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, although in some cases of hypotonia, muscle weakness can develop in combination with 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 - where the symptom of hypotonia is present at birth, and
- acquired hypotonia - where the symptoms of hypotonia develops 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 - which is 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), and
- dyspraxia - a poorly understood condition that causes problems with movement, coordination, and language.
For many children with congenital hypotonia, tests are unable to 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, and that it is simply a label that is used when a complete diagnosis cannot be made.
Acquired hypotonia can develop after an illness, infection, or injury causes damage to the brain and/or nervous system. For example, this can occur in conditions such as:
- muscular dystrophy - where 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, and
- myasthenia gravis - a condition where the immune system attacks healthy muscles.
How common is hypotonia?
It is difficult to estimate how many people are affected by hypotonia in the UK 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 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 of hypotonia do not usually get any 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 that are 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 will usually persist and may get worse over time.