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Hypotonia

Definition

Hypotonia, or severely decreased muscle tone, is seen primarily in children. Low-toned muscles contract very slowly in response to a stimulus and cannot maintain a contraction for as long as a normal muscle. Hypotonia is a symptom that can be caused by many different conditions.

Description

Hypotonia, also called floppy infant syndrome or infantile hypotonia, is a condition of decreased muscle tone. The low muscle tone can be caused by a variety of conditions and is often indicative of the presence of an underlying central nervous system disorder, genetic disorder, or muscle disorder. Muscle tone is the amount of tension or resistance to movement in a muscle. It is not the same as muscle weakness, which is a reduction in the strength of a muscle, but it can co-exist with muscle weakness. Muscle tone indicates the ability of a muscle to respond to a stretch. For example, if the flexed arm of a child with normal tone is quickly straightened, the flexor muscle of the arm (biceps) will quickly contract in response. Once the stimulus is removed, the muscle then relaxes and returns to its normal resting state. A child with low muscle tone has muscles that are slow to start a muscle contraction. Muscles contract very slowly in response to a stimulus and cannot maintain a contraction for as long as a normal muscle. Because low-toned muscles do not fully contract before they again relax, they remain loose and very stretchy, never achieving their full potential of sustaining a muscle contraction over time.

Hypotonic infants, therefore, have a typical "floppy" appearance. They rest with their elbows and knees loosely extended, while infants with normal muscle tone tend to have flexed elbows and knees. Head control is usually poor or absent in the floppy infant with the head falling to the side, backward, or forward. Infants with normal tone can be lifted by placing hands under their armpits, but hypotonic infants tend to slip between the hands as their arms rise unresistingly upward. While most children tend to flex their elbows and knees when resting, hypotonic children hang their arms and legs limply by their sides. Infants with this condition often lag behind in reaching the fine and gross motor developmental milestones that enable infants to hold their heads up when placed on the stomach, balance themselves, or get into a sitting position and remain seated without falling over. Hypotonia is also characterized by problems with mobility and posture, lethargy, weak ligaments and joints, and poor reflexes. Since the muscles that support the bone joints are so soft, there is a tendency for hip, jaw, and neck dislocations to occur. Some hypotonic children also have trouble feeding and are unable to suck or chew for long periods. Others may also have problems with speech or exhibit shallow breathing. Hypotonia does not, however, affect intellect.

Demographics

No demographic information as of 2004 was available for hypotonia, since it is a symptom of an underlying disorder. However, a study conducted in year 2000 by the University of Illinois provides some insights. The study followed 243 infants with hypotonia for three to seven years. By the age of three, about 30 percent had minimal problems and 46 percent had significant impairments, while 24 percent of the infants were normal. Hypotonic infants who matured into children with minimal disabilities were highly likely to have poor motor coordination at age three (78%). About 25 percent had learning problems or language delay ; 20 percent had borderline cognition or attention deficits; and 66 percent had two or more of these characteristics.

Causes and symptoms

Hypotonias are often of unknown origin. Scientists believe that they may be caused by trauma; environmental factors; or by other genetic, muscle, or central nervous system disorders. The National Institutes of Health list the following common causes of hypotonia:

The following are common symptoms associated with hypotonia. Each child may experience different symptoms, depending on the underlying cause of the hypotonia:

Normally developing children tend to develop motor skills, posture control, and movement skills by a given age. Motor skills are divided into two categories. Gross motor skills include the ability of an infant to lift its head while lying on the stomach, to roll over from its back to its stomach. Normally, by a given age, a child develops the gross motor skills required to get into a sitting position and remain seated without falling over, crawl, walk, run, and jump. Fine motor skills include the ability to grasp, transfer an object from one hand to another, point out an object, follow a toy or a person with the eyes, or to feed oneself. Hypotonic children are slow to develop these skills, and parents should contact their pediatrician if they notice such delays or if their child appears to lack muscle control, especially if the child previously seemed to have normal muscle control.

