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Hypertonicity


Definitions

Tone is defined as resistance to passive stretch while a patient is attempting to maintain a relaxed state of muscle activity. Tone can be divided into postural tone, which represents the steady flexion or extension of a joint caused by the uniform resistance of muscle to passive movement, and phasic tone, which represents the catch when an extremity is rapidly flexed or extended. Hypertonia describes unusually elevated tone, typically the result of an upper motor neuron disease. Hypertonia itself has three different clinical subtypes that may exist individually or in combination ( Table 38.1 ):

    • Spasticity : hypertonia in which one or both of the following signs are present: (1) resistance to externally imposed movement increases with increasing speed of stretch and varies with the direction of joint movement, and/or (2) resistance to externally imposed movement rises rapidly above a threshold speed or joint angle.

    • Dystonia: movement disorder in which involuntary, sustained, or intermittent muscle contractions cause twisting and repetitive movements, abnormal posture, or both. The muscle contractions are the hypertonic component.

    • Rigidity: 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; and (4) voluntary activity in distant muscle groups does not lead to involuntary movements about the rigid joints, although rigidity may worsen.

TABLE 38.1
Clinical Findings of the Different Hypertonia Subtypes
Clinical Finding Spasticity Dystonia Rigidity
Change in resistance with increasing speed of passive movement Increases No effect No effect
Change in resistance with rapid reversal of direction Delayed Immediate Immediate
Fixed posture Only in severe cases Yes No
Effect of voluntary activity on pattern of activated muscles Minimal Yes Minimal
Effect of behavioral task and emotional state pattern of activated muscles Minimal Yes Minimal

The term motor syndrome is an alternative term inclusive of the different types of clinical hypertonia as well as other neurologic deficits. A motor syndrome caused by an injury before the age of 2 years is often labeled cerebral palsy (CP), whereas motor syndromes caused by injuries sustained after that age are described by terminology typically related to the etiology.

CP (see Chapter 27 ) and dystonia syndromes (see Chapter 40 ) are the two most common etiologies of hypertonia in children.

History

Elements of the history that should be collected include:

  • Onset of increased tone

  • Preceding illnesses, traumas, surgeries, or any events prior to the onset of increased tone

  • Course of hypertonia including worsening, improvement, or no changes over time since the onset

  • Limbs or body parts affected including the part most prominently affected

  • Any times of the day when hypertonia is most or least noticeable

  • Abnormal posture or movements

  • Abnormal gait

  • Worsening and alleviating factors

  • History of brain or spinal cord injuries

  • Drug or toxin exposure

  • Pregnancy and birth

  • Other medical or surgical conditions

  • Family history of any neuromuscular disorders

  • Environmental or medical allergies

Physical Examination

A general physical examination includes head and neck, cardiopulmonary, abdominal, skin, and genital examinations. Findings on any of these areas may indicate a syndromic or genetic pathology. Additionally, abnormalities in these systems may have implications on treatment options for hypertonicity.

The neurologic examination includes the following components:

    • Mental state: This is age dependent and can range from observing the patient interacting with their environment and people around them in the first few years of life to formal mental state testing in the older cooperative child.

    • Cranial nerves examination includes pupillary reflexes, external eye movements, facial sensation, face symmetry, hearing, tongue and uvula on the midline, neck movements, and shoulder shrug.

    • A fundoscopic examination should be performed whenever possible. Abnormal findings in the retina can be signs of a genetic or systemic pathology or an intracranial pathology leading to increased intracranial pressure.

The motor examination is the main tool to assess a patient with hypertonia. Components of the motor exam include:

    • Strength: The ability to examine strength is also dependent on the patient’s age and cooperation and ranges from observing the child moving their limbs against gravity and the examiner’s resistance to the more detailed exam of different muscle groups in the child who is able to follow commands. Strength is typically graded as follows: 0: no contraction or movement; 1: muscle contraction but no movement; 2: movement at the level of the bed but not against gravity; 3: movement against gravity but not against resistance; 4: some movement against resistance but not at the expected full level for age; and 5: normal movements against resistance.

    • Muscle bulk is assessed by inspection and palpation to detect any subtle muscle wasting, fasciculations, or hypertrophy.

    • Tone: It is important to take a thorough look at the whole musculoskeletal system in a child presenting with increased tone, including the parts that are reportedly unaffected. This allows for comparison and detection of any unreported abnormalities by history. Inspection will look for size of the muscles, abnormal posture, and abnormal movements.

The child should be relaxed as much as possible and the body part examined supported against gravity. The head should be maintained in the midline to avoid contributions to tone from the tonic neck reflex. The following steps are then performed:

  • 1.

    Palpate muscles to look for contraction at rest.

