drugs or various toxins or metabolic abnormalities. These tend to occur over the course of days to weeks due to the nature of an inciting insult. Dystonia may occur after birth trauma and may be delayed in onset for up to a decade or later. Some may occur as part of a larger disease process affecting other parts of the body such as Wilson's disease, a defect of metabolism of copper that causes abnormal liver function and movement problems such as dystonia or tremor. Usually an abnormality will be found on brain imaging studies such as MRI or CT scan . Patients taking medications for psychiatric diseases such as schizophrenia or psychosis may develop dystonia as a drug reaction. Dystonia may be feigned as part of a psychiatric disorder and is then known as psychogenic.

Other dystonias

Dystonia may also be associated with other neurologic disorders. These are classified as dystonia-plus syndromes. Dystonia may be associated with Parkinson's disease or myoclonus , another movement disorder which consists of muscle jerking. Dystonia may be part of a larger syndrome of neurodegenerative disorders, a group of diseases which are caused by degeneration of nerve cells in certain portions of the brain. Such disorders include Huntington's disease and Parkinson's disease.

Symptoms

The symptoms of dystonia depend on the body part affected. Dystonia localized to the face may involve repetitive blinking, tongue protrusion, or jaw clenching. Blinking can become so severe that the patient can not see due to inability to open the eyes. Dystonia affecting the neck may lead to sustained flexion, extension, or twisting postures of the neck known as torticollis. Some dystonias are task-specific and only arise during the performance of certain tasks such as writing, typing, or playing instruments. The progression of these symptoms can lead to severe disability and inability to perform daily work. Generalized dystonia, the most severe form, can present as twisting movements of the head, trunk, and arms, completely disabling the affected individual. Dystonia can often be associated with a tremor in the affected body part. All forms of dystonia impair normal movement and daily function to some degree. Dystonia can be worsened by stress and anxiety, whereas it may be relieved with relaxation and sleep. Symptoms may be improved by touching various parts of the body in a phenomenon called a "sensory trick."

Diagnosis

The diagnosis of dystonia is clinical and is usually made by a neurologist who may have expertise with movement disorders. Investigation of dystonia will usually involve a physical examination and medical history taken by the neurologist to look for secondary causes such as drug exposure or stroke or other family members affected, suggesting a genetic cause. An MRI of the brain may be performed to look for a structural abnormality causing the symptoms. Laboratory testing may reveal abnormalities of copper metabolism associated with Wilson's disease. Genetic testing for the DYT1 gene is not performed unless the dystonia is early in onset or there is a family history of similar symptoms.

Treatment team

Treatment for dystonia involves the interaction between a neurologist, psychiatrists, and physical and occupational therapists. Treatment may involve a neurosurgeon for symptoms that do not respond to medical management. Dystonia of childhood onset is treated by a pediatric neurologist cooperating with pediatricians and pediatric therapists.

Treatment

Treatment for dystonia is usually directed towards management of the symptoms and depends on the type of dystonia. Dystonia that is associated or caused by known etiologies such as drugs, Wilson's disease, or dopa-responsive dystonia may be improved by treating the underlying disease with resolution of symptoms. The various treatments available may be grouped into oral medications, botulinum toxin injections, and surgical modalities.

Medications

Various oral medications are available for the symptomatic treatment of dystonia. Among these are various medications that affect different neurochemical systems thought to be important in causing dystonia. Some patients with symptoms of early onset may have dystonia that responds dramatically to levodopa. Anticholinergics , dopamine depleting agents, benzodiazepines , baclofen, or atypical antipsychotics may be tried as well.

Botox

Chemical denervation using botulinum toxin has been used for many movement disorders including dystonia. Botulinum toxin blocks the transmission of nerve impulses to the muscle and paralyzes the overactive muscles involved. Focal forms of dystonia are more amenable to treatment due to the ease of localizing injectable muscles and less extensive involvement. Botox may be used in generalized dystonia to facilitate improvement in select muscles needed for daily function such as the arms and legs.

