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.

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.