Hypotonia is a medical term that describes decreased muscle tone.
Healthy muscles are never fully relaxed. They retain a certain amount of tension and stiffness (muscle tone) that can be felt as resistance to movement.
For example, a person relies on the muscle tone in their back and neck to maintain their posture when standing or sitting up. Muscle tone decreases during sleep, so if you fall asleep sitting up you may find that you wake up with your head flopped forward.
Hypotonia is not the same as muscle weakness, although it can still be difficult to use the affected muscles. Depending on the cause, weakness may sometimes develop in association with hypotonia.
Newborn and young children with severe hypotonia are often described as being "floppy" or like a "rag doll". However, as muscle tone develops during pregnancy, premature newborn babies may have decreased muscle tone simply as a result of being premature.
Causes of hypotonia
Hypotonia is a symptom that can be a feature of various underlying health conditions, many of which are inherited (passed on from one family member to another).
It can also occur in cases of cerebral palsy, where a number of neurological (brain-related) problems affect a child's co-ordination and movement, and after serious infections such as meningitis (an infection of the outside membrane of the brain).
Read more about the causes of hypotonia.
If hypotonia is suspected, your child will be referred to a specialist paediatrician or neurologist. They will ask you questions about your family history, your pregnancy, delivery any problems that have occurred since birth.
As some conditions that cause hypotonia involve problems with other organs, your child will have some blood tests.
Other tests may also help to diagnose the underlying condition that is causing hypotonia. These could include detailed scans such as a computerised tomography (CT) scan or a magnetic resonance imaging (MRI) scan.
Read more about how hypotonia is diagnosed.
The recommended treatment plan for hypotonia will depend on the underlying cause. Hypotonia is therefore very variable: sometimes improving, sometimes staying the same and sometimes worsening over time.
A baby born prematurely may have hypotonia but it will usually improve as they get older. Babies with hypotonia that is caused by an infection or another condition will usually be cured of it if the condition is successfully treated.
It's often not possible to cure the underlying cause of hypotonia. Where hypotonia is inherited, it will persist throughout a person’s life, but with treatment their ability to function can often be improved. This can involve using physiotherapy, occupational therapy and speech and language therapy.
Someone with hypotonia can also be taught to develop coping strategies, although ongoing support and care may also be needed.
Read more about treating hypotonia.
Hypotonia (decreased muscle tone) is not a condition in itself but a symptom of an underlying condition.
How to recognise hypotonia
Hypotonia that is present at birth usually becomes noticeable by the time a child is six months old. Signs include:
- They have little or no control of their neck muscles so their head tends to flop.
- They feel limp when you hold them, as though they could easily slip through your hands.
- They are unable to place any weight on their leg or shoulder muscles.
- Their arms and legs hang straight down from their sides, rather than bending at their elbows, hips and knees.
- They may find sucking and swallowing difficult and they may have a weak cry.
A child with hypotonia may take longer to reach developmental milestones, such as:
- sitting up
- feeding themselves
An adult with hypotonia may have the following problems:
- becoming clumsy
- falling frequently
- difficulty with getting up from a lying or sitting position
- an unusually high degree of flexibility in the hips, elbows and knees
- difficulty reaching for or lifting an object
To function normally, muscles depend on signals from nerves called motor nerves.
There are two types of hypotonia (decreased muscle tone) that can occur due to problems related to the motor nerves. These are described below.
- Central hypotonia: decreased muscle tone that occurs due to disrupted nerve signals in the brain or spinal cord.
- Peripheral hypotonia: decreased muscle tone that can occur as a result of nerve damage between the spinal cord and muscle, or due to disruption in the communication between the end of the nerve and the surface of the muscle, or abnormalities in the muscles themselves.
Nerves are covered by a substance called myelin. Myelin insulates the nerve fibres and helps carry messages to and from your brain quickly and smoothly. If myelin is damaged, the signals do not travel down the nerves normally.
Hypotonia can also occur in disorders that affect the body’s connective tissue, such as Marfan syndrome and Ehlers-Danlos syndrome (see below).
Connective tissue, such as collagen, provides the body’s tissues with strength and support. It is found in ligaments and cartilage.
Some of the many health conditions that can cause hypotonia are described below.
Hypotonia present at birth (or shortly after)
Hypotonia present at birth or shortly after can be caused by:
- Cerebral palsy: several non-progressive neurological (brain-related) problems that are present at birth and affect a child's movement and co-ordination.
- Brain and spinal cord injury: including bleeding into the brain.
- Serious infections: such as meningitis (an infection of the outside membrane of the brain) and encephalitis (an infection of the brain itself).
- Genetic and chromosomal disorders: such as Down’s syndrome (a genetic disorder that is present at birth and affects a person's normal physical development and causes learning difficulties), Prader-Willi syndrome (a rare genetic condition that causes a wide range of symptoms including permanent hunger, restricted growth and learning difficulties)) and Tay-Sachs disease (a rare and usually fatal genetic disorder that causes progressive damage to the nervous system).
