Rethinking low muscle tone

Low muscle tone is often frequently used by therapists as a reason for a child’s movement dysfunction, and intervention is directed towards improving the muscle tone.

The problem is that there is no clearly defined way of defining or measuring low muscle tone. The diagnosis as it were is usually given when a child appears less able to effectively sustain an erect posture in sitting or standing, has delayed motor development or has difficulty performing age appropriate tasks.

I would like to suggest the physiotherapists stop using this term altogether and rather start to characterize a child’s movement difficulties more accurately by assessing to identify underlying impairments such as joint hypermobility, weakness, and specific difficulties with postural control and movement coordination.

For a more detailed discussion go to the rethinking low muscle tone page on the Skills for Action website

As a way of getting the debate going, here is a scenario of Xola, a 10 month old, infant who has been diagnosed as having low muscle tone.

At 10 months Xola cannot sit without some support. Her mom always supports her head when she picks her up, and Xola tends to lean into her mother when she sits on her lap. She is a shy child who is happy to interact with me when she is sitting on her mother’s lap. It took a little coaxing to get her to sit on the floor with support, and then played happily with the toys I provided banging them together, doing lots of shaking, looking at the toys intently, fingering them and bringing them to her mouth. She also enjoyed playing peek-a-boo with me.

Xola can roll over and on occasion will roll across the floor to retrieve a toy. She does not like being in prone, and does not push up into the hands-and-knees position.


What would your first thoughts be when you see this child? What would you assess? How would you go about getting some idea about the reasons for her delay in learning to sit independently.

Please post your ideas – and lets start talking. I will add more information on request.

Well,


So, what is her accurate diagnosis,before making motor evaluation for her!

Thank you very much for your interest in this debate.

Like so many children with a similar picture - the "diagnosis" from the paeditrician is simply: developmental delay with low muscle tone. There are no concerns about muscle pathology or atypical brain development. There is nothing unusual in her history - full term, but somewhat floppy infant at birth.

She belongs to a large extended family with lots of uncle's and aunties who like to pick her up and play with her. She knows exactly how to get what she wants and cries when she is denied. I am sure you see lots of these in Palestine, as we do in Cape Town.

Also see http://skillsforaction.com/?q=node/83

What would your first move be in evaluating this infant?

Pam

Hi Pam,

I do not disagree with your questioning the term low muscle tone due to its various meanings and biomechanical definitions. However, I cannot be sure that weakness, joint hypermobility etc cover exactly what I mean when I clinically use the term "low muscle tone". I remember a course I attended years ago by Yvonne Burns in Queensland it being drilled into us that you cannot see low muscle tone, you must feel it. Perhaps, as we have classification of high muscle tone-through the Tardieu and Modified Ashworth Scale, low muscle tone may be given a rating on a scale that depicts the degree or severity at which a muscle is affected by "low tone" as it were. The MAI touches on it but there is probably too much room for clinical error, the NSMDA also touches on it, but again asks the examiner to rate, normal, to high or low tone.
I am just very aware that I have felt children with "low muscle tone" that to look at their movement patterns and assess muscle strength probably don't appear to have tone problems, so therefore under the task performance and impairments model may not come out with any problems, but you know, when that child becomes a teen or adult who had "low muscle tone" but were told by the physio they had no problems, they may develop issues. I am sure there is too much ramble here but don't have time now to read it over, I hope some of it makes sense.
Thanks for the thought provoking post, I look forward to the study that gives us more clarification.

Hi Phunphysio

Thank you for your response. I have some difficulty following your argument. I think it is useful to stick to what little evidence we have, as well as the tangible things that can be measures such as muscle strength and changes in functional performance.

The other point is that any resistance to passive elongation one may pick up in a muscle, in the absence of neurological disorder, is related the the connective tissue elements associated with joints and muscles, as well as the titin within the muscle. Both of these structures change in response to muscle loading ie strengthening activities.

There is always a functional reason for child receiving a "diagnosis" of low muscle tone. There will be some functional task the child has difficulty performing.

The purpose of assessment is to identify the tasks a child cannot do and then identify the possible underlying reason for performance, as well as the factors, including impairments that are limiting performance.

In my experience children with so called "low muscle tone' always have a mixture of weakness, some two joint muscle shortening, hypermobility and avoidance of activities that require physical and mental effort.

Training task performance, strengthening muscles, releasing tight structures, training endurance improves everyday function. But most important perhaps is that the child learns to put effort into tasks and becomes more active, and the parents start to expect more or the child.

If an adult presents with low muscle tone it is always associated with weakness of joint hypermobility, which is associated with pain.