Dystonia

# Overview
Dystonia is a hyperkinetic movement disorder identified by involuntary sustained or intermittent contraction of a single or group of muscles that leads to repetitive movements or abnormal posture. The typical dystonic movements are usually rhythmic or patterned contractions that may be accompanied by tremor.

# Historical Perspective
- The term Dystonia was first introduced by Hermann Oppenheim, a German Neurologist , in 1911 following delineating abnormal posturing (dystonia muscularum deformans) in 4 unrelated Jewish children.
- The association between hereditary factors and dystonia was made in 1959 during reporting families with similar symptoms . 
- The association between genes and dystonia was made in 1989 during introducing DYT1 or TOR1A gene as a major cause of young-onset generalized dystonia .
- In 1989, Ozelius .et.al were the first to discover the association between ITD1 gene ( further known as DYT1 gene ) and the development of dystonia. 
- The variant "Focal Dystonia" was first introduced by Charles David Marsden, an English Neurologist, in 1976, following reporting different cases of adult-onset blepharospasm and/or oromandibular dystonia,, torticollis, spasmodic dysphonia, and writers  cramp without any hereditary background or known cause. 

# Classification
Dystonia may be classified into several subtypes based on age of onset, topographic distribution, temporal aspects, associated clinical features and etiology .
- Dystonia may be classified into five subtypes based on the age of onset; infancy (up to two years), childhood (3-12 years), adolescence (13-20 years), early adulthood (21-40 years) and late adulthood (>40 years)
- Dystonia  may be classified into five subtypes based on the topographic distribution : focal, segmental, multifocal, generalized or hemidystonia
-  Focal : if only one body part of the body is involved. The examples include writing dystonia, cervical dystonia, blepharospasm, Oromandibular dystonia and laryngeal or lingual dystonia
-  Segmental : if two or more contiguous parts are involved. The examples include bi-brachial and cranial dystonia.
-  Multifocal : if two or more noncontiguous parts are involved. The examples include dystonia of the right arm and the left leg
-  Hemidystonia : if half of the body is involved.
- Dystonia is classified as generalized if trunk and two or more other parts are involved.
- Dystonia may be classified into eight subtypes based on the temporal aspects of the disease : manner of onset (acute versus insidious), symptoms variability (diurnal, intermittent, or action induced), and overall progression (static versus progressive).
- Dystonia may be classified into five subtypes based on associated clinical features:
- Dystonia is classified into four subtypes based on the etiology: Known Pathology of the nervous system, inherited, acquired or idiopathic
-  Nervous system pathology : if there are any structural lesion or confirmed degeneration
-  Inherited: if there is autosomal dominant, autosomal recessive ,  X-linked recessive or mitochondrial pattern of inheritance
- Acquired : if there is any history of brain injury, infection, toxic or drug consumption, vascular event, neoplasm or psychogenic cause
- Idiopathic

# Pathophysiology
Th exact pathogenesis of dystonia is not fully understood. However, the main mechanism has been attributed to the impaired central inhibitory circuits. It is thought that dystonia is the result of changes in synaptic pathways, reduced brain inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and decreased inhibition at the level of spinal, brain stem and especially cortex of the brain.  It is also thought that dystonia may be associated with microscopic changes in brain stem nuclei, loss of Purkinje cells and axonal swelling in the cerebellum, changes in basal ganglia-cerebello-thalamo-cortical pathway and cerebellar and basal ganglia structures.

# Causes
Common known causes of dystonia include:
- Genetic mutations in TOR1A, THAP1, GCH1 and KMT2B
- Brain injury or infections including perinatal hopoxic injury, encephalitis, brain abscess or neoplasms, stroke and neurotoxic agents that affect basal ganglia (especially putamen), cerebellum, thalamus regions
- Diseases contributing to degenerative changes in central nervous system including Wilson's disease, GM1 and GM2 gangliosidosis, homocyctinuria, Lesch Nyhan syndrome and ataxia-telangiectasia
- Drugs including dopamin receptor blocking agents, amine depletors, serotonin-reuptake inhibitors, monoamine-oxidase inhibitors, calcium antagonists, benzodiazepines, general anesthetic agents, carbamazepine, phenytoin, triptans, ranitidine, cocaine or ecstasy

# Differential diagnosis
Dystonia must be differentiated from other diseases that cause neurological manifestations in infants.

# Treatment
Treatment has been limited to minimizing the symptoms of the disorder as there is yet no successful treatment for its cause. Reducing the types of movements that trigger or worsen dystonic symptoms provides some relief as does reducing stress, getting plenty of rest, moderate exercise and relaxation techniques. Various treatments focus on sedating brain functions or blocking nerve communications with the muscles via drugs, neuro-suppression or denervation. All current treatments have negative side affects and risks.
Physicians may prescribe a series of different medications on a trial-and-error basis in an effort to find a combination that is effective for a specific patient. Not all patients will respond well to the same medications. Drugs that have had positive results in some patients include anti-Parkinsons agents (Trihexyphenidyl), muscle relaxers (Valium), keppra, and beta-blockers including "off-label" uses for some blood pressure medications.
Drugs, such as anticholinergics which act as an inhibitor of the neurotransmitter acetylcholine, may provide some relief. Clonazepam, an anti-seizure medicine, is also sometimes prescribed. However, for most sufferers their effects are limited and side affects like mental confusion, sedation, mood swings and short term memory loss occur.
Botulinum toxin injections into affected muscles have proved quite successful in providing some relief for around 3-6 months, depending on the kind of dystonia. Bo-Tox injections have the advantage of ready avalibility (the same form is used for cosmetic surgery) and the affects are not permanent. There is a risk of temporary paralysis of the muscles being injected or the leaking of the toxin into adjacent muscle groups causing weakness or paralysis in them. The injections have to be repeated as the effects wear off and around 15% of recipients will develop immunity to the toxin. There is a Type A and Type B toxin approved for treatment of dystonia; often those that develop resistance to Type A may be able to use Type B.
Surgery, such as the denervation of selected muscles, may also provide some relief, however, the destruction of nerves in the limbs or brain is not reversable and should only be considered in the most extreme cases. Recently, the procedure of deep brain stimulation (DBS) has proved successful in a number of cases of severe generalised dystonia.
One type of dystonia, dopa-responsive dystonia can be completely treated with regular doses of L-dopa in a form such as Sinemet (carbidopa/levodopa). Although this doesn't remove the condition, it does alleviate the symptoms most of the time.
A baclofen pump has been used to treat patients of all ages exhibiting muscle spasticity along with dystonia.  The pump delivers baclofen via a catheter to the thecal space surrounding the spinal chord.  The pump itself is placed in the abdomen.  It can be refilled periodically by access through the skin.
Physical therapy can sometimes help with focal dystonia.  A structured set of exercises are tailored to help the affected area.