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definition : ataxia

Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that includes gait abnormality. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum. Ataxia can be limited to one side of the body, which is referred to as hemiataxia. Several possible causes exist for these patterns of neurological dysfunction. Dystaxia is a mild degree of ataxia. Friedreich's ataxia has gait abnormality as the most commonly presented symptom. The word is from Greek α- [a negative prefix] + -τάξις [order] = "lack of order".

== Types ==

=== Cerebellar ===

The term cerebellar ataxia is used to indicate ataxia that is due to dysfunction of the cerebellum. The cerebellum is responsible for integrating a significant amount of neural information that is used to coordinate smoothly ongoing movements and to participate in motor planning. Although ataxia is not present with all cerebellar lesions, many conditions affecting the cerebellum do produce ataxia. People with cerebellar ataxia may have trouble regulating the force, range, direction, velocity and rhythm of muscle contractions. This results in a characteristic type of irregular, uncoordinated movement that can manifest itself in many possible ways, such as asthenia, asynergy, delayed reaction time, and dyschronometria. Individuals with cerebellar ataxia could also display instability of gait, difficulty with eye movements, dysarthria, dysphagia, hypotonia, dysmetria and dysdiadochokinesia. Interaction torques are created at an associated joint when the primary joint is moved. For example, if a movement required reaching to touch a target in front of the body, flexion at the shoulder would create a torque at the elbow, while extension of the elbow would create a torque at the wrist. These torques increase as the speed of movement increases and must be compensated and adjusted for to create coordinated movement. This may, therefore, explain decreased coordination at higher movement velocities and accelerations.

* Dysfunction of the vestibulocerebellum (flocculonodular lobe) impairs the balance and the control of eye movements. This presents itself with postural instability, in which the person tends to separate his/her feet upon standing, to gain a wider base and to avoid titubation (bodily oscillations tending to be forward-backward ones). The instability is therefore worsened when standing with the feet together, regardless of whether the eyes are open or closed. This is a negative Romberg's test, or more accurately, it denotes the individual's inability to carry out the test, because the individual feels unstable even with open eyes. * Dysfunction of the spinocerebellum (vermis and associated areas near the midline) presents itself with a wide-based "drunken sailor" gait (called truncal ataxia), characterised by uncertain starts and stops, lateral deviations, and unequal steps. As a result of this gait impairment, falling is a concern in patients with ataxia. Studies examining falls in this population show that 74-93% of patients have fallen at least once in the past year and up to 60% admit to fear of falling. * Dysfunction of the cerebrocerebellum (lateral hemispheres) presents as disturbances in carrying out voluntary, planned movements by the extremities (called appendicular ataxia). **inability to judge distances or ranges of movement. This is known as dysmetria and is often seen as undershooting, hypometria, or overshooting, hypermetria, the required distance or range to reach a target. This is sometimes seen when a patient is asked to reach out and touch someone's finger or touch his or her own nose. and various other recreational drugs (e.g. ketamine, PCP or dextromethorphan, all of which are NMDA receptor antagonists that produce a dissociative state at high doses). A further class of pharmaceuticals which can cause short term ataxia, especially in high doses are the benzodiazepines. Exposure to high levels of methylmercury, through consumption of fish with high mercury concentrations, is also a known cause of ataxia and other neurological disorders.

=== Radiation poisoning ===

Ataxia can be induced as a result of severe acute radiation poisoning with an absorbed dose of more than 30 Grays.

=== Vitamin B12 deficiency ===

Vitamin B12 deficiency may cause, among several neurological abnormalities, overlapping cerebellar and sensory ataxia.

=== Hypothyroidism ===

Symptoms of neurological dysfunction may be the presenting feature in some patients with hypothyroidism. These include reversible cerebellar ataxia, dementia, peripheral neuropathy, psychosis and coma. Most of the neurological complications improve completely after thyroid hormone replacement therapy.

=== Causes of isolated sensory ataxia ===

Peripheral neuropathies may cause generalised or localised sensory ataxia (e.g. a limb only) depending on the extent of the neuropathic involvement. Spinal disorders of various types may cause sensory ataxia from the lesioned level below, when they involve the dorsal columns

=== Non-hereditary cerebellar degeneration === Non-hereditary causes of cerebellar degeneration include chronic ethanol abuse, head injury, paraneoplastic and non-paraneoplastic autoimmune ataxia, high altitude cerebral oedema, coeliac disease, normal pressure hydrocephalus and infectious or post-infectious cerebellitis.