Surgical treatment

Selective destruction or high frequency stimulation of nerve centers involved in causing dystonia has been useful in treating selected patients with disabling symptoms. Patients with generalized dystonia or hemidystonia may benefit due to the widespread nature of symptoms, limiting the efficacy of medications and botox injections. Surgical lesioning of nerve cells in the globus pallidus or stimulation of cells in the globus pallidus or subthalamic nucleus have been shown to be effective in treating the symptoms of dystonia. The long-term benefit of surgical therapies on symptoms of dystonia has yet to be validated.

Recovery and rehabilitation

Symptoms of dystonia may fluctuate over the course of years. The course of disease in any given individual can not be predicted. Some may improve spontaneously, whereas others may progress and spread to involve other body parts. Physical therapists may aid in the treatment of symptoms of dystonia. Treatment is focused on maintaining or improving the patient's ability to walk. Occupational therapy may be helpful in improving hand use.

Clinical trials

Several clinical trials are currently in effect for treatment of dystonia. The National Institutes of Health (NIH) and National Institutes of Neurological Diseases and Stroke (NINDS) are recruiting patients for trials examining the effect of different medications, botulinum toxin treatment, and surgical treatment for patients with dystonia. Studies are also ongoing to study the effect of electrical stimulation of the brain and nerves with magnetic fields to treat dystonia. Updated information on clinical trials can be found at the National Institutes of Health clinical trials website at www.clinicaltrials.org.

Prognosis

The prognosis for dystonia depends on the distribution and the cause. The initial site of symptoms may predict the prognosis. Patients with symptoms that start in the leg have a higher likelihood (90%) of progression to involve other body parts and become generalized. Patients with symptoms starting in the neck and later in onset have a much lower likelihood of spread. Most focal dystonias respond to medications or botulinum toxin. Refractory and generalized dystonia may require surgical management. Most patients have a normal life expectancy although with continued disabling symptoms.

Special concerns

Educational and social needs

Dystonia in many cases is a chronic illness and due to the physical limitations and often disfiguring symptoms, may lead to feelings of depression or anxiety. These feelings may require treatment by a psychiatrist if severe enough. It is important for patients with dystonia to continue to be involved in community activities and social events.

Resources

BOOKS

Bradley, Walter G., Robert Daroff, Gerald Fenichel, and C. David Marsden. Neurology in Clinical Practice. Newton, MA: Butterworth-Heinemann, 2000.

Rowland, Lewis, ed. Merritt's Textbook of Neurology. Philadelphia, PA: Lippincott Williams & Wilkins, 2000.

PERIODICALS

Klein, C., and L. J. Ozelius. "Dystonia: clinical features, genetics, and treatment." Current Opinion in Neurology 15 (2002): 491497.

Langlois, M., F. Richer, and S. Chouinard. "New Perspectives on Dystonia." Canadian Journal of Neurological Sciences 30, Suppl. 1 (2003): S34S44.

Volkmann, J., and R. Benecke. "Deep Brain Stimulation for Dystonia: Patient Selection and Evaluation." Movement Disorders 17 (2002): S112S115.

WEBSITES

NINDS Dystonias Information Page. National Institutes of Neurological Disorders and Stroke (NINDS). July 1, 2001. (June 7, 2004). <http://www.ninds.nih.gov/health_and_medical/disorders/the_dystonias.htm>

ORGANIZATIONS

Dystonia Medical Research Foundation. 1 East Wacker Drive, Suite 2430, Chicago, IL 60601-1905. (312) 755-0198; Fax: (312) 803-0138. dystonia@dystonia-foundation.org/ <http://www.dystonia-foundation.org>.

Worldwide Education & Awareness for Movement Disorders (WE MOVE). 204 West 84th Street, New York, NY 10024. (212) 875-8312 or (800) 437-6682; Fax: (212) 875-8389. wemove@wemove.org. <http://www.wemove.org>.

Peter T. Lin, MD

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dystonia

dystonia (dis-toh-niă) n. muscle dysfunction characterized by spasms or abnormal muscle contraction. Forms of dystonia include torticollis, blepharospasm, and writer's cramp. Another form is a postural disorder often associated with disease of the basal ganglia in the brain.
dystonic adj.

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