Hypotonia is a medical term for decreased muscle tone. If you have decreased muscle tone, your muscles will take on a floppy, 'rag-doll' appearance and you may have problems using the affected muscles.
Healthy muscles are never fully relaxed as they retain a certain amount of tension to allow them to be used when needed. This tension is known as muscle tone. Decreased muscle tone is not the same as muscle weakness. However, in some cases of hypotonia, muscle weakness can develop alongside decreased muscle tone.
Types of hypotonia
Hypotonia is not a condition in itself. It is a symptom of another underlying condition.
There are two main types of hypotonia:
- congenital hypotonia - the symptom of hypotonia is present at birth
- acquired hypotonia - the symptoms of hypotonia develop after birth as the result of an underlying medical condition, injury or trauma
Congenital hypotonia is usually caused by genetic (inherited) conditions that disrupt the normal development of the nerves, muscles and brain.
Genetic conditions that are known to cause congenital hypotonia include:
- Down's syndrome - the most common cause of congenital hypotonia
- Marfan syndrome - a condition that affects the connective tissue (a layer of tissue that helps to maintain your body's structure and integrity by supporting the bones, muscles and organs)
- dyspraxia - a poorly understood condition that causes problems with movement, co-ordination and language
For many children with congenital hypotonia, tests cannot find any evidence that they have an underlying condition. This is sometimes referred to as benign congenital hypotonia (BCH).
However, BCH is a controversial term that is not accepted by all health professionals. Some experts argue that BCH is not a proper diagnosis but simply a label that is used when a complete diagnosis cannot be made.
Acquired hypotonia can develop after an illness, infection or injury damages the brain and/or nervous system. For example, this can occur in conditions such as:
- muscular dystrophy - there is a gradual weakening and damage of the muscles (this is the most common cause of acquired hypotonia)
- serious infections, such as meningitis, which is an infection of the outside membrane of the brain, or encephalitis, which is infection of the brain itself
- a serious head injury
- myasthenia gravis - a condition where the immune system attacks healthy muscles
How common is hypotonia?
It is difficult to estimate how many people in England are affected by hypotonia because it can be caused by so many different conditions.
What is known is that although many of the conditions that cause hypotonia are uncommon, they are certainly not rare. For example, 600 babies are born with Down's syndrome in the UK each year, and there are 2,000 cases of bacterial meningitis (the most serious type of meningitis) in England and Wales.
The outlook for cases of hypotonia depends on the underlying cause.
For most types of congenital hypotonia, a cure is not possible and the symptoms of hypotonia will persist for the rest of a person's life. However, the symptoms do not usually get worse as a person gets older.
While congenital hypotonia cannot be cured, the symptoms can be improved with treatment, such as physiotherapy and occupational therapy (therapy that is designed to improve the skills and abilities needed for daily activities).
In cases of acquired hypotonia that are caused by infection, the symptoms of hypotonia may disappear after the underlying infection has been treated.
In cases where acquired hypotonia is caused by a serious, chronic health condition, such as muscular dystrophy, the symptoms of hypotonia usually persist and may get worse over time.
Symptoms of hypotonia
The signs and symptoms of congenital hypotonia usually become noticeable by the time a child is six months old. Signs and symptoms include:
- your child has little or no control of their head
- your child feels limp when you hold them; they feel as though they could slip through your hands
- your child is unable to place any weight on their leg or shoulder muscles
- your child's arms and legs hang straight down from their sides, rather than flexing at their elbows and knees
- your child may slip or fall out of a high chair
- your child may find feeding difficult
In cases of congenital hypotonia, intelligence is usually unaffected (with the exception of Down's syndrome). However, your child may be slower in reaching 'developmental milestones', such as learning to:
- sit up
- being able to feed themselves
The time that it takes for the symptoms of hypotonia to progress will depend on the underlying cause. For example, acquired hypotonia that is caused by illness or infection can develop over the space of a few hours or days.
Acquired hypotonia that is caused by a long-term condition, such as muscular dystrophy, or myasthenia gravis, can develop over the space of many months or years.
In acquired hypotonia, the symptom of decreased muscle tone remains unchanged. However, it can make itself known in different ways when it develops during adulthood rather than childhood. For example:
- suddenly becooming unusually clumsy
- falling frequently
- difficulty getting up from a lying or sitting position
- your hips, elbows and knees begin to feel unusually flexible
- you have difficulty stretching to reach something, or lifting an object.
