What Is Hypotonia?

Hypotonia is decreased muscle tone. It is often an early sign of a chronic condition such as a neuromuscular disorder, genetic disease, or metabolic disease.

Hypotonia is different from muscle weakness. Normal muscles always have a small amount of contraction, even when they are relaxed. People with hypotonia do not have any contractions in their muscles. 

This condition can affect children and adults and is often detected during infancy. Babies with hypotonia appear floppy and have limbs that look like a rag doll. They usually have poor head control.

This article will describe the signs and causes of hypotonia, possible diagnostic tests, and treatment options. 

Symptoms

Hypotonia describes an absence of muscle tone. Common signs and symptoms include:

• Decreased muscle tone: The muscles feel soft and doughy. 
• Extended limbs: Most infants rest with their elbows and knees flexed. Those with hypotonia rest with their joints and limbs extended.
• Delayed milestones: Infants with hypotonia do not meet developmental milestones. They cannot hold their heads up, roll over, sit up, or learn to walk at the expected age. 
• Feeding problems: Individuals with hypotonia cannot suck or chew for long periods of time. This leads to issues with feeding and taking in enough calories each day.
• Speech delays: Infants and children with hypotonia have trouble learning to speak and express themselves. 
• Breathing difficulties: Because the muscles in the chest lack tone, they cannot assist with breathing. People with hypotonia usually exhibit shallow breathing. 
• Protruding tongue: The mouth usually hangs open, and the tongue protrudes out.
• Joint dislocations: Hip, jaw, and neck dislocations are common in those with hypotonia.

Causes

There are several possible causes of hypotonia in babies, children, and adults. Muscle tone is controlled by the signals that run from the brain to the nerves in the muscles. When one of these components is damaged, hypotonia results.

Damage to the brain, spinal cord, nerves, or muscles could result in hypotonia. Damage to these structures could come from trauma, genetics, infection, or an underlying medical condition. 

Common causes of hypotonia include:

• Down syndrome (also called trisomy 21, a common chromosomal disorder)
• Muscular dystrophy (nine inherited disorders that involve muscle weakness)
• Cerebral palsy (a motor disability that affects the brain and muscles)
• Prader-Willi syndrome (a genetic disorder marked by poor feeding during infancy)
• Myotonic dystrophy (type of muscular dystrophy characterized by progressive muscle wasting and weakness, impacting skeletal muscles and internal organs)
• Tay-Sachs disease (a rare, usually fatal, genetic disorder that results in the destruction of nerve cells in the brain and spinal cord)

Diagnosis

Hypotonia is usually discovered during infancy because of delayed motor skills. Infants with hypotonia are not able to meet fine or gross motor milestones because they lack muscle strength and control to achieve them. 

When you and your healthcare provider discover your child’s hypotonia, the next step is to determine the underlying cause. This usually includes a visit to a pediatric neurologist. A pediatric geneticist may be consulted as well. 

The diagnostic process starts with a physical exam to evaluate the nervous system and muscle function. Depending on your child’s symptoms, one or more of the following tests may be recommended:

• Computed tomography (CT) scan: Uses X-rays to produce three-dimensional images of organs and bodily structures
• Magnetic resonance imaging (MRI): Uses a magnetic field and computer-generated radio waves to create detailed images of structures inside the body
• Electromyography (EMG) and nerve conduction study (NCS): Evaluates how well the muscles and nerves are functioning
• Electroencephalogram (EEG): Records electrical activity in the brain 

Treatment 

Treatment for hypotonia depends on the underlying cause. Once the diagnosis is made, the treatment plan is developed based on the underlying condition or injury. Once the cause itself is addressed, the healthcare provider will help the patient manage their symptoms. 

Two forms of treatment that are very helpful for hypotonia are physical therapy and occupational therapy. A physical therapist can assist with muscle stretching and strengthening over time. An occupational therapist specializes in fine motor skills and can provide education and training in speech and swallowing techniques. 

Prognosis

The prognosis for hypotonia depends on the underlying cause. Many of the neuromuscular and genetic diseases that cause hypotonia cannot be cured. However, many of the symptoms can be addressed. 

It’s important to note that hypotonia is often a sign of a serious medical condition and should be evaluated by a healthcare provider as soon as possible. 

Summary

"Hypotonia" means "lack of muscle tone." It is usually a sign of an underlying medical disorder such as a neuromuscular, genetic, or metabolic disease. Common symptoms of hypotonia include decreased muscle tone, extended limbs, delayed milestones, feeding problems, speech delays, breathing difficulties, and more.

Possible causes include Down syndrome, muscular dystrophy, cerebral palsy, and Prader-Willi syndrome. Treatment for hypotonia depends on the underlying cause. Once the cause is addressed, the healthcare team will then address the symptoms. Your care team will likely include a physical therapist and occupational therapist.

A Word From Verywell

Hypotonia is a concerning sign that often means there is a serious medical condition causing it. Discovering that your infant has hypotonia is devastating for parents, and the diagnostic process can be long and overwhelming. Stay in close contact with your healthcare provider and reach out for help as often as you can.