Ataxia describes a lack of coordination while performing voluntary movements. It may appear as clumsiness, inaccuracy, or instability. Movements are not smooth, and may appear disjointed or jerky. Ataxia may affect any part of the body.

When it affects the arms and hands, it may cause tremor due to over-correction of inaccurate movements, past-pointing when an attempted reach overshoots the target, and poor performance of regular, repeated movements, such as hand clapping.

When ataxia affects mechanisms of walking, there will be instability with a tendency to fall. As a result, the child usually adopts a wide-based gait, with the feet spread further apart than the hips. This is done in an attempt to compensate for the instability. The gait may appear "drunken."

Balance may also be affected; the affected child may fall spontaneously or be unable to compensate for variations in the ground or a mild push from the side. When ataxia affects speech, it leads to "scanning" speech. In this form of speech, the voice is relatively monotone, often with a breathy sound accompanied by unusual accelerations or pauses between syllables.

When ataxia affects the eyes, rapid shifts of gaze to look at a particular object often miss. On careful examination, the eyes may be observed to overshoot or undershoot their mark, with "catch-up" movements.

Examination

The first feature to observe about ataxia is where it occurs in the child's body. It may affect only walking or arm and eye movements may be involved. Physicians may then determine its severity in each part of the body. It is important to recognize if...

The diagnosing physician may also be concerned about the progression of symptoms over time. Certain questions may be asked, including:

• Are the symptoms stable or have they become worse over the preceding weeks, months, or years?
• Did the symptoms begin after an illness?
• Have there been prior episodes of symptoms that have resolved?
• If the symptoms resolve and recur, how long do they last and do they become completely better?

Many types of ataxia are hereditary, so it is also important to look for subtle symptoms in family members. For example, the physician may question if there are relatives with clumsiness, frequent falling, late walking, early speech therapy, unusual eye movements, particularly poor handwriting, or other neurological problems.

Mechanism

Ataxia is usually caused by damage to the cerebellum or to its inputs or outputs. The cerebellum is a large structure at the lower back of the brain, just above and behind where the spinal cord enters the skull at the bottom. The cerebellum exists in essentially all vertebrate animals.

Separate parts of the cerebellum are concerned with control of arm movements, eye movements, trunk stability, balance, and gait. There are many theories describing the function and purpose of the cerebellum, but these issues have not yet been resolved. In general, many researchers believe that the cerebellum receives sensory information from the entire body, as well as a copy of the motor commands being sent to move the body. It integrates this information using a densely interconnected network of nerves in order to determine the interactions between sensations coming from different parts of the body and the expected results of movement. The resulting information is then sent to motor areas of the brain. This is done to presumably adjust the motor commands in order to compensate for the location of the limbs in space and the interaction of the forces generated by different parts of the body. The cerebellum appears to have a set of signals that tell it when movement errors occur, and these errors are used to make rapid corrections and thereby learn to improve performance.

Damage to the Cerebellum
When the cerebellum is damaged, the effects may often be understood by determining the regions that sustained the injury. A "focal" injury or an injury to a small local part of the cerebellum may affect only arm movements, balance, gait, or eye movements. This type of injury may be seen if there is a stroke, migraine, or tumor.

A more "global" injury may result in loss of a particular cell type. The Purkinje cells are large and complex cells that perform much of the integration in the cerebellum. These cells seem to be particularly susceptible to injury.

Certain poisons, medicines, and genetic diseases may lead to injury or loss of the Purkinje cells, causing causes symptoms that may simultaneously affect many functions of the cerebellum. In some cases, a child's cerebellum may not have formed properly in the first place.

Often the symptoms are relatively mild, as other brain areas may have taken over some lost functions (since parts of the cerebellum may have been absent during development of the rest of the brain).

Etiology

There are many diseases that may lead to ataxia. Determining which disease is the cause for a particular child's ataxia may be very difficult, and requires a careful series of steps planned by an experienced physician. Often, the diagnosis cannot be made immediately, but must await careful examination of the progression or resolution of symptoms over time. In some cases, however, it is important to make the diagnosis rapidly so that treatment may be started before further damage occurs.

Static (fixed) injury:
Cerebral palsy, stroke, trauma, hypoxic injury.

Neoplastic/Paraneoplastic:
Tumors of the cerebellum or brainstem, neuroblastoma in the chest or abdomen (associated with the myoclonus-opsoclonus-ataxia syndrome).

Degenerative/Demyelinating:
Ataxia-telangiectasia, ataxia oculomotor apraxia, Friedreich's ataxia, Wilson's disease, spinocerebellar ataxia (including Machado-Joseph disease), dentato-rubro-pallido-luysian atrophy (DRPLA), olivopontocerebellar atrophy (OPCA), Marinesco-Sjögren syndrome, multiple sclerosis, Pelizaeus-Merzbacher disease, Angelman syndrome

Chemical/metabolic:
Hartnup's disease, lipidoses, mitochondrial disorders (e.g., Leigh's disease, MERRF,  and pyruvate dehydrogenase complex deficiency, etc.), glutaric aciduria, Refsum's disease, vitamin deficiency (e.g., B12, E, thiamine, etc.), abetalipoproteinemia (Bassen-Kornzweig disease), lysosomal diseases (e.g., Krabbe's disease, meta-chromatic leukodystrophy, carnitine acetyltransferase deficiencies, juvenile Gaucher's disease, Tay-Sachs disease, etc.), ceroid lipofuscinosis, carbohydrate-deficient glycoprotein syndromes, biotinidase deficiency, holocarboxylase deficiency, Niemann-Pick type C

Malformations:
Joubert syndrome, Dandy-Walker malfor-mation, basilar impression, vermian agenesis, cerebellar dysgenesis, rhom-bencephalosynapsis, Chiari malformation (types 2 and 3), pontocerebellar hypoplasia

Drug-induced:
Anti-epileptic medications (particularly phenytoin and carbamazepine), anti-histamines, barbiturates, lithium, alcohol, chemotherapy, heavy metal poisoning (e.g., lead, mercury, thallium, etc.), bromide intoxication

Acute/Paroxysmal:
Acute cerebellar ataxia (acute symptoms are usually due to a virus or frequently following varicella infection).

Dominant familial episodic ataxias (type 1 lasts 10 to100 minutesassociated with myokymia and chorea, and treated with acetazolamide or phenytoin; type 2 lasts for 1 to 24 hours, starts during adolescence, may worsen during the child's lifetime, and is treated with acetazolamide or flunarizine), calcium "channelopathies," metabolic disease (e.g., propionic acidemia, maple-syrup urine disease and its thiamine-responsive variant, urea cycle disorders, etc.), porphyria, electrolyte or glucose abnormalities, Miller-Fisher variant of Guillain-Barré syndrome, basilar migraine

Disorders that mimic ataxia:
Weakness, hypothyroidism, low blood pressure, any peripheral neuropathy (with lack of sensation in the feet), astasia-abasia (usually psychogenic), seizures ("pseudo-ataxia"), paroxysmal vertigo (associated with migraines), myoclonus.

Workup

After listening to the history of the symptoms and examining the child, several steps that may be taken, depending on the particular circumstances.

The first question is whether the child has ataxia, or some condition that looks like ataxia. These conditions include weakness, a sensory nerve problem, low blood pressure, dizziness, or other types of movement disorder. 

If it appears that the child has ataxia, further studies often include laboratory tests and imaging studies. The most common initial laboratory tests include...