Classification and Definition of Disorders Causing Hypertonia in Childhood

Abstract

This article defines "spasticity," "dystonia," and "rigidity" to describe hypertonia in children.
Definitions are designed to differentiate clinical features, even when multiple are present.
A consensus agreement was obtained on current definitions and application in clinical settings.

Definitions

Spasticity: Hypertonia with:
- Resistance to externally imposed movement increases with speed of stretch and varies with the direction of joint movement.
- Resistance rises rapidly above a threshold speed or joint angle.
Dystonia: Movement disorder with:
- Involuntary sustained or intermittent muscle contractions causing twisting, repetitive movements, or abnormal postures.
Rigidity: Hypertonia with all of the following:
- Resistance to externally imposed joint movement is present at very low speeds and does not depend on imposed speed, and does not exhibit a speed or angle threshold.
- Simultaneous co-contraction of agonists and antagonists, reflected in immediate resistance to reversal of movement direction.
- Limb does not tend to return to a particular fixed posture or extreme joint angle.
- Voluntary activity in distant muscle groups does not lead to involuntary movements about the rigid joints, although rigidity may worsen.
Definitions are intended to identify different components of childhood hypertonia.
Encourages clinical rating scales based on these definitions.
Encourages research relating hypertonia to functional ability, change over time, and societal participation.

Introduction

Abnormalities of tone are integral to chronic motor disorders in childhood.
Result from dysgenesis or injury to motor pathways in the:
- Cortex
- Basal ganglia
- Thalamus
- Cerebellum
- Brainstem
- Central white matter
- Spinal cord
Cerebral Palsy (CP) is often used if the injury occurs before the age of 2.
Childhood motor disorders are classified into hypertonic or hypotonic groups based on muscle tone.
Terms associated with hypertonia: "spasticity," "dystonia," and "rigidity."
Lack of general agreement on definitions exists in clinical situations.
Current definitions are based on adult disorders and spinal cord injury, leading to inconsistent labeling of pediatric symptoms.
Studies of rehabilitative interventions are hampered by difficulty in establishing homogeneous cohorts due to varying classification systems.
Imprecision exists in classifying tone abnormalities and categorizing functional impairments.
A clear and consistent set of definitions is needed for communication between clinicians and selection of children for therapy and research trials.
The ultimate purpose is to minimize disability and promote independence and full participation in society for children with motor disorders.
Treatment goals mirror management of other chronic diseases.
World Health Organization separates chronic diseases into:
- Impairment
- Functional ability
- Societal participation
The National Center for Medical Rehabilitation Research model encompasses 5 axes:
- Pathophysiology (underlying disease)
- Impairment (clinically observable abnormality)
- Functional limitations (effect on task performance)
- Disability (effect on daily living)
- Societal limitations (effect on lifetime opportunities)
Major obstacles in evaluation include limitations of measurement tools and lack of objective criteria.
This article provides specific clinical definitions of 3 types of hypertonia that are thought to cause specific impairment of movement.
The goal is to build a foundation for understanding how childhood hypertonia relates to other impairments and its impact on function, disability, and societal participation.

Goals of Definitions

Reliable communication between clinicians.
Accurate distinction of diagnostic groups for clinical research.
Appropriate selection of patients for medical or surgical interventions.

