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 posture when standing or sitting up. Muscle tone decreases during sleep, so if you fall asleep sitting up you may find that you wake up with your head flopped forward.
Hypotonia is not the same as muscle weakness, although it can be difficult to use the affected muscles. Muscle weakness sometimes develops in association with hypotonia, however, depending on the cause.
The condition is most often detected in babies soon after birth or at a very young age, although it can also develop later in life.
Signs and symptoms 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" or like a "rag doll".
Specific signs of hypotonia in a child can 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, and they may have a weak cry
A child with hypotonia may also take longer to reach developmental milestones, such as sitting up, crawling, walking, talking and feeding themselves.
An adult with hypotonia may have the following problems:
- becoming clumsy 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
Why it happens
Hypotonia is a symptom rather than a condition itself. It can be caused by a number of different underlying health problems, many of which are inherited (passed on from one family member to another).
It can also occur in cases of cerebral palsy, where a number of neurological (brain-related) problems affect a child's co-ordination and movement, and after serious infections such as meningitis (an infection of the outside membrane of the brain).
In some cases, babies born prematurely (before the 37th week of pregnancy) have hypotonia because their muscle tone is not fully developed by the time they are born.
Read more about the causes of hypotonia.
Testing for hypotonia
If hypotonia is suspected in your child, they will be referred to a specialist health professional who can try to identify the cause. The specialist will ask questions about your family history, your pregnancy, delivery and any problems that have occurred since birth.
A number of tests may also be recommended, including blood tests, a computerised tomography (CT) scan or a magnetic resonance imaging (MRI) scan.
Read more about how hypotonia is diagnosed.
How hypotonia is treated
Depending on the cause, hypotonia can either improve, stay the same or get worse over time.
Babies with hypotonia caused by 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 successfully treated.
Unfortunately, it's often not possible to cure the underlying cause of hypotonia. Hypotonia that is inherited will persist throughout a person's life, although treatment can help improve functions such as mobility and speech.
In these cases, treatment may involve physiotherapy, occupational therapy and speech and language therapy.
Read more about treating hypotonia.