I would like to address the discussion of muscle tone, from my perspective and training as an OT. All medical professionals use the term "muscle tone" to refer to the same thing: the normal state of balanced contraction in muscle tissue. "Normal" muscle tone falls on a continuum. Some people have a higher resting state of contraction with a better and stronger contraction when they activate their muscles for movement while some have a lower resting state that requires more effort to activate a contraction for movement of a joint.
Our body uses pairs of muscles around every joint to maintain stability and activate movement. These are referred to as flexor muscles and extensor muscles. For both postural stability (such as staying seated in the chair with my hands on the keyboard as I type) and movement (my fingers as they fly over the keyboard) I must control my muscle tone through both voluntary and involuntary means - using my central nervous system (aka: brain)
Problems with muscle tone exist, as Lori and PTP have already discussed, in conjunction with many, many other disorders. We do, most often, think of people with brain injuries (CP, strokes, head trauma) who have very high or low muscle tone in one of side of the body or multiple extremities. What people often don't realize is that disorders of muscle tone do occur on a continuum and vary in their impact on daily life. Just as autism falls on a spectrum, a stroke can be mild, or someone has "mild diabetes," abnormal muscle tone can be "mild." That doesn't mean it doesn't impact on functional performance.
For many people, problems with muscle tone CAN be traced to a specific disorder, a head trauma, a metabolic disorder or other condition (see Lori's post). But there are some kids, adults even, who struggle with low muscle tone and DO NOT fit any of those categories. These are often the kids I see in my OT practice. I suspect that this is what the neurologist was referring to when he said that Lori's son's muscle tone was the result of his sensory processing disorder.
Sensory integration theory looks at the vestibular system as a primary component of the sensory integrative process - combined with the proprioceptive and tactile systems. This site has a great summary of vestibular processing:
http://nspt4kids.com/health-topics-conditions/vestibular-processing/As you can see, if you read about half way down, the vestibular system is directly linked to the activation of muscle tone. Developmentally we know that as an infant's position changes (by being held, moved, learning to roll over, being able to hold their up against gravity), the effect is that the vestibular system activates muscle tone. When we see a child in OT who has low muscle tone the intervention is highly movement oriented and includes LOTS of vestibular based activities that activate the system and facilitate muscle tone. We enhance the intervention by including proprioceptive and tactile input. We also know that including the visual and auditory systems into the loop further impacts vestibular processing. Neurological science reports that the vestibular system is linked to every lobe of the brain and impacts on almost every part of the central nervous system.
So this is how low muscle tone can be "a sensory processing issue." I see many children who are struggling with producing written work at school, unable to stay seated in their chairs, habitually lay down on the rug or against their friend during circle time, are unable to get dressed independently because they can't sit up unsupported or stand on one leg, or can't chew pizza because their jaw gets tired.
These children are deserving of treatment to improve the quality of their lives even if they don't present with severe CP or multiple handicaps. They may appear to be "normal" and be mistaken for a problem child who won't cooperate, won't sit still or is lazy. Their parents may be concerned that their child isn't going to make it through high school taking notes if they can't complete their first grade journal. Or worry about how they will be able to keep up with peers in gym class. Or wonder how they will ever get the nutrition they need if they only eat pudding and macaroni & cheese.
Some in our profession (and others) are postulating that our sedentary lifestyles are contributing to increased incidence of low muscle tone related to poor vestibular processing. Others suggest the toxins in our world or our diets. I've read articles that point out how detrimental it is for infants to be in car carriers for hours on end. And the "back to sleep" campaign has even been implicated in some articles - it limits tummy time and the natural change in head position that activates the vestibular system and facilitates the neck and back extensors, as well as ocular muscles that control fine eye movements.
I am glad to see the discussions even on this board, as the more people learn about it the better! I hope we can continue to discuss the issues and help with increasing awareness and understanding so everyone can get the help they need.