Criteria for Definitions

Utility: Easy testing in a routine clinical setting to differentiate spasticity, dystonia, and rigidity, with eventual confirmation by quantitative methods.
Reliability: Consistent labeling by different examiners (interobserver) and by the same examiner at different times (intraobserver).
Validity: Agreement with expert assessments (face validity), prediction of quantitative measurements (criterion validity), and prediction of therapy response (construct validity).
Definitions draw on current knowledge of neuromuscular systems and data from objective measures.
Hypertonia may be due to a wide range of underlying pathophysiology and is associated with varying degrees of impairment, functional limitations, disability, or societal limitations.
Multiple types of hypertonia may be present in the same child.
Clinical usage divides motor disorders into pyramidal and extrapyramidal types.
These terms have historical bases and clinical utility but are highly interconnected and interdependent.
Pyramidal motor disorders result from injury to the corticofugal projections to the brainstem (corticobulbar) and spinal cord (corticospinal).
- Corticospinal tracts were previously believed to be responsible for all aspects of the motor dysfunction, but recent evidence suggests that other regions must be involved.
- Injury to these pathways often is associated with a combination of weakness and increased stretch reflexes.
- The weakness often occurs in a particular pattern referred to as “pyramidal” or “upper motoneuron” weakness.
- The pattern of pyramidal weakness can be position and state-dependent.
Extrapyramidal motor disorders result from injury to the basal ganglia, cerebellum, or non-primary motor cortical areas.
- Often leads to abnormal motor control without weakness or changes in spinal reflexes.
- In children, both pyramidal and extrapyramidal motor disorders are most commonly seen as part of the syndrome of CP.
Commonly used classification schemes of CP divide the disorders into pyramidal (spastic) and extrapyramidal (dystonic, athetoid) types, but it is widely recognized that most children with CP have both pyramidal and extrapyramidal features.
The coexistence of pyramidal and extrapyramidal signs can make determination of the relative contributions of these systems complex, because types of hypertonia including spasticity, rigidity, and dystonia often are present simultaneously.
The complexity of the motor syndromes is superimposed on the unique process of growth (increase in size) and development (maturation of the central nervous system and acquisition of new skills through learning).
Because of growth and developmental plasticity, a static injury to the central nervous system may lead to a dynamically changing clinical picture that can be described as nonprogressive but ever-changing.
Thus, children present unique challenges for diagnosis.

Hypertonia

Innervated muscle exhibits viscous and elastic properties such that force is required to stretch a muscle from its resting position.
The components of this muscle force include:
1. The force generated by initially active muscle fibers.
2. The force attributable to stretch reflex action.
3. The force attributable to passive tissue properties.
Accordingly, for clinical use, tone is defined operationally as resistance to passive stretch while the patient attempts to maintain a relaxed state of muscle activity.
Tone in part reflects the state of active muscle contraction and may be increased or decreased at rest.
The definition of tone explicitly excludes resistance as a result of joint, ligament, or skeletal properties such as those that may occur with fixed deformities, including connective tissue disease or joint contractures.
In many cases, such deformities can be distinguished from neuromuscular tone and they are not classified as hypertonia (examination during sleep or under anesthesia may be helpful in distinguishing such deformities).
Tone is assessed clinically using passive movements about a joint to determine muscular resistance.
By our definition, tone is perceived by an examiner but not directly perceived by the patient.
Assessment should include palpation of muscles to estimate the resting (baseline) state of muscle activation.
Note, however, that tone is not rated by the presence or absence of muscle contraction at rest.
Instead, our definition of tone requires an externally imposed movement to make the assessment.
Tone may be measured in muscles that are at rest or in those with involuntary active contraction, but it should not be measured during voluntary muscle contraction.
Hypertonia is defined as abnormally increased resistance to externally imposed movement about a joint.
It may be caused by spasticity, dystonia, rigidity, or a combination of features.
We encourage the use of the terms spastic hypertonia, dystonic hypertonia, or rigid hypertonia to distinguish the primary feature.
When hypertonia is so severe that imposed joint movement is not possible, then this subclassification cannot readily be performed.
Mechanisms that lead to increased tone may also contribute to poor voluntary motor performance or involuntary muscle contractions, but assessment of tone is independent of strength, dexterity, coordination, or involuntary movements.

