Course:KIN366/ConceptLibrary/Hypotonia

Movement Experiences for Children
KIN 366
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Instructor:	Dr. Shannon S.D. Bredin
Email:	shannon.bredin@ubc.ca
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Hypotonia is a general term used to describe the physical condition of reduced muscle tone in both children and adults (Martin et al., 2005). A strong correlation exists between children with congenital hypotonia and parents with a positive history of joint hyperlaxity (Carboni et al., 2002). It is symptomatic of abnormalities of the central nervous system, any element of the motoneuron, or both, which results in diminished skeletal muscle tone (Lisi & Cohn, 2011). The two types of hypotonia are respectively labeled as central, and peripheral hypotonia. The underlying cause of hypotonia is difficult to exactly determine because it presents itself as a feature of many related disorders and chromosomal abnormalities (Lisi & Cohn, 2011). Many disorders of the peripheral nervous system can be sourced to the specific components of the motor unit. The evaluation of a hyptonic individual is therefore a process of determining where the lesion in the motor unit is located to conclude the diagnosis (Miller et al., 1993).

Central Hypotonia

Central hypotonia results from disorders which primarily affect the central nervous system. This includes the spinal cord (Richer et al., 2001). Abnormalities occurring in the central nervous system may interrupt pathways involved in creating muscle tone, thus decreasing its function (Richer et al., 2001). Clinical findings have suggested that anomalies of the central nervous system may include hyperreflexia, cognitive developmental delay, and seizures (Lisi & Cohn, 2011). The most common chromosomal cause of central hypotonia is Down syndrome (Martin et al., 2005).

Peripheral Hypotonia

Peripheral hypotonia is primarily caused by abnormalities of the motor unit, peripheral nerve, neuromuscular junction, or muscle (Richer et al., 2001). Symptoms of disorders originating in the neuromuscular region may include muscular weakness, lack of antigravity movements, muscular atrophy, fasiculations, and/or diminished reflexes (Lisi & Cohn, 2011). Cognitive function, however, remains largely unimpaired although gross and fine motor skills may show some delay in development depending on the severity of muscular weakness (Lisi & Cohn, 2011).

Characteristics of Hypotonia

Posture

Hypotonic children have a rounded shoulder posture, and tend to use external supports to lean against, which could potentially be viewed as a compensatory strategy for the decreased postural control or decreased strength they experience with the disorder (Martin et al., 2005).

Flexibility

Children with hypotonia show characteristics of increased flexibility and hypermobile joints. These characteristics, however, should not be confused with increased extensibility of the muscles themselves. (Martin et al., 2005)

Medical Diagnosis

The most commonly identified medical diagnoses associated with hypotonia are Down syndrome, cerebral palsy, developmental delay, autism, and other genetic syndromes (Martin et al., 2005).

Neonatal Hypotonia

Peripheral hypotonia in infants doesn't affect alertness, response to surroundings, or sleep-waking cycles, whereas central hypotonia presents itself in infants as inability to track visually, failure to imitate facial gestures, and appearance of lethargy (Miller et al., 1993). Other characteristics suggestive of cerebral involvement include the presence of dysmorphic features, and abnormalities of the organ systems, such as heart defects and limb malformations (Miller et al., 1993).

While awake, the hypotonic infant may show deficiencies in movement. When supine, they may assume a “frog-leg” posture with their hips open, knees pointing outward, and toes pointing inward (Miller et al., 1993). When lying prone, they often assume a “rump’s up” position with their knees bent under the abdomen and buttocks in the air (Miller et al., 1993). When testing ventral suspension, the baby is held upright under the arms; hypotonic infants tend to slide down through the examiner’s grip, unable to keep their shoulder joints locked to prevent slipping (Miller et al., 1993). In horizontal suspension, the infant is held slightly above a surface in prone position with the examiner’s hands supporting the infant’s chest and abdomen. Neonates with normal muscle tone development will be able to hold their backs straight with their head and legs remaining even with their body, while hypotonic infants are unable to support their head and legs, draping themselves over the examiner’s hand (Miller et al., 1993). This characteristic is often denoted as “floppy baby syndrome”. As the infant develops, physiotherapy should be implemented as a treatment until the patient can walk unsupported (Carboni et al., 2002).

Characteristics of Hypotonia in Children

Sitting

In a study done on hypotonic children, almost all patients observed assumed the “W” position of the lower limbs when sitting on the floor with their bottom on their heels, maintaining the foot in plantar flexion (Carboni et al., 2002).

Standing

Shoulders tended to remain in adduction while standing, with the scapulae winged out. Accentuation of the spinal curvature was observed, particularly hyperlordosis, and protrusion of the abdominal area; all signs of non-fixed scoliosis of the spine. Under load, feet were flat and valgus. When the feet were not weight bearing, there was enhancement of the plantar arch (Carboni et al., 2002).

Gait

The children with hypotonia tend to lack heel-toe progession in walking. They will often walk on their toes to avoid stumbling, and also lift their knees up excessively when taking steps, maintaining their foot in plantar flexion. Most hypotonic children cannot walk on their heels (Carboni et al., 2002).

Overall, the hypotonic muscles continually work in a shortened condition, perpetuating the diminished condition they are in.

Treatment Options for Children with Hypotonia

For central hypotonia, treatment largely revolves around supportive and symptomatic therapy (Martin et al., 2005). Proven to be the most beneficial modes of improving central hypotonia, physical, occupational, and speech therapy are relatively effective treatment strategies (Martin et al., 2005). Additionally, although understudied in children with central hypotonia, aquatic therapy and hippotherapy are viable treatment options as well, as they have been shown to increase function and endurance in some children with physical disabilities (Martin et al., 2005). Playing sports is recommended for hypotonic children as they may learn to adjust their gait and posture for better sport performance (Carboni et al., 2002).