Causes of hypotonia
Hypotonia can be caused by damage to:
- the brain
- the nervous system
- the muscles themselves
Some common causes of congenital and acquired hypotonia are outlined below.
Neuromuscular conditions are conditions that interrupt the signals, which are sent to the brain via the nervous system to the muscles. This leads to the muscles not functioning properly.
Examples of neuromuscular conditions include:
Chromosomal disorders are genetic conditions that are caused by problems with chromosomes.
Chromosomes are clusters of cells that contain detailed genetic information, which you inherit from your parents. They are responsible for controlling a wide range of factors - from the colour of your hair, to how the cells in your body develop.
Chromosomal disorders can develop if there is a mutation (an alteration) in one of the chromosomes, or you inherit too many or too few chromosomes from your parents.
Examples of chromosomal disorders include:
- Down's syndrome
- Prader-Willis Syndrome - a rare genetic condition that also causes learning difficulties
- Williams Syndrome - a rare genetic condition that causes problems with development, co-ordination and language
Metabolic disorders are health conditions that disrupt the normal workings of the body's metabolism. Metabolism is a term that describes all of the chemical reactions that are used by the body to break down food into energy.
Metabolic disorders can cause a chemical imbalance in the body. This in turn can affect the normal workings of the muscles.
Examples of metabolic disorders include:
- congenital hypothyroidism - a condition where a baby is born with an underactive thyroid gland (the thyroid gland plays an important role in regulating the body's metabolism)
- rickets - a condition that affects the normal development of the bones.
Connective tissue disorders
Connective tissue disorders are health conditions that interfere with the normal production of connective tissue. Connective tissue is a tough, fibrous tissue found in many parts of the body, such as your ligaments, tendons, and around your organs. Connective tissue holds your organs in place.
Examples of connective tissue disorders include:
- Marfan syndrome - a rare condition that affects the normal development of the body
- Ehlers-Danlos syndrome - a rare condition that causes problems with the muscles, joints and skin
Cerebral hypotonia is a general term that refers to symptoms of hypotonia that have been caused by damage to the brain.
Cerebral hypotonia can be caused by:
- a severe head injury
- a lack of oxygen to the brain due to a stroke or near-drowning
- infections of the brain, such as encephalitis
As hypotonia can be caused by so many different factors, a wide range of tests may be required to discover the underlying cause of you or your child's symptoms. However, in many cases of congenital hypotonia, no underlying cause can be found.
The tests that may be used in cases of hypotonia are described below.
- Complete blood count (CBC) - a type of blood test that measures the amount of blood cells in the blood. A CBC is a good way of assessing whether the blood circulation system is working as well as it should, and whether there is an infection in the body.
- Metabolic panel is a series of blood tests that are used to check whether the body's metabolism is working properly.
- Gene testing involves extracting a sample of each genetic chromosome from the blood and checking each chromosome for any problems.
- Computed tomography (CT) and magnetic resonance imaging (MRI) scans can detect any abnormalities or damage in the brain and nervous system.
- Electroencephalogram (EEG) is a test that is used to measure the electrical activity of the brain. Unusual activity would normally suggest that there is an underlying problem with the brain.
- Electromyography (EMG) is a test where electrodes are placed on the skin. The electrodes can be used to measure how nerve signals are passed through the muscles. An EMG can often detect whether part of the nervous system is 'blocking' the signals from the brain to the muscles.
- Muscle biopsy involves removing a small sample of muscle tissue, usually from the thigh. The tissue is studied under a microscope to see whether there are any abnormalities or tissue damage.
The recommended treatment plan for hypotonia will depend on the underlying cause. If the underlying cause is treatable, such as an infection, the healthcare professional will focus on treating that first.
If the underlying cause is untreatable, then the two main treatments that are used for hypotonia are:
- occupational therapy
Physiotherapy has two important goals:
- to improve the posture and co-ordination to compensate for low muscle tone
- to strengthen the muscles around the joints of the arms and legs so that they provide more support and stability for the arms and legs.
Physiotherapy usually involves attending a session with a physiotherapist every month. They will ask you or your child to do a series of exercises and tasks. The physiotherapist will also teach you or your child a range of exercises that can be done on a daily basis.
Occupational therapy aims to teach you new skills in order to help you with day-to-day activities. The therapist will focus on improving the skills that are needed to carry out tasks requiring a degree of manual dexterity, such as getting dressed, writing or using a computer.
As with physiotherapy, you will be asked to attend regular occupational therapy sessions. You will receive training so that you can do exercises and tasks on a daily basis.
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