Ataxia refers to a patient's inability to coordinate their movements and to maintain balance. Since those skills are mainly controlled by the cerebellum, lesions of this part of the central nervous system may result in cerebellar ataxia.
As per definition, CA is a movement disorder associated with coordination and balance problems. These are most easily recognized while observing the patient's gait as well as their limb and eye movements. In detail, the following may be observed :
- Vertigo and dizziness
- Imbalance and unsteady, staggering gait as well as impaired tandem gait
- Hypotonia, tremor, dysdiadochokinesia, adysdiadochokinesia, grasping deficits and dysmetria, i.e., reduced muscle tones and involuntary contractions of muscles, the inability to rapidly perform alternating or targeted movements and to control motion ranges
- Instability of ocular alignment, saccadic intrusions and nystagmus, smooth pursuit impairment
- Abnormal vestibulo-ocular reflex
With regards to the patients life quality and if severe, these conditions may result in the inability to perform routine duties and may provoke frequent falls. In contrast, mild CA may only be noted while realizing determined tasks that require highly developed motor skills. Also, CA patients don't generally show all of the aforementioned symptoms.
The presence of additional symptoms may be helpful in identifying the cerebellum as the site of lesion: A patient presenting with ataxic dysarthria, for instance, is highly suspicious of cerebellar damage. Furthermore, cerebellar lesions often comprise cognitive and limbic regions and thus, corresponding non-motor neurological deficits may be observed, which in total have been referred to as Schmahmann's syndrome. They mainly consist in :
Entire Body System
walking Speech disturbances with slurred speech and changes in tone, pitch, and volume Visual complaints Abnormal eye movements Headache Nausea and vomiting Lightheadedness Changes in mental state, such as personality or behavioral changes Chaotic eye [cookchildrens.org]
This work describes for the first time the human phenotype associated with homozygous partial deletion of GRID2 in 3 children in one large consanguineous Turkish family. [ncbi.nlm.nih.gov]
The usual clinical features are constipation, fatigue, cold intolerance and weight gain. Rarely it can present with neurologic problems like reversible cerebellar ataxia, dementia, peripheral neuropathy, psychosis and coma. [ncbi.nlm.nih.gov]
We describe the molecular basis of a distinctive syndrome characterized by infantile stress-induced episodic weakness, ataxia, and sensorineural hearing loss, with permanent areflexia and optic nerve pallor. [ncbi.nlm.nih.gov]
Spinocerebellar ataxias (SCAs) are a heterogeneous group of autosomal dominant cerebellar ataxias clinically characterized by progressive ataxia, dysarthria and a range of other concomitant neurological symptoms. [ncbi.nlm.nih.gov]
Truncal ataxia Patients can't sit or stand unsupported and tend to fall backwards. It is caused by a midline cerebellar lesion, or may be a feature of post-chickenpox cerebellar syndrome. [patient.info]
ataxia, dysarthric speech and intention tremor), associated with cerebellar hypoplasia. [orpha.net]
For instance, damage to the midline cerebellar structures induces gait and truncal ataxia, while damage to the unilateral cerebellar hemisphere causes ipsilateral limb cerebellar ataxia. [frontiersin.org]
On examination at our hospital, he had noticeable cerebellar dysarthria, appendicular cerebellar signs, and pronounced truncal ataxia. Limb motor strength and sensation were normal. He had no diplopia and no nystagmus. [thelancet.com]
The most common presenting sign was ataxic gait; however, truncal ataxia, action tremor, and dysmetria were also frequently seen. [medlink.com]
aphasia Aboulia parietal lobe: Receptive aphasia Hemispatial neglect Gerstmann syndrome Astereognosis occipital lobe: Bálint's syndrome Cortical blindness Pure alexia temporal lobe: Cortical deafness Prosopagnosia Thalamus Thalamic syndrome Other Subclavian [en.wikipedia.org]
The second patient, known to have SLE, presented with crossed hemiplegia and cerebellar symptoms. Imaging studies showed cerebellar atrophy as well as thalamic and brainstem lesions. The patient had partial improvement with immunosuppression. [ncbi.nlm.nih.gov]
We describe a case of non-communicating hydrocephalus in a 36-year-old woman who presented a three-year history of cerebellar ataxia. [ncbi.nlm.nih.gov]
Diagnosis of CA and its underlying disease is based on thorough anamnesis, general and neurologic examination as well as neuroimaging. The former are particularly important since they may allow for a differentiation between spinal and cerebellar causes of ataxia, and because cerebellar lesions seen in images are often unspecific. For instance, it may not be possible to associate those findings to a determined entity without knowing if symptoms worsen progressively, or if the disease is characterized by episodes of remission and recurrence. Age is another key factor.