How Does Hypotonia Affect Childhood Movement Experiences?

Due to the weaknesses and limitations in muscle tonicity, hypotonia primarily affects fine and gross motor abilities. In children, this results in delayed fundamental motor skills (Easter, 2005). As the hypotonic child develops, motor skills will continue to improve, but will not develop as quickly as other skills, such as language and social skills (Easter, 2005). It is also possible that motor development may taper off due to hypotonia and other products of central nervous system disorders such as brain damage from seizures, low cognitive level, or adverse effects of medication(s) (Easter, 2005).

Strategies and Recommendations to Enhance Movement Experiences for Children with Hypotonia

At their maximum length, muscle fibers produce 19% more sarcomeres than at resting length, while in the shortened position, muscle fibers lose approximately 40% of the sarcomeres compared to resting length (Carboni et al., 2002). In hypotonic individuals, increased joint mobility is believed to be a main cause of muscle shortening, keeping the muscles shortened in both the passive and active states for extended periods of time (Carboni et al., 2002). Even if weak since birth, hypotonic muscles have been observed to progressively become weaker because of insufficient use (Carboni et al., 2002). Until 8 years of age, muscle shortening seems to be reversible with stretching exercises and physiotherapy. After this age, the condition seems to become slowly irreversible (Carboni et al., 2002). The triceps surae and flexor hallucis longus seem to be particularly susceptible to irreversible muscle shortening at the lower end of the age threshold, while the abdominal, tibialis anterior, and peroneus muscles weaken later as a result of reduced use as antagonist muscles (Carboni et al., 2002). As mentioned above, stretching exercises and physiotherapy targeting these muscles could counteract shortening, preserve the strength of the muscle, and prevent further deficits (Carboni et al., 2002). Continuous exercise should also be practiced as an active treatment to reduce muscular deficits, including playing sports. In a study done on hypotonic individuals, all patients that regularly participated in sporting activities did not develop any kind of muscle shortening (Carboni et al., 2002). Active stretching exercises and muscle strengthening activities are crucial to avoiding muscular shortening in hypotonic children.

Common Genetic Conditions Associated with Hypotonia

Prader-Willi Syndrome

Associated with central hypotonia, prominent features include: “global development delay, short stature, genital hypoplasia, and failure to thrive in infancy leading to hyperphasia at approximately one year of age.” (Lisi & Cohn, 2011)

Williams Syndrome

Similar to gene deletion, Williams syndrome is relatively common syndrome associated with central hypotonia (Lisi & Cohn, 2011).

Creatine Deficiency Syndrome

A frequent manifestation of peripheral hypotonia, creatine deficiency disorders occur when there are errors of creatine synthesis and transport. A common symptom of these disorders include intellectual disability, speech delay, and epilepsy, as well as failure to thrive, growth retardation, and movement disorders (Stöckler-Ipsiroglu et al., 2012)

Spinal Muscular Atrophy (SMA)

Characterized by progressive muscle weakness, SMA is an autosomal recessive condition caused by the degeneration and loss of lower motoneurons in both the spinal cord and the brainstem (Lisi & Cohn, 2011)

Pompe Disease

An inherited disorder, Pompe disease is characterized by the buildup of glycogen in cells, leading to muscle and organ damage, and death (King et al., 2002).

Barth Syndrome

Barth syndrome is an X-chromosome linked recessive disorder that typically shows symptoms of cardiomyopathy, skeletal myopathy, growth retardation, neutropenia, and increased urinary levels of 3-methylflutaconic acid (Jefferies, 2013)

And many more

Summary

The diagnostic profile of neonates showing characteristics of hyptonia is extremely diverse and can be attributed to a wide variety of causes (Richer et al., 2001). A thoughtful and thorough approach must be taken for the diagnosis and management of hypotonia, as it often presents with several other underlying manifestations. Symptomatic treatment can and needs to be tailored toward the individual to promote maximum ability to thrive.

References

Carboni, P., Pisani, F., Crescenzi, A., & Villani, C. (2002). Congenital hypotonia with favorable outcome.Pediatric Neurology, 26(5), 383-386.
Easter, S. (2005). A LONGITUDINAL STUDY OF THE SPEECH, LANGUAGE, MOTOR, AND SOCIAL DEVELOPMENT IN A HYPOTONIC CHILD.
Jefferies, J. (2013). Barth syndrome. American Journal of Medical Genetics Part C: Seminars in Medical Genetics, 163(3), 198-205.
King, R., Stansfield, W., & Mulligan, P. (2002). A dictionary of genetics (6th ed.). New York: Oxford University Press.
Lisi, E., & Cohn, R. (2011). Genetic evaluation of the pediatric patient with hypotonia: Perspective from a hypotonia specialty clinic and r eview of theliterature. Developmental Medicine and Child Neurology. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8749.2011.03918.x/epdf
Martin, K., Inman, J., Kirschner, A., Deming, K., Gumbel, R., & Voelker, L. (2005). Characteristics of Hypotonia in Children: A Consensus Opinion of Pediatric Occupational and Physical Therapists. Pediatric Physical Therapy, 17(4), 275-282.
Miller, V., Delgado, M., & Iannaccone, S. (1993). Neonatal Hypotonia. Seminars in Neurology, 13(1), 73-83.
Richer, L., Shevell, M., & Miller, S. (2001). Diagnostic profile of neonatal hypotonia: An 11-year study.Pediatric Neurology, 25(1), 32-37.
Stöckler-Ipsiroglu, S., Mercimek-Mahmutoglu, S., & Salomons, G. (2012). Creatine Deficiency Syndromes. In Inborn Metabolic Diseases: Diagnosis and Treatment (5th ed., pp. 239-247). Springer Berlin Heidelberg.