Hypotonia is a condition of abnormally low muscle tone (the amount of tension or resistance to movement in a muscle), often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength. Recognizing hypotonia, even in early infancy, is usually relatively straightforward, but diagnosing the underlying cause can be difficult and often unsuccessful.

Hypotonia is a medical term used to describe decreased muscle tone (the amount of resistance to movement in a muscle). It is not the same as muscle weakness, although the two conditions can co-exist. Hypotonia may be caused by trauma, environmental factors, or by genetic, muscle, or central nervous system disorders, such as Down syndrome, muscular dystrophy, cerebral palsy, Prader-Willi syndrome, myotonic dystrophy, and Tay-Sachs disease. Sometimes it may not be possible to find what causes hypotonia.

An infant with hypotonia exhibits a floppy quality or "rag doll" feeling when he or she is held. Infants with this problem lag behind in acquiring certain fine and gross motor developmental milestones that enable a baby to hold his or her head up when placed on the stomach, balance themselves or get into a sitting position and remain seated without falling over.

Symptoms of Hypotonia

The most common symptoms of hypotonia involve problems with mobility and posture, breathing and speech difficulties, lethargy, ligament and joint laxity, and poor reflexes.

Infants who are hypotonic will let their elbows and knees hang loosely instead of flexed as normal. The infant may have poor or no head control.

The extent and occurrence of specific objective manifestations depends upon the age of the patient, the severity of the hypotonia, the specific muscles affected, and sometimes the underlying cause. For instance, some hypotonics may experience constipation, while others have no bowel problems.

Twitching may occur in the tongue and in affected limbs. The patient may experience muscle pain and muscle cramps. Some patients experience more difficulty swallowing saliva and liquids than solid food.

Since hypotonia is most often diagnosed during infancy, it is also known as "floppy infant syndrome" or "infantile hypotonia." Infants who suffer from hypotonia are often described as feeling and appearing as though they are "rag dolls" or a "sack of jello," easily slipping through one's hands.

Causes of Hypotonia

Hypotonia may be caused by trauma, environmental factors, or by genetic, muscle, or central nervous system disorders.

Down syndrome occurs when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21. The extra chromosome causes problems with the way the body and brain develop.

Hypotonia can be caused by a variety of conditions including those that involve the central nervous system, muscle disorders and genetic disorders. Some common causes can include but are not limited to Down syndrome, Muscular dystrophy, Cerebral palsy, Prader-Willi Syndrome, Myotonic dystrophy, Marfan syndrome and Tay-Sachs disease.

A number of different genetic disorders are associated with hypotonia, and may affect the nerves (and by extension the muscles), or the muscles only. Most genetic conditions are generalized (affecting multiple muscle groups) and progressive. Some genetic conditions are hereditary.

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.