Virtually all patients with suspected CA should undergo magnetic resonance imaging (MRI) of the brain. Exceptions may be made for patients with a family history of a corresponding genetic disorder. With regards to MRI, the most common finding is cerebellar atrophy. Neuroimaging may also reveal the presence of a neoplasm or an abscess.
Depending on the results obtained so far, additional diagnostic measures may be necessary to determine the underlying disorder. If gene defects are suspected, samples for genetic screens have to be obtained.
Regeneration capacities of the central nervous systems are very limited. Accordingly, neurological deficits provoked by cerebellar lesions are often irreversible, and it is of great importance to initiate treatment as early as possible in order to avoid an aggravation of symptoms. Specific treatment options largely depend on the underlying disease and may range from dietary adjustments to drug therapy to surgical intervention. In any case, patients suffering from CA should participate in rehabilitation programs. Patients are to perform balance and coordination exercises to regain their ability to walk independently, to dominate their posture and to use their limbs in a controlled manner . Frenkel exercises are often recommended to this end. Nevertheless, some patients may not be able to return to their everyday lives without using orthopedic aids .
With regards to symptomatic therapy of CA, modulators of serotonergic signaling may be applied. In particular, buspirone, an agonist of serotonin receptor 1A, is used to treat mild to moderate CA . However, some patients may not respond to such treatment and this also applies to the use of serotonin reuptake inhibitors and antagonists of serotonin receptor 3  . Additionally, few studies suggest that administration of amantadine, memantine and riluzole may have beneficial effects .
More recent approaches to CA therapy involve transcranial direct current stimulation and magnetic stimulation of the cerebellum  . Both aim at modulating the excitability of cerebellar neurons.
The life expectancy of CA patients is unaltered, unless cerebellar lesions are caused by diseases associated with a poor prognosis for life. Such may be the case in patients suffering from brain tumors. However, for many forms of CA, treatment options are very limited. Neuronal damage is frequently irreversible, but it may be possible to halt disease progression. Few diseases are associated with a very good prognosis. Acute cerebellar ataxia, for instance, is usually self-limiting and patients can expect to recover fully within few weeks .
Congenital forms of CA are to be distinguished from acquired forms of the disease. With respect to the former, several genetic disorders have been related to cerebellar malfunction and consequent ataxia. Such diseases may be inherited with an autosomal recessive (ARCA), autsomal dominant (ADCA), X-linked or mitochondrial trait. Both ARCA and ADCA are heterogenous groups of neurodegenerative diseases, but the latter designations also comprise several entities. Some of those diseases pertaining to these four groups are listed below; the interested reader is referred to more extensive reviews available elsewhere   .
- Cerebellar hypoplasia due to mutations of the OPHN1 or CASK gene
- Fragile X-associated tremor/ataxia syndrome
- Mitochondrial inheritance 
- Kearns-Sayre syndrome
- MELAS syndrome
- Myoclonic epilepsy with ragged red fibers (MERRF)
To some extent, these diseases differ regarding their manifestation. For instance, loss of proprioception and pallesthesia as well as blunted reflexes are most commonly observed in ARCA.
Besides hereditary forms of CA, there are numerous other factors that may inflict cerebellar damage and thus provoke CA.
- Autoimmune disease
- Cerebellar stroke syndrome
- Demyelinating disease like multiple sclerosis
- Infection (e.g., acute cerebellar ataxia manifests few weeks after viral infection and infectious mononucleosis, influenza, measles or mumps)
- Intoxication with alcohol, illicit drugs or statins
- Nutritional deficiency (e.g., vitamins B12 and E, folate and copper)
Of note, other classification systems than the one presented here exist. Forms of CA may also be assigned to distinct groups on the basis of the underlying pathophysiological mechanisms (e.g., metabolic and degenerative disorders), further involved anatomical structures (e.g., pure cerebellar and spinocerebellar diseases), the course of the disease (e.g., intermittent, persistent, chronic and progressive) as well as the mean age at symptom onset (early-onset vs. late-onset).
Incidence and prevalence rates as well as gender, racial and age distribution patterns vary with different forms of CA. With regards to inherited CA, the most frequent disorder is Friedreich ataxia, which affects 1 in 30,000 to 50,000 people. CA due to multiple sclerosis, stroke, trauma or tumor are rather common forms of acquired CA. In sum, CA prevalence may amount to approximately 8 per 100,000 inhabitants, with 5 and 3 people suffering from hereditary and non-hereditary diseases, respectively .
