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 position when standing or sitting up. Muscle tone decreases during sleep, so if you fall asleep sitting up, you may wake up with your head flopped forward.
Hypotonia isn't the same as muscle weakness, although it can be difficult to use the affected muscles. In some conditions, muscle weakness sometimes develops in association with hypotonia.
It is most commonly detected in babies soon after birth or at a very young age, although it can also develop later in life.
Signs 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".
Signs of hypotonia in a child 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
- a weak cry or quiet voice in infants and young children
A child with hypotonia often takes longer to reach motor developmental milestones, such as sitting up, crawling, walking, talking and feeding themselves.
An adult with hypotonia may have the following problems:
- clumsiness 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 (in cases where there's also muscle weakness)
What causes hypotonia?
Hypotonia is a symptom rather than a condition. It can be caused by a number of different underlying health problems, many of which are inherited.
Hypotonia can also sometimes occur in cerebral palsy, where a number of neurological (brain-related) problems affect a child's movement and co-ordination, and after serious infections, such as meningitis.
In some cases, babies born prematurely (before the 37th week of pregnancy) have hypotonia because their muscle tone isn't fully developed by the time they're born. However, provided there are no other underlying problems, this should gradually improve as the baby develops and gets older.
Read more about the causes of hypotonia.
If your child is identified as having hypotonia, they should be referred to a specialist healthcare professional, who will try to identify the cause. The specialist will ask about your family history, pregnancy and delivery, and whether any problems have occurred since birth.
Read more about how hypotonia is diagnosed.
Depending on the cause, hypotonia can improve, stay the same or get worse over time.
Babies with hypotonia that results from 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 treated successfully.
Unfortunately, it's often not possible to cure the underlying cause of hypotonia. Hypotonia that has been inherited will persist throughout a person's life, although the child's motor development may steadily improve over time in cases that are non-progressive (don't get worse).
Read more about treating hypotonia.
Causes of hypotonia
Causes of hypotonia
Hypotonia (decreased muscle tone) is a symptom rather than a condition. It can be caused by a number of underlying problems, which can either be neurological or non-neurological.
Neurological conditions are those that affect the nerves and nervous system. Hypotonia is most commonly linked to neurological control of muscle tone.
To function normally, muscles depend on signals from motor nerves. These signals can become disrupted at the level of the brain and spinal cord (central hypotonia), or as a result of nerve damage between the spinal cord and muscle (peripheral hypotonia).
Neurological conditions that affect the central nervous system and can cause central hypotonia include:
- cerebral palsy - neurological problems present at birth that affect a child's movement and co-ordination
- brain and spinal cord injury - including bleeding in the brain
- serious infections - such as meningitis (an infection of the outside membrane of the brain) and encephalitis (an infection of the brain itself)
Neurological conditions that affect the peripheral nervous system and can cause peripheral hypotonia include:
- muscular dystrophy - a group of genetic conditions that gradually cause the muscles to weaken, leading to increasing but variable levels of disability
- myasthenia gravis - a condition that causes weakness and increased fatigue rather than hypotonia in adults; babies born to mothers with myasthenia gravis may also be affected and, if so, will usually have hypotonia
- 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, which covers nerves and helps carry messages to and from the brain
Non-neurological problems that can cause hypotonia in newborn babies and young children include:
- 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 syndrome 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; in the UK, babies are screened for this and treated early
- Marfan syndrome and Ehlers-Danlos syndrome - inherited syndromes that affect the connective tissues that provide structure and support to other tissue and organs
- connective tissue disorders - 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 week 37 of pregnancy) - premature babies sometimes have hypotonia because their muscles aren't fully developed by the time they're born
Hypotonia in later life
Hypotonia can sometimes occur in older children and adults, although this is less common. It can be caused by some of the problems mentioned above, but other possible causes include:
- multiple sclerosis - where the myelin covering nerve fibres is damaged, interfering with their ability to transfer electrical signals from the brain and spinal cord to the rest of the body
- 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 also common with these conditions.
If hypotonia (decreased muscle tone) is suspected in a newborn baby or young child, they'll be referred to a specialist.
This will usually be a paediatrician (a specialist in treating children) with expertise in disorders of the nerves and nervous system, or a neurologist (a 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 damage or abnormalities
- 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
- genetic testing - you or your child may be referred for genetic testing, which is a way of finding out whether you're carrying a particular genetic mutation (altered gene) that causes a medical condition
In some cases, no underlying cause can be found despite numerous tests. This is sometimes referred to as benign congenital hypotonia. In this situation, treatment and support can be offered to manage functional difficulties after other causes of hypotonia have been excluded.
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 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 is treated successfully.
If a cure for the underlying cause of hypotonia isn't possible - as is unfortunately often the case - treatment will mainly focus on trying to improve and support the person's muscle function through the use of physiotherapy, occupational therapy, and speech and language therapy. For example, orthotics and adaptive equipment may be required.
In some cases, funding may be available from social care services to help pay for things such as home adaptations, walking aids and wheelchairs. If additional support is needed at school, funding may also be available.
If physiotherapy is recommended, the physiotherapist will assess your child's muscle tone and ask them to carry out a series of exercises and tasks.
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
The physiotherapist will design a programme that includes a range of exercises for your child to do on a daily basis. Therapy should be fun and integrated into your child's daily routine and everyday activities, both at home and at school.
Occupational therapy teaches you the skills needed to carry out day-to-day activities. For example, the occupational therapist may focus on improving the hand and finger skills needed for dressing and feeding.
As with physiotherapy, you may be offered regular occupational therapy sessions. You'll also be taught exercises and tasks you can perform on a daily basis.
Equipment to help you move around more easily may also be recommended, such as ankle or foot supports if your ankles or feet are affected by hypotonia.
Speech and language therapy
A speech and language therapist (SLT) can assess your child's feeding and swallowing, and help identify swallowing problems that can sometimes be associated with hypotonia. The SLT will also be able to make recommendations about feeding support.