Hypotonia Defined

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Hypotonia is not a diagnosis, rather it is  a symptom of diminished tone of skeletal muscle associated with decreased resistance of muscles to passive stretching.  So, what does this complicated definition mean?

Although we are not always aware of it, our muscles receive continuously information and instructions from our brain, whether to relax or to contract and build up tension.  The precise combination of contraction in some muscles and relaxation in others enables us to keep in a certain position or posture.  If this balance of muscle tone is altered we are able to change from that particular position and move parts of our body.  For example, if you are trying to throw a ball you first have to bend your arm; this requires your biceps muscle to contract and your triceps muscle to relax.   You subsequently have to straighten your arm to throw the ball; your biceps muscle has to relax a little bit and your triceps muscle will have to contract, so the ball can be thrown.

In general, muscles of children with low tone are slower to respond to the contraction stimuli they receive from the brain.  In addition, they are often not able to maintain the intensity of the contraction for an extended time period.  Together, this causes children to not be able to sit independently, crawl or even stand and walk.  Later in life, this may lead to various motor dysfunctions such as an unusual insecure body habitus, inability to run and/or the inability to take stairs independently.

It is important to note that low muscle tone does not mean decreased muscle strength.   However, often, hypotonia and muscle weakness go together and it is clinically very important to distinguish these two from each other as different diagnostic and therapeutic strategies are required for disorders associated with hypotonia and muscle weakness.  For example, patients who have hypotonia and decreased muscle strength are most likely not going to benefit from sensory integration treatment techniques (repetitive sensory stimuli to improve the brain’s ability to perceive changes in muscle length) because the skeletal muscle may simply not have the ability to respond appropriately to these repetitive stimuli. 

We are therefore striving to gain insights into the natural course of hypotonia in various disorders in order to select the appropriate diagnostic and therapeutic path beneficial to the individual patient.