  • 2.

    Measure resistance to movement of the affected joint with the child supine, seated, and standing.

  • 3.

    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.

  • 4.

    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.

  • 5.

    Ask the child to move the same joint on the contralateral side and observe for involuntary movement, and then test for a change in resistance to slow, passive movement. Instruct the child to move a distant and unrelated joint (e.g., by opening and closing one fist) on the contralateral side and then the ipsilateral side and observe for involuntary movement or a change in resistance to passive movement.

Reflexes: The main reflexes examined are the biceps, triceps, brachioradials, ankles, and knees.

Gait: When applicable, gait can aid in the determination of the different deficit patterns related to weakness, hypertonia, or movement disorders affecting the lower limbs.

Different scaling systems have been developed to measure hypertonia including the Ashworth, modified Ashworth, and pendulum tests. These tests do not distinguish between the different clinical types of hypertonia but do measure severity. The Tardieu Scale compares the occurrence of a catch at low and high speeds and is effective in measuring the velocity-dependent component of hypertonia ( Table 38.2 ). Other scales are designed to specifically measure dystonia and rigidity such as the Barry-Albright Dystonia Scale. The Hypertonia Assessment Tool (HAT) is a 7-item scaling system designed to assess all three different types of hypertonia for each extremity and has been shown to have good reliability, validity, and inter-rater agreement in identifying spasticity and the absence of rigidity, and moderate findings for identifying dystonia ( Table 38.3 ).

TABLE 38.2
Comparison of Ashworth and Tardieu Hypertonia Scales
Ashworth Scale Tardieu Scale
0 No increased tone No resistance
1 Slight increase in muscle tone, manifested by a catch and release or by minimal resistance at the end of the range of motion when the affected part is moved in flexion or extension Slight resistance
2 More marked increase in muscle tone through most of the range of motion, but affected part(s) easily moved Catch followed by a release
3 Considerable increase in muscle tone, passive movement difficult Fatigable clonus (<10 sec)
4 Affected part(s) rigid in flexion or extension Infatigable clonus (>10 sec)

TABLE 38.3
Hypertonia Assessment Tool (HAT) with a Description of the Administration Procedure for Each Item
From Jethwa A, Mink J, Macarthus C, et al. Development of the hypertonia assessment tool (HAT): a discriminative tool for hypertonia in children. Dev Med Child Neurol . 2010,52:e83–e87 (Appendix I, p. e87).
Items (in Order of Administration) Type of Hypertonia Administration of Item Scoring (Fill Each Box with 0 [Negative] or 1 [Positive])
Increased involuntary movements or postures of the designated limb with tactile stimulus of a distant body part Dystonia With the child at rest, observe involuntary movements of the designated limb as you gently rub a distant body part such as the shin or forearm Dystonia is present if more involuntary movements or postures are observed in the designated limb with the tactile stimulus
Increased involuntary movements or postures with purposeful movement of a distant body part Dystonia Observe movements of the designated limb as the child carries out purposeful movements ∗ Dystonia is present if more involuntary movements or postures are observed in the designated limb with purposeful movement
Velocity-dependent resistance to stretch Spasticity Move the limb as described below † and assess for a change in muscle resistance between the slow and the fast stretch Spasticity is present if there is an increase in resistance between the fast stretch compared with the slow stretch
Presence of spastic catch Spasticity Note the presence of a rapid rise (spastic catch) in resistance at a particular joint angle when moving the limb as described during the fast stretch † Spasticity is present if a spastic catch is noted
Equal resistance to passive stretch during bidirectional movement of a joint Rigidity Assess this item during the fast stretch of the muscle † Rigidity is present if the resistance felt is equal with movement in both directions
Increased tone with movement of a distant body part Dystonia Perform two additional fast stretches. † During the second stretch ask the child to do a purposeful movement ∗ and assess for an increase in tone Dystonia is present if greater tone is noticed when child is carrying out the purposeful movements
Maintenance of limb position after passive movement Rigidity For the arm, note the original position of the elbow; move the elbow by 45 degrees into either flexion or extension and observe if the elbow returns to its original position. For the leg, note the original position of the ankle; move the ankle into 45-degree further dorsiflexion or plantarflexion and observe if the ankle returns to its original position Rigidity is present if the limb remains in the final position of stretch rather than returning (partially or fully) to the limb’s original position
Before administering the HAT, the child should be supine on the examining table. The child should be as comfortable as possible by having appropriate caregivers present, a roll placed under the knees, a comfortable room temperature, and unrestrictive clothing. Complete all items for the involved extremity being examined before moving on to the next involved extremity.

