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