=== Hereditary ataxias ===

Ataxia may depend on hereditary disorders consisting of degeneration of the cerebellum and/or of the spine; most cases feature both to some extent, and therefore present with overlapping cerebellar and sensory ataxia, even though one is often more evident than the other. Hereditary disorders causing ataxia include autosomal dominant ones such as spinocerebellar ataxia, episodic ataxia, and dentatorubropallidoluysian atrophy, as well as autosomal recessive disorders such as Friedreich's ataxia (sensory and cerebellar, with the former predominating) and Niemann Pick disease, ataxia-telangiectasia (sensory and cerebellar, with the latter predominating), and abetalipoproteinaemia. An example of X-linked ataxic condition is the rare fragile X-associated tremor/ataxia syndrome.

=== Arnold-Chiari malformation (congenital ataxia) ===

Arnold-Chiari malformation is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils and the medulla through the foramen magnum, sometimes causing hydrocephalus as a result of obstruction of cerebrospinal fluid outflow.

=== Succinic Semialdehyde Dehydrogenase Deficiency ===

Succinic semialdehyde dehydrogenase deficiency is an autosomal-recessive gene disorder where mutations in the ALDH5A1 gene results in the accumulation of gamma-Hydroxybutyric acid (GHB) in the body. GHB accumulates in the nervous system and can cause ataxia as well as other neurological dysfunction.

=== Wilson's disease ===

Wilson's disease is an autosomal-recessive gene disorder whereby an alteration of the ATP7B gene results in an inability to properly excrete copper from the body. Copper accumulates in the nervous system and liver and can cause ataxia as well as other neurological and organ impairments.

=== Gluten ataxia ===

Gluten ataxia is a gluten-related disorder, a wide spectrum of disorders marked by an abnormal immunological response to gluten. Like celiac disease, it is an autoimmune disease. With gluten ataxia, damage takes place in the cerebellum, the balance center of the brain that controls coordination and complex movements like walking, speaking and swallowing. Gluten ataxia is the single most common cause of sporadic idiopathic ataxia.

Gluten ataxia is an immune-mediated disease triggered by the ingestion of gluten in genetically susceptible individuals. It should be considered in the differential diagnosis of all patients with idiopathic sporadic ataxia. Early diagnosis and treatment with a gluten free diet can improve ataxia and prevent its progression. Readily available and sensitive markers of gluten ataxia include anti-gliadin antibodies. Immunoglobulin A (IgA) deposits against transglutaminase 2 (TG2) in the small bowel and at extraintestinal sites are proving to be additionally reliable and perhaps more specific markers of the whole spectrum of gluten sensitivity. They may also hold the key to its pathogenesis.

Gluten ataxia is defined as sporadic cerebellar ataxia associated with the presence circulating antigliadin antibodies and in the absence of an alternative cause for ataxia.

=== Sodium-potassium pump ===

Malfunction of the sodium-potassium pump may be a factor in some ataxias. The - pump has been shown to control and set the intrinsic activity mode of cerebellar Purkinje neurons. This suggests that the pump might not simply be a homeostatic, "housekeeping" molecule for ionic gradients; but could be a computational element in the cerebellum and the brain. Indeed, an ouabain block of - pumps in the cerebellum of a live mouse results in it displaying ataxia and dystonia. Ataxia is observed for lower ouabain concentrations, dystonia is observed at higher ouabain concentrations.


== Treatment ==

The treatment of ataxia and its effectiveness depend on the underlying cause. Treatment may limit or reduce the effects of ataxia, but it is unlikely to eliminate them entirely. Recovery tends to be better in individuals with a single focal injury (such as stroke or a benign tumour), compared to those who have a neurological degenerative condition. A review of the management of degenerative ataxia was published in 2009. A small number of rare conditions presenting with prominent cerebellar ataxia are amenable to specific treatment and recognition of these disorders is critical. Diseases include vitamin E deficiency, abetalipoproteinemia, cerebrotendinous xanthomatosis, Niemann–Pick type C disease, Refsum's disease, glucose transporter type 1 deficiency, episodic ataxia type 2, gluten ataxia, glutamic acid decarboxylase ataxia.

