Many disorders can cause poor muscle tone, or hypotonia, in a newborn. Hypotonia may be a temporary condition related to birth trauma or prematurity or the result of a congenital abnormality such as Down syndrome. Hypotonia in a newborn requires medical evaluation to determine the cause and plan treatment. Central hypotonia, the more common type, according to Aukland Health Services, is caused by damage to the brain, while peripheral hypotonia may come from injuries to one specific area of the body.
Prematurity is the most common single cause of hypotonia, due to the immaturity of the central nervous system. Preemies often assume a "frog-legged" position, with legs flopping out to the side. Hypotonia related to prematurity improves as the central nervous system matures, unless other factors, such as cerebral palsy, also cause hypotonia. Infection or other illness, such as respiratory distress, can also cause temporary hypotonia in newborns. Maternal drugs such as magnesium sulfate given to decrease the risk of seizures, pain medications and spinal anesthesia can also cause temporary hypotonia. Temporary myasthenia gravis occurs in 12 percent of infants whose mothers have the disorder, Dr. Alan Hill reports in the 2005 edition of "Current Management in Child Neurology."
Congenital disorders such as Down syndrome, Prader-Willi syndrome, familial muscle disorders or metabolic disorders and other chromosomal abnormalities can cause floppiness in a newborn. Down syndrome is the most common congenital disorder associated with hypotonia, according to Hill. In these cases, poor muscle tone is permanent, although physical therapy can help the child improve muscle strength. In some cases, muscle may weaken further as the child gets older.
Birth trauma can cause cerebral palsy or injuries to nerves or spine that can cause low muscle tone. Cerebral palsy affects the brain; bleeding in the brain or lack of oxygen at the time of birth can cause cerebral palsy. A baby with cerebral palsy may have either low muscle tone or stiff muscles, depending on the area of brain injury. In most cases, acquired conditions neither worsen or improve over time. Congenital infections such as toxoplasmosis, rubella, cytomegalovirus or herpes can also cause poor muscle tone.
The first step to treating poor muscle tone in a newborn is to determine its cause. Early intervention and therapy may improve poor muscle tone in many cases of hypotonia. While your child may continue to have poor muscle tone compared to others of the same age, physical and occupational therapy can maximize his potential.