Spasticity

Emphasis on the difference between passive muscle tone in clinical examination and impairment of voluntary movement.
Spasticity is defined in terms of clinical examination features, recognizing that disability is related to associated deficits like weakness or lack of coordination.
*Spasticity is a velocity-dependent resistance of a muscle to stretch.
Spasticity is defined as hypertonia where:
1. Resistance to externally imposed movement increases with increasing speed of stretch and varies with the direction of joint movement.
2. Resistance to externally imposed movement rises rapidly above a threshold speed or joint angle.
Increased resistance specified in the first criterion is usually not directly proportional to the speed of stretch.
The resistance must be different for high versus low speeds of passive movement and for flexion versus extension about the joint.
The second criterion defines a feature of the “spastic catch”.
The velocity dependence and threshold of the catch may reflect the stretch reflex threshold with initial recruitment of previously quiescent motoneurons.
The threshold behavior might then be determined by the excitability of the motoneurons being assessed and by the starting length of the muscle.
In this case, if motoneurons are highly excitable and if the muscle is stretched from an elongated initial position, then reflex threshold may be reached almost immediately, and a catch may not be evident.
Spasticity can vary depending on a child’s state of alertness, activity, or posture, as well as, anxiety, emotional state, pain, surface contact, or other nonnoxious sensory input.
Spasticity may worsen with movement of the involved muscles or maintenance of the limb against gravity, but it is not specific to particular attempted tasks.
The terms spasticity and spastic hypertonia may be used interchangeably.
Electrophysiological studies show changes in the threshold of the tonic stretch reflex with increased resistance as passive speed increases.
The increased tone may be attributable to the reflex component of muscle elasticity and changes in muscle mechanical properties.
Spasticity may be accompanied by a transformation of motor units, such that tension development occurs with lower levels of electromyograph activity, potentially improving weight-bearing efficiency.
Spasticity may either worsen or improve motor disability.
Spasticity depends on afferent feedback of proprioceptive information from muscle, joint, and skin receptors.
Spasticity often coexists with other motor symptoms.
The multiple meanings of the term “spasticity” have led to significant confusion.
The term "upper motor neuron syndrome” refers to the clinical finding of spasticity plus:
1. Hyperreflexia with or without clonus
2. Reflex overflow
3. Presence of a Babinski response
4. Weakness that may primarily affect lower extremity flexor or upper extremity extensor muscle groups (“pyramidal distribution” weakness).
Confirming the distribution of weakness requires voluntary cooperation by the child.
Damage to the tracts that project to the lower motor neurons of the spinal cord does not in general lead to the findings listed above.
Elements of the upper motor neuron syndrome can be divided into positive (hyperreflexia, overflow, and Babinski response) and negative (weakness, loss of dexterity) components.
Positive symptoms are associated with the release of the intact motor system from control.
Negative symptoms may be linked with the loss of a specific skill of central nervous system origin.
Incoordination, loss of selective motor control, poor motor planning, and abnormal muscle activation patterns may occur but cannot be easily differentiated from findings attributable to co-existing ataxia or dystonia.
The asymmetric tonic neck reflex is commonly present but may not be specifically related to spasticity.
It is unclear the extent to which components of the upper motor neuron syndrome may represent the persistence or release of normally suppressed primitive or early developmental patterns of muscle activation.