∗ Based on the child’s ability, ask the child to carry out two of the following for a 10-second period: (1) count to 10 slowly; (2) open and close one hand (into a fist) repeatedly (choose the hand that is not being examined); (3) open and close eyes (tight blinking) repeatedly; (4) reach for an object placed at least 1 foot away; and (5) visually track a brightly colored object (e.g., red-tipped pen) or light source (e.g., flashlight).

† Support the limb against gravity. Move the joints of the limb through the child’s full range starting with the joint in full flexion or adduction, moving to full extension or abduction, and then returning to flexion or adduction, twice slowly and twice as quickly as possible. Upper extremity: shoulder adduction and abduction—begin with shoulder in full adduction; elbow flexion and extension—begin with elbow in full flexion; forearm pronation and supination—begin with forearm in full pronation; wrist flexion and extension—begin with wrist in full flexion. Lower extremity: hip adduction and abduction—begin with hip in full adduction; knee flexion and extension—begin with knee flexed with the hip in 90-degree flexion; ankle dorsiflexion and plantarflexion—begin with ankle in full plantarflexion.

Etiology

Hypertonia is a result of a pathology to the upper motor neuron pathways in the cortex, basal ganglia, thalamus, cerebellum, brainstem, central white matter, or spinal cord. Hypertonia is not considered to be a sign of a peripheral nerve or muscle pathology.

Hypertonia is a component of many motor disorders. Clinically, motor disorders are often divided into pyramidal and extrapyramidal groups. However, it is increasingly recognized that the pyramidal and extrapyramidal motor systems are highly interconnected and a clear distinction is not always possible; rather, pathology affecting both systems usually exists in the same patient.

Pyramidal motor disorders result from injury to the cortical projections to the brainstem (corticobulbar) and spinal cord (corticospinal) at any point along their tract resulting in a combination of weakness and increased tendon reflexes.

Extrapyramidal motor disorders result from injury to the basal ganglia, cerebellum, or nonprimary motor cortical areas resulting in abnormal motor control without weakness or changes in tendon reflexes.

The coexistence of pyramidal and extrapyramidal signs can make determination of contributions of these systems complex because different clinical types of hypertonia (spasticity, dystonia, and rigidity) often coexist in the same patient to variable degrees.

Furthermore, the ongoing growth, maturation, and prominent plasticity of the central nervous system in children add to the complexity of motor syndromes, which can lead a static injury to the central nervous system to manifest with a dynamically changing clinical picture.

Cerebral Palsy

The most common disorder manifesting primarily with hypertonia in children is CP, resulting from an injury to the developing brain before the age of 2 years.

The different subtypes of spastic CP reflect the different variables involved in determining the clinical picture including age, location, and type of injury ( Table 38.4 ).

TABLE 38.4
Clinical Features of Spastic Cerebral Palsy (CP) Subtypes
CP Subtype Location of Hypertonia Common Causes and Location of Injury Age Group Clinical Features
Spastic diplegic Both lower limbs and upper limbs relatively or completely preserved Periventricular leukomalacia
Deep white matter		 Preterm infants Hypotonia of the lower limbs for the first 6 mo of life
Spasticity evolves by 6 mo of age
Flexion, adduction, and internal rotation of the hips with contractures of the hip flexors and hamstring muscles and to a lesser extent knees and elbows
Reduced limb length and muscle bulk in lower extremities
Spastic hemiplegic Hemibody including upper and lower limbs Neonatal stroke, congenital malformations
Cerebral cortex		 Term infants of normal birthweight Weakened and abnormal posturing on one body side
Early hand dominance
During first 1–2 yr, movement and tone on the affected side typically decrease before tone and tendon reflexes abnormally increase
The arm is typically more affected than the leg
Typical posture appears by 2 yr of age
Arm is adducted at the shoulder and flexed at the elbow, the forearm is pronated, and the wrist and fingers are flexed with the hand closed
Hip is partially flexed and adducted, and the knee and ankle are flexed; the foot may remain in the equinovarus or calcaneovalgus position
Independent walking usually occurs at the appropriate age or is only slightly delayed
Spastic quadriplegic All limbs affected Congenital infections, congenital malformations, ischemic hypoxic encephalopathy
Diffuse, cortical, and white matter injury		 Most commonly term SGA infants, but can also occur in preterm infants Moderate or severe psychomotor delay
All limbs are affected
Poor head control
Early spasticity by 2–3 mo of age
Adduction of the thighs results in typical scissoring of the legs
By 9–10 mo of age, unable to flex the legs with poor truncal balance
Upper limbs equally or more involved than lower limbs
Severe comorbidities including feeding difficulties, chronic respiratory insufficiency, and epilepsy are common
SGA, small for gestational age.