While onset of symptoms related to genetic diseases typically occurs in infancy or childhood, the aforementioned forms of acquired CA is usually diagnosed in adults and the elderly. Children presenting with acquired ataxia most commonly suffer from acute cerebellar ataxia. It has been reported that the median age of CA symptom onset is in the fourth decade of life, but due to the aforementioned heterogeneity of disorders associated with CA, this statistical specification is of little relevance to clinical practice.
Cerebellum and pons are the main parts of the metencephalon and this part of the brain is located in the posterior cranial fossa. The cerebellum plays a pivotal role in motor control and maintenance of balance and posture. From an anatomical point of view, it consists of three main portions, the anterior lobe, the posterior lobe and the flocculonodular lobe. These correspond only partially to the cerebellum's functional sections, which have been designated vestibulocerebellum, spinocerebellum and pontocerebellum: The vestibular system is connected to the vestibulocerebellum by sensory afferent nerves, and based on the input received, balance, posture and eye movements are coordinated. This function is complemented by the spinocerebellum, whose task is to process afferent stimuli originating from the spinal cord and muscle spindles, i.e., to control the position of limbs, trunk and head, and to adjust the muscle tone if necessary. Many complex movements require participation of the cerebral cortex and a connection between both structures is established by the pontocerebellum. Consequently, the single most characteristic symptom of cerebellar lesions is CA.
The molecular basis of CA varies widely. Since ion channels are of major importance for neuronal function, it is little surprising that several forms of CA are indeed channelopathies. Corresponding gene defects are often inherited with an autosomal dominant trait and affect calcium and potassium channels . Such has been proven for ADCA episodic ataxia and spinocerebellar ataxia, but the pathomechanisms causing vestibulocerebellar syndrome are only poorly understood.
For most forms of CA, no specific measures can be recommended. Since acute cerebellar ataxia is associated with viral infectious diseases, compliance with vaccination plans may reduce the individual risk of this disorder, though.
In general, the term ataxia describes a movement disorder characterized by a limited ability to maintain balance and posture, and/or to move limbs and eyes in a coordinated way. This description already implies that the clinical presentation of ataxic patients varies largely, and this may partially be explained by the fact that distinct parts of the central nervous system as well as subordinated structures are involved in planning and execution of a targeted movement. In detail, lesions of sensory pathways, spinal cord, basal ganglia, cerebellum and cerebral cortex may cause ataxia . If cerebellar function is impaired and provokes such movement disorders, the patient is diagnosed with cerebellar ataxia (CA).
As is the case with lesions of any of the aforementioned structures, neurological deficits are rarely limited to ataxia in patients who sustained cerebellar damage. Besides CA, motor and coordination deficits of speech are observed frequently. Also, cognitive and affective functions may be impaired. Only the entirety of anamnestic data, neurological findings and data obtained by means of neuroimaging allow for associating an individual case with one of several differential diagnoses. As it is, CA may be related to genetic disorders, to inflammatory or immune-mediated pathophysiological processes, to neoplasms, trauma, vascular accidents or nutrient deficiencies.
In general, the term ataxia describes the patient's reduced ability to coordinate their movements, to maintain posture and balance. Complex neural circuits are involved in those processes and accordingly, ataxia may be triggered by a wide variety of lesions. In detail, functional impairment of sensory pathways, spinal cord, basal ganglia, cerebellum and cerebral cortex may cause ataxia. If ataxia occurs to pathophysiological events interfering with cerebellar function, the respective patient is diagnosed with cerebellar ataxia (CA).
CA may be provoked by genetic disorders, by autoimmune diseases, strokes, traumas and tumors, among others. CA typically manifests in form of vertigo and dizziness, an unsteady gait and problems upon controlling the movements of limbs and eyes. Moreover, cerebellar lesions are often associated with difficulties while speaking, writing and reading. All these symptoms are rather unspecific and in order to obtain more detailed information regarding the underlying disease, patients usually have to undergo magnetic resonance imaging and possibly additional procedures.
Only if a reliable diagnosis can be made, the appropriate therapeutic approach can be chosen. Causal treatment is available for few diseases associated with CA only, and symptomatic support may be provided in form of medication or surgery. Some patients, e.g., children suffering from post-infectious CA, have a very good prognosis, while others, namely those diagnosed with brain tumors, have a poor one.
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