Focus on pediatric movement disorders: ataxia. (ask the doctor).

Most people take for granted their ability to control their body movement. We will ourselves to move--walk across a room---sit in a chair--or simply sit still. For millions of children, however, these simple, everyday acts are frustratingly difficult, if not impossible. These children are living with neurologic movement disorders.

The major neurologic movement disorders that may affect children include ataxia, bradykinesia, choreoathetosis, dystonia, myoclonus, spasticity, tics, and tremor. In this article, the first of several pieces about pediatric movement disorders, the causes, clinical evaluation, diagnosis, and treatment of ataxia are discussed.

WHAT IS ATAXIA?

Ataxia is a condition related to movement and is characterized by 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 walking, there is instability with a tendency to fall. As a result, affected children usually adopt a wide-based gait, with the feet spread further apart than the hips. This is done in an attempt to compensate for the instability.

Balance may also be affected. Children with ataxia 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 in nature and often has 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 their mark. Upon careful examination, the eyes may be observed to overshoot or undershoot their mark, with "catch-up" movements.

WHAT CAUSES ATAXIA?

Ataxia is usually caused by damage to the cerebellum or to its connections. These connections are known as "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. 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 there are, as yet, no solid answers. In general, many researchers believe that the cerebellum receives sensory information from the entire body and a copy of the motor commands being sent to move the body. It integrates this information by using a densely interconnected network of nerves. These interconnections help 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. Presumably, this is done to 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 (an injury to a small 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. 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 symptoms that may simultaneously affect many functions of the cerebellum. In some cases, a child's cerebellum may not have formed properly. Often the symptoms are relatively mild, as other brain areas may take over some lost functions.

WHAT DISEASES ARE ASSOCIATED WITH ATAXIA?

Many diseases 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. Detailed information on diseases, disorders, medications, and conditions associated with ataxia may be found on the KidsMove Web site at www.kidsmove.org (KIDSMOVE--WORLDWIDE EDUCATION AND AWARENESS FOR CHILDREN'S MOVEMENT DISORDERS).

HOW IS ATAXIA DIAGNOSED AND EVALUATED?

The first feature that can be observed in cases of 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 whether there are variations in the severity of the symptoms during the day, such as:

* at mealtime;

* when the child is tired, hungry, or ill;

* after the child eats a particular type of food.

THE PHYSICIAN MAY ASK CERTAIN QUESTIONS 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 ended without treatment?

* If they come and go, how long do they last and do they ever become completely better?

Many types of ataxia are hereditary, so it is also important to look for subtle symptoms in family members including clumsiness, frequent falling, late walking, early speech issues, unusual eye movements, poor handwriting, or other neurological problems.

After listening to the history of the symptoms and examining the child, the physician may take several steps, depending on the particular circumstances. The first step is to address the question of 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 disorders. If it appears that the child has ataxia, further studies often include laboratory tests and imaging studies.

THE MOST COMMON INITIAL LABORATORY TESTS INCLUDE:

* Blood and urine for electrolytes, such as sodium, potassium, chloride, and bicarbonate

* Glucose

* Amino acids

* Organic acids

* Ammonia

* Copper

* Vitamin E

The most common initial imaging test is a brain magnetic resonance image (MRI) scan. This test enables the physician to look for structural abnormalities, tumors, or evidence of stroke. It is important to perform the MRI and initial tests during the early phase of evaluation as these tests may find causes for the ataxia that may require rapid treatment. In some circumstances, it may also be necessary to test for toxins, medication overdoses, or heavy metal poisoning, particularly lead, mercury, and thallium.

In some children, no cause for ataxia is found after the initial set of tests. In these cases, further metabolic and genetic tests may be performed. The choice of these tests is based on the child's age, symptoms, and family history. The most commonly tested genetic disorders include the spinocerebellar ataxias or SCAs, Friedreich's ataxia, and ataxia-telangiectasia (AT). If the child has myoclonus or myoclonic eye movements (opsoclonus) in addition to the ataxia, it is important for the physician to look for a neuroblastoma in the chest or abdomen, as these tumors may cause opsoclonus-myoclonus-ataxia syndrome.

CAN ATAXIA BE TREATED?

In some children, the metabolic disorders that cause ataxia may be treated with controlled diets and special medications. If the ataxia is due to a toxin, avoiding the toxin and other particular anti-toxin measures may be appropriate. If the ataxia is due to a tumor, then surgery may be necessary. If ataxia is due to a stroke, it is important to prevent further strokes and minimize the current injury.

Most other causes of ataxia do not have specific treatments, and there is no replacement for cerebellar cells that die or those cells that never developed properly. The most effective treatment often consists of physical therapy to train and strengthen muscles, thus helping to compensate for impaired muscle function. Gait and balance training may also be helpful. The use of a cane, crutches, or walker is often beneficial. In some cases, adapted utensils and other tools may be helpful. Speech therapy may sometimes be helpful for ataxic speech. Ataxia of eye movements rarely requires treatment.

For more information about neurologic movement disorders affecting children and young adults, visit www.kidsmove.org. KidsMove is WE MOVE's new Web site devoted to pediatric movement disorders. Healthcare professionals and parents may access up-to-date information about the recognition, assessment, treatment, and avenues of support that are available for individuals concerned with childhood movement disorders.

Terence D. Sanger, MD, PhD is the director of the pediatric movement disorders clinic at Lucille Packard Children's Hospital at Stanford University. He is a child neurologist and electrical engineer. His research laboratory investigates the detailed measurement of movement disorders in children, including ataxia, dystonia, chorea, myoclonus and spasticity.

Joy E. Bartnett, AMIA, AMWA, NASW is a medical writer and biomedical informatics specialist for WE MOVE, a not-for-profit organization committed to increasing worldwide education and awareness for movement disorders. WE MOVE has been educating and informing healthcare professionals, patients and the public about movement disorders since 1991.