Read more about genes and chromosomes.
Hormonal and metabolic disorders
- Congenital hypothyroidism: where a baby is born with an underactive thyroid gland. In the UK, babies are screened for this and treated early.
- Rickets: a condition where the normal development of the bones is affected due to a lack of vitamin D and/or calcium. Rickets is a very rare but treatable cause of hypotonia.
Peripheral motor nerve disorders
- Spinal muscular atrophy: a genetic condition that causes muscle weakness and a progressive loss of movement.
- Charcot-Marie-Tooth disease: an inherited condition that affects the myelin covering of nerves.
Disorders that disrupt signals between nerves and muscles
- Myasthenia gravis: in adults, myasthenia gravis causes weakness and increased fatigue rather than hypotonia. Babies born to mothers who have myasthenia gravis may also be affected and if so will usually have hypotonia.
Disorders that affect the muscles themselves
- Muscular dystrophy: a group of genetic conditions that gradually cause the muscles to weaken, leading to increasing but variable levels of disability.
Connective tissue disorders
- Marfan syndrome and Ehlers-Danlos syndrome: both are inherited and are examples of conditions that affect connective tissues which provide support and structure to other tissue and organs.
Disorders causing muscle tone problems in adults
Disorders that cause abnormalities of muscle tone in adults include:
- Multiple sclerosis: where the myelin coverings of nerve fibres are damaged, which interferes with their ability to transfer signals.
- Motor neurone disease: a rare condition that progressively damages the motor nerves and causes the muscles to waste away.
Weakness and problems with mobility and balance are common in these conditions but muscle tone may also be affected.
If hypotonia is suspected in a newborn baby or young child, they will be referred to a specialist. This will usually be a specialist paediatrician or neurologist.
The specialist will start by asking you a number of questions which are likely to include:
- details about your pregnancy
- details about your delivery
- whether there have been any problems since the birth, such as seizures (fits)
- whether any other family members have had similar problems
Following the initial assessment, a full physical examination will be carried out. Some of the conditions that can cause hypotonia involve problems with other organs. A number of investigations will be suggested, including blood tests.
Other tests that may be recommended include:
- computerised tomography (CT) and/or magnetic resonance imaging (MRI) scans: these detailed scans can be used to detect any nervous system abnormalities or damage
- electroencephalogram (EEG): a painless test that records brain activity
- electromyography (EMG): where the electrical activity of a muscle is recorded using small needle electrodes that are inserted into the muscle fibres
- nerve conduction studies: where nerve activity is measured using small metal disc electrodes that are placed on the skin over the nerve
- muscle biopsy: where a small sample of muscle tissue is taken and examined under a microscope (read more about muscle biopsy)
- genetic testing: you or your child may be referred for genetic testing, which is a way of finding out whether you are carrying a particular genetic mutation (altered gene) that causes a medical condition (read more about genetic testing and support)
In some cases of hypotonia, no underlying cause can be found despite carrying out exhaustive tests. This is sometimes referred to as "benign congenital hypotonia". However, this is a rather controversial term and some experts recommend ongoing follow-up in such cases.
The recommended treatment plan for hypotonia (decreased muscle tone) will depend on the underlying cause.
Hypotonia that is caused by a baby being born prematurely will usually improve as the baby gets older. However, specialist treatment and support may be needed during this time and for other problems associated with prematurity.
Hypotonia in babies born to mothers with myasthenia gravis (a condition that causes weakness in certain muscles) usually improves quickly. Again, specialist treatment and support may be needed while the baby improves.
In cases where hypotonia is caused by an infection, the symptoms may disappear if the infection can be successfully treated.
If it is not possible to cure the underlying cause of hypotonia (as is unfortunately often the case) the two main treatments will be physiotherapy and occupational therapy.
In treating hypotonia, the main objectives of physiotherapy are to:
- improve posture and co-ordination to compensate for low muscle tone
- strengthen the muscles around the joints of the arms and legs so that they provide more support and stability
The physiotherapist will ask you to perform a series of exercises and tasks. They will also teach you a range of exercises that you can do on a daily basis.
Read more about physiotherapy.
Occupational therapy teaches you the skills that are needed to carry out day-to-day activities. For example, the occupational therapist will focus on improving the hand and finger skills that are needed for dressing and feeding.
As with physiotherapy, you will be asked to attend regular occupational therapy sessions. You will receive training so that you can perform exercises and tasks on a daily basis.
Read more about occupational therapy.
Speech and language therapy (SLT)
Speech and language therapy (SLT) may be recommended in cases where speech and swallowing problems are associated with hypotonia. SLT can also help to develop better control of the jaw and mouth muscles.