Hypotonia is the medical term for 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 tone in their back and neck muscles 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 be difficult to use the affected muscles. Muscle weakness sometimes develops in association with hypotonia, however, depending on the cause.
The condition is most often detected in babies soon after birth or at a very young age, although it can also develop later in life.
Signs and symptoms of hypotonia
Hypotonia present at birth is often noticeable by the time a child is six months old, if not before. Newborn babies and young children with severe hypotonia are often described as being "floppy" or like a "rag doll".
Specific signs of hypotonia in a child can include:
having little or no control of their neck muscles, so their head tends to flop
feeling limp when held, as though they could easily slip through your hands
being 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
finding sucking and swallowing difficult, and they may have a weak cry
A child with hypotonia may also take longer to reach developmental milestones, such as sitting up, crawling, walking, talking and feeding themselves.
An adult with hypotonia may have the following problems:
becoming clumsy and falling frequently
difficulty 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 objects
Why it happens
Hypotonia is a symptom rather than a condition itself. It can be caused by a number of different underlying health problems, 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).
In some cases, babies born prematurely (before the 37th week of pregnancy) have hypotonia because their muscle tone is not fully developed by the time they are born.
Testing for hypotonia
If hypotonia is suspected in your child, they will be referred to a specialist health professional who can try to identify the cause. The specialist will ask questions about your family history, your pregnancy, delivery and any problems that have occurred since birth.
A number of tests may also be recommended, including blood tests, acomputerised tomography (CT) scan or a magnetic resonance imaging (MRI) scan.
How hypotonia is treated
Depending on the cause, hypotonia can either improve, stay the same or get worse over time.
Babies with hypotonia caused by being born prematurely will usually improve as they get older. Babies with hypotonia caused by an infection or another condition will usually improve if the underlying condition is successfully treated.
Unfortunately, it's often not possible to cure the underlying cause of hypotonia. Hypotonia that is inherited will persist throughout a person's life, although treatment can help improve functions such as mobility and speech.
In these cases, treatment may involve physiotherapy, occupational therapy and speech and language therapy.
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Causes of hypotonia
Hypotonia (decreased muscle tone) is a symptom rather than a condition. It can be caused by a number of underlying problems.
One main problem that can cause hypotonia is disruption of the signals between nerves and muscles.
To function normally, muscles depend on signals from motor nerves. These signals can become disrupted at the level of the brain and spinal cord (known as "central hypotonia"), or as a result of nerve damage between the spinal cord and muscle (known as "peripheral hypotonia").
Other problems that can cause hypotonia include:
disorders affecting hormones and other substances essential for muscles to work properly
disorders of connective tissue – connective tissue, such as collagen, provides the body's tissues with strength and support, and is found in ligaments and cartilage
being born prematurely (before the 37th week of pregnancy) – premature babies sometimes have hypotonia because their muscles are not fully developed by the time they are born
Examples of some of the many health conditions that can cause hypotonia are described below, although some of these are rare.
Conditions that cause hypotonia
Hypotonia in babies and young children
Some of the conditions that can cause hypotonia in newborn babies and young children include:
cerebral palsy – several non-progressive neurological (brain-related) problems present at birth that 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)
Down's syndrome – a genetic disorder present at birth that 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
Tay-Sachs disease – a rare and usually fatal genetic disorder that causes progressive damage to the nervous system
congenital hypothyroidism – where a baby is born with an underactive thyroid gland; babies are screened for this and treated early in the UK
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 a substance called myelin that covers nerves and helps carry messages to and from your brain
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
muscular dystrophy – a group of genetic conditions that gradually cause the muscles to weaken, leading to increasing but variable levels of disability
Marfan syndrome and Ehlers-Danlos syndrome – inherited conditions affecting the connective tissues that provide support and structure to other tissue and organs
Hypotonia in later life
Although less common, hypotonia can develop in older children and adults. This can be caused by some of the problems listed above, but other possible causes include:
multiple sclerosis – where the myelin coverings of nerve fibres are damaged, interfering 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 (decreased muscle tone) is suspected in a newborn baby or young child, they will be referred to a specialist.
This will usually be a paediatrician (specialist in treating children) with expertise in disorders of the nerves and nervous system, or a neurologist (specialist in disorders of the nerves and nervous system).
The specialist will start by asking 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) or feeding difficulties
whether any other family members have had similar problems
Following the initial assessment, a full physical examination will be carried out and a blood test may be offered.
Other tests that may be recommended include:
computerised tomography (CT) scans 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 using small electrodes placed on the scalp
electromyography (EMG) –where the electrical activity of a muscle is recorded using small needle electrodes inserted into the muscle fibres
nerve conduction studies –where nerve activity is measured using small metal disc electrodes placed on the skin over the nerve
muscle biopsy – where a small sample of muscle tissue is taken and examined under a microscope (see diagnosing muscular dystrophy for more information 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.
In some cases of hypotonia, no underlying cause can be found despite exhaustive tests. This is sometimes referred to as "benign congenital hypotonia". However, this is a rather controversial term and some experts recommend further tests in such cases.
The recommended treatment plan for hypotonia (decreased muscle tone) will depend on the underlying cause.
Hypotonia 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. Speech and language therapy may also be used.
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 they provide more support and stability
You may be offered regular sessions with a physiotherapist, who will ask you or your child to perform a series of exercises and tasks. They will also teach you a range of exercises you can do on a daily basis.
Occupational therapy teaches you the skills needed to carry out day-to-day activities. For example, the occupational therapist will focus on improving hand and finger skills needed for dressing and feeding.
As with physiotherapy, you may be offered regular occupational therapy sessions. You will also be taught exercises and tasks you can perform on a daily basis.
Equipment to help you move around easier may also be recommended, such as ankle or foot supports if your ankles are affected by hypotonia.
Speech and language therapy
Speech and language therapy involves being taught a range of techniques by a speech and language therapist (SLT) to help improve any speech or swallowing problems sometimes associated with hypotonia. For example, you may learn exercises that help improve the strength of your swallowing muscles.
Speech and language therapy can also help you develop better control of your jaw and mouth muscles if these are affected by hypotonia.