Hypotonia Health Article

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:

• Down syndrome: a chromosome abnormality, usually due to an extra copy of the twenty-first chromosome.
• Myasthenia gravis: a neuromuscular disorder characterized by variable weakness of voluntary muscles, which often improves with rest and worsens with activity. The condition is caused by an abnormal immune response.
• Prader-Willi syndrome: a congenital disease characterized by obesity, severe hypotonia, and decreased mental capacity
• Kernicterus: also called Rh incompatibility, a condition that develops when there is a difference in Rh blood type between that of the mother (Rh negative) and that of the fetus (Rh positive).
• Cerebellar ataxia: a movement disorder which with its sudden onset, often following an infectious viral disease, causes hypotonia.
• Infant botulism: a type of botulism, in which Clostridium botulinum bacteria grow within an infant's digestive tract, producing a toxin which is potentially life-threatening.
• Familial dysautonomia: also called Riley-Day syndrome, an inherited disorder that affects the function of nerves throughout the body.
• Marfan syndrome: an inherited disorder of connective tissue (tissue that adds strength to the body's structures), affecting the skeletal system, cardiovascular system, eyes, and skin.
• Muscular dystrophy: a group of disorders characterized by progressive muscle weakness and loss of muscle tissue.
• Achondroplasia: a disorder of bone growth that causes the most common type of dwarfism.
• Trisomy 13: a syndrome associated with the presence of a third number 13 chromosome.
• Sepsis: a severe, life-threatening illness caused by overwhelming infection of the bloodstream by toxin-producing bacteria.
• Aicardi syndrome: a rare genetic disorder characterized by infantile spasms (jerking), absence of the corpus callosum (the connection between the two hemispheres of the brain), mental retardation, and lesions of the retina of the eye or optic nerve.
• Canavan disease: an inherited metabolic disorder characterized by degeneration of the white matter of the brain.
• Congenital hypothyroidism: a disorder that results from decreased thyroid hormone production.
• Hypervitaminosis D: a condition that appears several months after excessive doses of vitamin D are administered.
• Krabbe disease: an inherited disorder characterized by a deficiency of the enzyme galactosylcereamidase, resulting in destruction of myelin, the fatty material that surrounds and insulates many of the nerves.
• Metachromatic leukodystrophy: an inherited disease characterized by the absence of the enzyme arylsulfatase A, which causes a material called cerebroside sulfate to accumulate in cells, which is toxic to cells, especially to the cells of the nervous system.
• Methylmalonic academia: an inherited metabolic disorder, usually diagnosed in infancy, which causes the accumulation of methylmalonic acid in the body and can lead to severe metabolic disturbances.
• Rickets: a childhood disorder involving softening and weakening of the bones, primarily caused by lack of vitamin D, calcium, or phosphate.
• Spinal muscular atrophy type 1 (Werdnig-Hoffman): a group of inherited diseases causing progressive muscle degeneration and weakness, eventually leading to death.
• Tay-Sachs disease: a genetic disorder found predominantly in Ashkenazi Jewish families results in early death.
• Vaccine reaction: any injury or condition that occurs as a result of a vaccination.

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

• decreased muscle tone; muscles feel soft and doughy
• ability to extend limb beyond its normal limit
• failure to acquire motor skill developmental milestones (such as holding head up without support from parent, rolling over, sitting up without support, walking)
• feeding problems (inability to suck or chew for prolonged periods)
• shallow breathing
• mouth hangs open with tongue protruding (underactive gag reflex)