The overall prevalence of CP is ∼2 per 1,000 live births, with much higher prevalence in preterm compared with term infants and decreasing gestational age (GA) and birthweight (BW).

Although infants born preterm are at higher risk of developing CP, most CP cases are in infants born after 36 weeks’ GA. Of the overall CP cases, ∼25% are very preterm (GA <32 weeks), ∼10–20% moderately preterm or late preterm (GA 32–36 weeks), and ∼60% term (GA >36 weeks).

An approach to neonatal hypertonia is noted in Figure 38.1 .

Fig. 38.1, A suggested algorithm for the investigation of neonatal hypertonia. AGS, Aicardi-Goutières syndrome; aEEG, amplitude integrated EEG; CGH, comparative genomic hybridization; CSF, cerebrospinal fluid; EMG, electromyography; HIE, hypoxic-ischemic encephalopathy.

There are a number of genetic and metabolic disorders that present with clinical features of CP ( Tables 38.5 and 38.6 ). Hereditary spastic paraplegia is discussed in Chapter 27 .

TABLE 38.5
Brain MRI Findings Suggestive of Selected Genetic Cerebral Palsy Mimics
Adapted from Pearson TS, Pons R, Ghaoui R, et al. Genetic mimics of cerebral palsy. Mov Disord . 2019;34(5):625–636.
Finding Selected Conditions
Hypomyelination PLP1 -related dysmyelinating disorders
H-ABC ( TUBB4A variant)
AGS (may also have basal ganglia and WM calcification)
GM1 gangliosidosis
Demyelination Krabbe disease
Metachromatic leukodystrophy
Thin corpus callosum HSP (i.e., SPG4, SPG11, SPG15, and others)
Globus pallidus lesions T2 hypointense: NBIA (SN also involved in BPAN, MPAN), fucosidosis
T2 hyperintense: MMA, PDH deficiency, creatine deficiency syndromes
Focal atrophy or hypoplasia Glutaric aciduria type 1 (frontotemporal)
H-ABC (cerebellum ± putamen)
Joubert syndrome (cerebellum)
AGS, Aicardi-Goutières syndrome; BPAN, β-propeller protein-associated neurodegeneration; H-ABC, hypomyelination with atrophy of the basal ganglia and cerebellum; HSP, hereditary spastic paraplegia; MMA, methylmalonic aciduria; MPAN, mitochondrial membrane protein-associated neurodegeneration; NBIA, neurodegeneration with brain iron accumulation; PDH, pyruvate dehydrogenase; WM, white matter.

TABLE 38.6
Differential Diagnoses in Spastic Paraplegia
From Salinas S, Proukakis C, Crosby A, et al. Hereditary spastic paraplegia: clinical features and pathogenetic mechanisms. Lancet Neurol . 2008;7:1127–1138 (Panel, p. 1128).
Childhood Onset

  • Diplegic cerebral palsy

  • Structural (Chiari malformation, atlantoaxial subluxation)

  • Hereditary spastic paraplegia

  • Leukodystrophy (e.g., Krabbe)

  • Metabolic (arginase deficiency, abetalipoproteinemia)

  • Levodopa-responsive dystonia

  • Infection (myelitis)

  • Multiple sclerosis

Adolescent Onset

  • Cervical spine degenerative disease

  • Multiple sclerosis

  • Motor neuron disease

  • Neoplasm (primary/secondary spinal tumor, parasagittal meningioma)

  • Infection (myelitis)

  • Dural arteriovenous malformation

  • Chiari malformation

  • Adrenoleukodystrophy

  • Hereditary spastic paraplegia

  • Spinocerebellar ataxias

  • Vitamin deficiency (B 12 and E)

  • Lathyrism

  • Levodopa-responsive dystonia

  • Infection (syphilis, human T-cell leukemia virus 1, HIV)

  • Copper deficiency

Testing

The diagnostic approach to evaluating a child with hypertonia includes excluding the disorders in Tables 38.5 and 38.6 and the approach noted in Figures 38.1 and 38.2 .

Fig. 38.2, General diagnostic approach to the patient with an infantile-onset, apparently nonprogressive motor disorder. Studies are grouped by predominant clinical presentation; it may be appropriate to consider investigations from more than one group depending on the specific clinical context. CSF studies: glucose (+serum glucose), lactate, pyruvate, neurotransmitter metabolites (biogenic amines + γ-aminobutyric acid [GABA]), pterins, 5-methyltetrahydrofolate. AFP, α-fetoprotein; CP, cerebral palsy; CGH, comparative genomic hybridization; CSF, cerebrospinal fluid; GAA, α-glucosidase; HSP, hereditary spastic paraplegia; SNP, single nucleotide protein; TSH, thyroid-stimulating hormone; WES, whole-exome sequencing.

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