Diagnosis

Hypotonia is normally discovered within the first few months of life. Since it is associated with many different underlying disorders, the doctor will accordingly seek to establish a family history as well as the child's medical history. A physical examination will be performed, usually including a detailed nervous system and muscle function examination. The latter may be performed with instruments, such as lights and reflex hammers, and usually does not cause any pain to the child. Most of the disorders associated with hypotonia also cause other symptoms that, when taken together, suggest a specific disorder and cause for the hypotonia. Specific diagnostic tests used will vary depending on the suspected cause of the hypotonia. Typical medical history questions include:

The following diagnostic tests may also be used:

Treatment

When hypotonia is caused by an underlying condition, that condition is treated first, followed by symptomatic and supportive therapy for the hypotonia. Physical therapy can improve fine motor control and overall body strength. Occupational and speech-language therapy can help breathing, speech, and swallowing difficulties. Therapy for infants and young children may also include sensory stimulation programs. Specific treatment for hypotonia is determined by the child's physician based on the following:

No specific treatment is required to treat mild congenital hypotonia, but children with this problem may periodically need treatment for common conditions associated with hypotonia, such as recurrent joint dislocations. Treatment programs to help increase muscle strength and sensory stimulation programs are developed once the cause of the child's hypotonia is established. Such programs usually involve physical therapy through an early intervention or school-based program among other forms of therapy.

Hypotonic children are often treated by one or more of the following specialists:

In some hypotonic infants, sucking is weak and in some cases not present at all. They do not act hungry or show interest in feeding. Special techniques and procedures are then required to provide adequate nutrition , such as special nipples, manipulation of mouth and jaw, and on rare occasions, insertion of a gastrostomy tube.

Prognosis

The outcome in any particular case depends largely on the nature of the underlying disease. Hypotonia can be life long, but in some cases, muscle tone improves over time. Children with mild hypotonia may not experience developmental delay , although some children acquire gross motor skills (sitting, walking, running, jumping) more slowly than most. Most hypotonic children eventually improve with therapy and time. By age five, they may not be the fastest child on the playground, but many will be there with their peers and will be holding their own. Some children are more severely affected, requiring walkers and wheelchairs and other adaptive and assistive equipment.

Prevention

As of 2004 there was no prevention for hypotonia. However, measures of prevention are increasingly possible in the early 2000s for several underlying disorders.

Parental concerns

Parents of an hypotonic child must follow the treating physician's orders for treatment of the underlying cause. They must exercise special care when lifting and carrying the hypotonic infant to avoid causing an injury to the child. If lifted under the armpits, the hypotonic infant's arms will raise with no resistance and easily slip between the hands.

A six-week-old baby girl is held horizontally by the trunk in a test for hypotonia, sometimes called floppy infant syndrome. The girl is normal. (Saturn Stills/Science Photo Library/Photo Researchers, Inc.)
A six-week-old baby girl is held horizontally by the trunk in a test for hypotonia, sometimes called "floppy infant syndrome." The girl is normal.
(Saturn Stills/Science Photo Library/Photo Researchers, Inc.)

Another source of concern that parents face is addressing the special needs of their hypotonic child. The world of typical children can be a difficult place for a hypotonic child, and it is tempting to isolate the child. It is not easy to go to a playgroup of toddlers when a child's latest milestone is getting from the floor into a sitting position while the other children are running across the room. There are resources for parents to help their child become as able and independent as he or she can possibly be, and the family physician is a good resource for advice.

See also Bayley Scales of Infant Development ; Muscular dystrophy .

Resources

Amiel-Tison, Claudine, et al. Neurological Development from Birth to Six Years: Guide for Examination and Evaluation. Baltimore, MD: Johns Hopkins University Press, 2001.

Preedy, Victor R., and Timothy J. Peters. Skeletal Muscle: Pathology, Diagnosis, and Management of Disease , 3rd ed. Edited by Kenneth J. Ryan. Albuquerque, NM: Health Press, 2002.

KEY TERMS

Ataxia —A condition marked by impaired muscular coordination, most frequently resulting from disorders in the brain or spinal cord.

Biceps —The muscle in the front of the upper arm.

Biopsy —The surgical removal and microscopic examination of living tissue for diagnostic purposes or to follow the course of a disease. Most commonly the term refers to the collection and analysis of tissue from a suspected tumor to establish malignancy.