Dystonia

Dystonia is an involuntary alteration in the pattern of muscle activation during voluntary movement or maintenance of posture.
Diagnosed by the observation of abnormal twisted postures or repetitive movements.
Dystonia in childhood is defined as a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both.
Dystonia is commonly triggered or exacerbated by attempted voluntary movement and may fluctuate in presence and severity over time.
The severity and quality of dystonic postures may vary with body position, specific tasks, emotional state, or level of consciousness.
Dystonia is not always present in hypertonia.
Dystonia may lead to sustained involuntary muscle contraction only during attempts at voluntary movement, with normal or decreased tone and muscle activity when measured at rest.
If dystonia is present at rest and causes an involuntary posture, then it may be a cause of hypertonia.
The term dystonic hypertonia is encouraged to be used for the above condition.
Hypertonia caused by dystonia results from tonically contracting muscles that contribute to passive joint stiffness.
Dystonia is a cause of hypertonia only when there is muscle activity when the child is at rest and the limb is supported against gravity, or when muscle activity begins before the onset of externally imposed passive joint movement.
To diagnose dystonic hypertonia, there must be observable dystonic postures that do not relax during the examination of tone.
The body part being examined must be supported against gravity to ensure that postural muscle activity is not contributing to the apparent tone. In dystonic hypertonia, there is:
1. Resistance to externally imposed joint movement is present at very low speeds of movement, does not depend on imposed speed, and does not exhibit a speed or angle threshold.
2. Simultaneous co-contraction of agonists and antagonists may occur, and this is reflected in an immediate resistance to a rapid reversal of the direction of movement about a joint.
3. The limb tends to return toward a fixed involuntary posture, and when symptoms are severe, the limb tends to move toward extremes of joint angles.
4. Hypertonia is triggered or worsened by voluntary attempts at movement or posture of the affected and other body parts and may be strongly dependent on the particular movement or posture attempted or the activity of distant muscle groups.
5. The pattern as well as the magnitude of involuntary muscle activity varies with arousal, emotional and behavioral state, tactile contact, or attempted task.
6. There is no other detected spinal cord or peripheral neuromuscular pathology causing tonic muscle activation at rest.
These are features of dystonia when it causes hypertonia, but these features are not part of the definition of dystonia per se.
Dystonia may be subclassified as action induced or posture induced.
- In adults, the actions that lead to dystonia may be restricted to certain attempted tasks, although task specificity is less common in children.
- When dystonia is present at rest or with posture, certain attempted postures may be impossible to attain.
Dystonia may be triggered or worsened by attention, distraction, startle, overuse, fatigue, touch, or pain.
It is often exquisitely sensitive to postural and anti-gravity control, and it must therefore be tested seated, standing, supine, and with nearby joints in both flexion and extension.
Dystonia is not necessarily a primary disorder of tone but may seem to be because of the inability to relax the muscles fully.
Dystonia and spasticity may occur in the same limb, and distinction requires determining the velocity-dependent, action-induced, and posture-responsive components.
It may be difficult to distinguish dystonia from extensor posturing of the lower extremities, particularly when the extensor posturing is triggered by muscular effort.
It may also be difficult to evaluate for spasticity in a muscle that is initially active as a result of dystonia because the motoneuron pools may be in a suprathreshold state before the onset of externally imposed movement.
When both spastic and dystonic hypertonia occur together, this is referred to as mixed hypertonia.
In children, mixed hypertonia may be more common than either pure dystonic or pure spastic hypertonia.
The term mixed hypertonia is preferred to older terms such as spastic dystonia or dystonic spasticity.
Dystonia may be limited to specific regions of the body, leading to a more specific dystonic syndrome, such as writer’s cramp, blepharospasm, torticollis, or opisthotonus.
The location of dystonia is characterized as:
- Focal– single body part
- Segmental– 1 or more contiguous body parts
- Multifocal– 2 or more noncontiguous body parts
- Generalized - 1 Leg and the trunk plus one other body part OR both legs plus one other body part.
- Hemidystonia– one half the body.
Children with dystonia commonly have other features, including athetosis, poor dexterity, and abnormal patterns of muscle activation.
Eye movement and oromotor abnormalities are frequently associated, but these features do not distinguish dystonic hypertonia from other causes of hypertonia.
The anatomic localization of lesions that lead to dystonia has not yet been identified with certainty.
It is likely that many forms of childhood dystonia are attributable to lesions in the basal ganglia.

Rigidity

Rigidity is a common movement disorder in adults, frequently diagnosed as a feature of parkinsonism, but only rarely reported in children.
It is unknown whether the apparent rarity of parkinsonian rigidity in children is attributable to underrecognition or to low incidence.
Some practitioners use the term “rigid” to refer to any joint that cannot be moved.
The use of a more specific definition is encouraged, in which the resistance to passive movement is independent of posture and speed of movement.
The adjective “lead-pipe” is advocated to be used rather than “parkinsonian” or “cogwheel” to avoid erroneous inferences.
Like spasticity and dystonia, rigidity may be dependent on the state of the child.
Unlike dystonia, rigidity is not specific to particular tasks or postures.
In adults with Parkinson’s disease, rigidity may result from baseline muscle contraction, hyperactive long-latency stretch reflexes, or both.
There has been relatively little investigation of the features of rigidity in children; therefore, the following definition is based on experience with adults.
Rigidity is defined as hypertonia in which all of the following are true:
1. The resistance to externally imposed joint movement is present at very low speeds of movement, does not depend on imposed speed, and does not exhibit a speed or angle threshold.
2. Simultaneous co-contraction of agonists and antagonists may occur, and this is reflected in an immediate resistance to a reversal of the direction of movement about a joint.
3. The limb does not tend to return toward a particular fixed posture or extreme joint angle.
4. Voluntary activity in distant muscle groups does not lead to involuntary movements about the rigid joints, although rigidity may worsen.
The terms rigidity and rigid hypertonia may be used interchangeably.
The distinction from dystonic hypertonia is based on the lack of an associated abnormal posture or extreme position of the joint.
This distinction may also be supported by the finding of a lack of muscle activity at rest.
In rigidity, muscle activity is brought on by the externally imposed movement.
Hypertonia as a result of rigidity is usually not as sensitive to changes in posture.
Rigidity may be worsened by movement of distant or contralateral muscles, an effect referred to as “activated rigidity.”
Rigidity as defined here is different from the finding of a stiff, immovable, or “rigid limb” that may be attributable to contractures, spasticity, dystonia, or rigidity as defined here.
The use of the term rigidity only in the more specific sense defined in this article is encouraged.
Rigidity may be associated with bradykinesia, tremor, flexed posture, and gait instability, leading to the syndrome of juvenile parkinsonism.
Rigidity may be attributable to disorders of dopaminergic transmission or basal ganglia function, but the present definition does not include an implied localization.