The movement disorders associated with ataxia can be managed by pharmacological treatments and through physical therapy and occupational therapy to reduce disability. Some drug treatments that have been used to control ataxia include: 5-hydroxytryptophan (5-HTP), idebenone, amantadine, physostigmine, L-carnitine or derivatives, trimethoprim/sulfamethoxazole, vigabatrin, phosphatidylcholine, acetazolamide, 4-aminopyridine, buspirone, and a combination of coenzyme Q10 and vitamin E. A recent systematic review suggested that physical therapy is effective, but there is only moderate evidence to support this conclusion. The most commonly used physical therapy interventions for cerebellar ataxia are vestibular habituation, Frenkel exercises, proprioceptive neuromuscular facilitation (PNF), and balance training; however, therapy is often highly individualized and gait and coordination training are large components of therapy.

Current research suggests that, if a person is able to walk with or without a mobility aid, physical therapy should include an exercise program addressing five components: static balance, dynamic balance, trunk-limb coordination, stairs, and contracture prevention. Once the physical therapist determines that the individual is able to safely perform parts of the program independently, it is important that the individual be prescribed and regularly engage in a supplementary home exercise program that incorporates these components to further improve long term outcomes. These outcomes include balance tasks, gait, and individual activities of daily living. While the improvements are attributed primarily to changes in the brain and not just the hip and/or ankle joints, it is still unknown whether the improvements are due to adaptations in the cerebellum or compensation by other areas of the brain. Training likely needs to be intense and focused—as indicated by one study performed with stroke patients experiencing limb ataxia who underwent intensive upper limb retraining. Their therapy consisted of constraint-induced movement therapy which resulted in improvements of their arm function. Other tools that assess motor function, balance and coordination are also highly valuable to help the therapist track the progress of their patient, as well as to quantify the patient's functionality. These tests include, but are not limited to: * The Berg Balance Scale * Tandem Walking (to test for Tandem gaitability) * Scale for the Assessment and Rating of Ataxia * tapping tests – The person must quickly and repeatedly tap their arm or leg while the therapist monitors the amount of dysdiadochokinesia. * finger-nose testing

== Other uses ==

The term "ataxia" is sometimes used in a broader sense to indicate lack of coordination in some physiological process. Examples include optic ataxia (lack of coordination between visual inputs and hand movements, resulting in inability to reach and grab objects) and ataxic respiration (lack of coordination in respiratory movements, usually due to dysfunction of the respiratory centres in the medulla oblongata). Optic ataxia may be caused by lesions to the posterior parietal cortex, which is responsible for combining and expressing positional information and relating it to movement. Outputs of the posterior parietal cortex include the spinal cord, brain stem motor pathways, pre-motor and pre-frontal cortex, basal ganglia and the cerebellum. Some neurons in the posterior parietal cortex are modulated by intention. Optic ataxia is usually part of Balint's syndrome, but can be seen in isolation with injuries to the superior parietal lobule, as it represents a disconnection between visual-association cortex and the frontal premotor and motor cortex.

== See also == *Ataxic cerebral palsy *Spinocerebellar ataxia *Bruns apraxia

== References ==

== Further reading == * *

== External links == * [ Friedreich's Ataxia Research Alliance (FARA)] * [ Ataxia Connect Social Network] * [ Ataxia UK], including [ guidelines] * [ Brasil, Rio Grande do Sul - Associação dos Amigos, Parentes e Portadores de Ataxias Dominantes] * [ Canadian Association for Familial Ataxias - Claude St-Jean Foundation] * [ International Ataxia Awareness Day] * [ LivingWithAtaxia Forums & Community] * [ Overview] at National Institute of Neurological Disorders and Stroke (NINDS) * [ Rochester Ataxia Foundation, Rochester, NY] * [ The latest news and research on Ataxia] * [ US National Ataxia Foundation] * [ University of Minnesota Ataxia Center] * [ Video demonstration of ataxic gait] * [ Gluten Ataxia] * [ Range of Neurologic Disorders in Patients With Celiac Disease] * [ The Cerebellum] * [ Cerebellum and Ataxias]

Category:Symptoms and signs: Nervous system Category:Cerebral palsy types Category:Stroke

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