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.