Other Forms of Hypertonia

Resistance to passive movement as a result of disorders of spinal cord, peripheral nerve, muscle, or connective tissue, startle syndromes, stiff person syndrome, α-motoneuron dysfunction, myotonia, neuromyotonia, myokymia, and others are not addressed in this article.
Other childhood movement disorders such as athetosis, chorea, ataxia, the hyperkinetic features of dystonia, myoclonus, tremor, and tic disorders are not addressed in this article.

Recommended Technique for Clinical Evaluation of a Hypertonic Joint

Clinician should elicit parents’ description of abnormal tone and involuntary movements.
Observe posture at rest and position of limbs with respect to gravity.
Observe the child lying, sitting, walking, and running, if possible. If complaints include abnormal performance or postures in response to specific activities or tasks, then the child should be observed while performing the affected task.
Note any abnormal fixed, twisted, or repetitive posture and the degree of functional limitation.
The child should be relaxed as much as possible during the examination, and the body part being examined should be supported against gravity.
The head should be maintained in the midline to avoid contributions to tone from the tonic neck reflex.
If lying supine, then the head and trunk should be resting comfortably.

Palpate the muscles to determine whether contraction occurs at rest.
Measure resistance to movement of the affected joint with the child supine, seated, and standing, if possible, as well as while distracted.
Measure passive range of motion at very slow (3 seconds to complete the movement), intermediate (0.5 second to complete the movement), and fast (as rapidly as possible) speeds. Note the resistance at the onset of movement, the presence or absence of a “catch” occurring at some time after the onset of movement, and the joint angle at which the catch occurs.
Perform sudden reversal in the direction of movement at slow, intermediate, and fast speeds, and note the presence or absence of increased resistance immediately on reversal (suggesting co-contraction) or at some time after (suggesting a spastic catch), as well as any velocity dependence.
Instruct the child to move the same joint on the contralateral side and observe for involuntary movement, then test for a change in resistance to slow, passive movement. Instruct the child to move a distant and unrelated joint (eg, by opening and closing 1 fist) on the contralateral side and then the ipsilateral side, and observe for involuntary movement or a change in resistance to passive movement.

Recommended Technique for Determination of the Elements That Contribute to Hypertonia

If there is variation in hypertonia with the speed of externally imposed movement or if a catch occurs above a threshold velocity, then spastic hypertonia is present.
If the affected limb returns to a specific posture, there is muscle activity at rest in the absence of imposed movement, and the severity of hypertonia varies significantly with the child’s movement, position, or behavioral state, then dystonic hypertonia is present.
If muscle activity increases with externally imposed movement, the same amount of resistance to movement occurs at any speed of stretch, resistance to movement occurs at arbitrarily low speeds, and there is no consistent abnormal posture, then rigid hypertonia is present.
Spastic hypertonia is distinguished from dystonic or rigid hypertonia by the increase in resistance at high imposed speeds of movement.
Dystonic hypertonia may be distinguished from rigid hypertonia by the presence or absence of muscle contraction at rest, although this finding has not been consistently verified.
When dystonic and rigid hypertonia are simultaneously present, the rigid component can be measured when there is an initial posture in which the muscles are at rest so that the dystonic component is eliminated.
When spastic hypertonia is also present, dystonic or rigid components are distinguished from spasticity by the resistance to slow imposed speeds of movement.

Measures of Severity

Most current scales do not distinguish between diagnostic categories, but may be useful once a category has been assigned.
Scales include: the pendulum test, the modified Ashworth scale, and others.
Tardieu scale explicitly compares the occurrence of a catch at low and high speeds and is effective in measuring the velocity-dependent component of hypertonia.
Other measures may be useful for rating severity of dystonia and rigidity:
- Barry-Albright Dystonia scale
- Burke-Fahn-Marsden dystonia rating scale
- Unified Dystonia Rating Scale
- Unified Parkinson’s Disease Rating Scale
Quantitative kinematic and electromyelogram analysis provides an additional set of methods for determining the severity of clinical findings.

