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. Infants with hypotonia have a floppy quality or “rag doll” appearance because their arms and legs hang by their sides and they have little or no head control. Other symptoms of hypotonia include problems with mobility and posture, breathing and speech difficulties, lethargy, ligament and joint laxity, and poor reflexes. Hypotonia does not affect intellect. However, depending on the underlying condition, some children with hypotonia may take longer to develop social, language, and reasoning skills. When hypotonia develops in the adult years, it may be due to diseases associated with cerebellar degeneration (such as multiple sclerosis, Friedreich’s ataxia, or multiple system atrophy) in which neurons in the cerebellum -- the area of the brain that controls muscle coordination and balance -- deteriorate and die.

Treatment begins with a thorough diagnostic evaluation, including an assessment of motor and sensory skills, balance and coordination, mental status, reflexes, and functioning of the nerves. Diagnostic tests such as a CT scan of the brain, an EMG to evaluate nerve and muscle function, or an EEG to measure electrical activity in the brain may also be necessary. Once a diagnosis has been made, the underlying 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.

Hypotonia can be a life-long condition. In some cases, however, muscle tone improves over time.

Prepared by the National Institutes of Health