Central nervous system —Part of the nervous system consisting of the brain, cranial nerves, and spinal cord. The brain is the center of higher processes, such as thought and emotion and is responsible for the coordination and control of bodily activities and the interpretation of information from the senses. The cranial nerves and spinal cord link the brain to the peripheral nervous system, that is the nerves present in the rest of body.

Chromosome —A microscopic thread-like structure found within each cell of the human body and consisting of a complex of proteins and DNA. Humans have 46 chromosomes arranged into 23 pairs. Chromosomes contain the genetic information necessary to direct the development and functioning of all cells and systems in the body. They pass on hereditary traits from parents to child (like eye color) and determine whether the child will be male or female.

Computed tomography (CT) —An imaging technique in which cross-sectional x rays of the body are compiled to create a three-dimensional image of the body's internal structures; also called computed axial tomography.

Fine motor skill —The abilities required to control the smaller muscles of the body for writing, playing an instrument, artistic expression and craft work. The muscles required to perform fine motor skills are generally found in the hands, feet and head.

Flexor muscle —A muscle that serves to flex or bend a part of the body.

Gene —A building block of inheritance, which contains the instructions for the production of a particular protein, and is made up of a molecular sequence found on a section of DNA. Each gene is found on a precise location on a chromosome.

Genetic disease —A disease that is (partly or completely) the result of the abnormal function or expression of a gene; a disease caused by the inheritance and expression of a genetic mutation.

Gross motor skills —The abilities required to control the large muscles of the body for walking, running, sitting, crawling, and other activities. The muscles required to perform gross motor skills are generally found in the arms, legs, back, abdomen and torso.

Immune response —A physiological response of the body controlled by the immune system that involves the production of antibodies to fight off specific foreign substances or agents (antigens).

Immune system —The system of specialized organs, lymph nodes, and blood cells throughout the body that work together to defend the body against foreign invaders (bacteria, viruses, fungi, etc.).

Magnetic resonance imaging (MRI) —An imaging technique that uses a large circular magnet and radio waves to generate signals from atoms in the body. These signals are used to construct detailed images of internal body structures and organs, including the brain.

Motor control —The control of movement and posture.

Motor neuron —A nerve cell that specifically controls and stimulates voluntary muscles.

Muscle tone —Also termed tonus; the normal state of balanced tension in the tissues of the body, especially the muscles.

Muscle weakness —Reduction in the strength of one or more muscles.

Neurons —Any of the conducting cells of the nervous system that transmit signals.

Recessive disorder —Disorder that requires two copies of the predisposing gene one from each parent for the child to have the disease.

Spinal cord —The elongated nerve bundles that lie in the spinal canal and from which the spinal nerves emerge.

Underlying condition —Disorder or disease that causes the appearance of another medical disorder or condition.

Child Development Institute (CDI). 3528 E. Ridgeway Road, Orange, California 92867. Web site: http://www.childdevelopmentinfo.com.

Genetic and Rare Diseases Information Center. PO Box 8126, Gaithersburg, MD 20898–8126. Web site: http://www.rarediseasesinfo.nih.gov.

March of Dimes Birth Defects Foundation. PO Box 3006, Rockville, MD 20847. Web site: http://www.marchofdimes.com.

Muscular Dystrophy Association. 3300 East Sunrise Drive, Tucson, AZ 85718–3208. Web site: http://www.mdausa.org.

National Institute of Child Health and Human Development (NICHD). 31 Center Drive, Rm. 2A32, MSC 2425, Bethesda, MD 20892–2425. Web site: http://www.nichd.nih.gov.

National Institute of Neurological Disorders and Stroke (NINDS). PO Box 5801, Bethesda, MD 20824. Web site: http://www.ninds.nih.gov.

National Organization for Rare Disorders (NORD). PO Box 1968, 55 Kenosia Avenue, Danbury, CT 06813–1968. Web site: http://www.rarediseases.org.

"Hypotonia." Family Village. Available online at http://www.familyvillage.wisc.edu/lib_hypot.htm (accessed October 18, 2004).

"What is Benign Congenital Hypotonia?" Benign Congenital Hypotonia Site. Available online at http://www.lightlink.com/vulcan/benign/aboutbch.htm (accessed October 18, 2004).

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