Measures of Functional Ability

Increased tone may have a variable relationship to functional limitation or disability.
In many cases, increased tone permits greater functional ability in a child with underlying weakness, and this may be particularly true for mobility.
Conversely, severe hypertonia can be associated with severe disabling joint contractures.
Hypertonia may also be associated with pain, and it may be difficult to separate any restriction as a result of the primary handicap from possible restriction as a result of pain.
In addition to assessing the presence and severity of hypertonia, it is important to assess the child’s functional abilities.
Functional abilities may be affected by the following components of function- sensory processing, cognitive abilities, alertness, and others.
Quantifiable measures include:
- Pediatric Evaluation of Disability Index
- Peabody Developmental Motor Scale
- Bayley Scales of Infant Development
- Functional Independence Measure for Children
- Gross Motor Function Measure
- Test of Infant Motor Performance
- Child Health Questionnaire
Scales are not designed to distinguish between diagnostic categories, and very different disorders and symptoms may lead to similar scores of functional ability.
It will be important in the future to establish whether different forms of hypertonia and tone abnormalities affect the person’s functional abilities and quality of life in different ways.
Adequate treatment should not be restricted to the correction of specific clinical features but should instead be based on the functional limitations that are of direct concern to the patient.

Future Goals

An important next step is to develop rating scales that are based on these definitions.
- Scales are needed both to quantify the degree of increased tone and to distinguish between the different types of increased tone.
- Such scales will most likely be modifications of 1 or more of the many existing scales intended for this purpose.
- Essential to determine the utility, validity, and reliability of such scales.
- Important component of validation of the scales- determine the extent to which any measure of increased tone correlates with the degree of functional impairment.
- It will also be important to determine whether definition and distinction of the different types of hypertonia and their causes in fact lead to clinically significant changes in the management of patients.
There may be only a weak relationship between the physical signs obtained during the clinical examination in a passive motor condition and the impaired neuronal mechanisms in operation during an active movement.
It is hoped that through the recording and analysis of electrophysiological and biomechanical parameters during a functional movement such as locomotion, the significance of impaired reflex behavior or pathophysiology of muscle tone and its contribution to the movement disorder can reliably be assessed.
Therefore, at the same time as clinical rating scales are developed, it is essential to validate quantitative and physiologic measures of function.
- Such measures can include kinematic and dynamic analysis, electrophysiology, and neuroimaging.
- These measures would need to be validated by comparison with clinical measures and ultimately determination of functional outcomes.

Necessary Steps for Continuing Study of Childhood Motor Disorders

Development of impairment rating scales based on the definitions given here.
Development of definitions and rating scales for other childhood motor impairments, including athetosis, chorea, ataxia, the hyperkinetic features of dystonia, myoclonus, and tremor.
Assessment of the utility of the rating scales in terms of their ease of application in a clinical setting and the ability to detect changes in hypertonia over time.
Evaluation of the interrater and intrarater reliability for diagnosis of hypertonia as well as for determining the relative severity of spasticity, dystonia, and rigidity.
Validation of the rating scales against current clinical judgment, electrophysiological measures, quantitative biomechanical measures, and neuroimaging modalities.
Validation of the rating scales against functional outcome measures to determine the extent to which hypertonia causes functional limitations and in which situations resolution of hypertonia leads to reduction of disability.
Determination of the ability of the rating scales to predict the response to therapy.
Determination of the ability of the rating scales to select appropriate patients for different therapeutic options.
Selection of standardized rating scales for childhood functional limitation, disability, and societal participation, with the choice of appropriate scale based on the child’s functional ability and degree of impairment.

There is increasing evidence that sensory systems may be abnormal in children and adults with movement disorders.
- In particular, abnormalities of proprioception and tactile sensation could potentially contribute to worsening symptoms and might be amenable to new treatment options.
- Research is encouraged to determine the extent to which sensory involvement is present in childhood disorders and how it contributes to hypertonia and the success of intervention.
clinical treatment trials will frequently need to be performed between multiple clinical centers to obtain a sufficiently large and homogeneous population for testing because of the wide range of causes and symptoms in children with motor disorders.
This article is intended to provide an initial foundation for discussion of hypertonia in childhood by focusing on definitions of terms and syndromes.
The ultimate goal is to provide a reliable method to characterize hypertonia and to establish effective treatment options for affected children.