CMT Is Not Muscular Dystrophy
Updated: Jan 18
There is a huge misconception that CMT is a form of Muscular Dystrophy (MD). CMT categorically is not MD. CMT is openly erroneously considered a form of MD because the Muscular Dystrophy Association (MDA) provides for CMT. People don’t like to look past that, including physicians and clinicians, to understand that the MDA is not a disease or a group of diseases.
Far too often, the MDA and MD are misrepresented and/or misconstrued to be the same thing, but the two are not. This misconception is fostered by untrained physicians and healthcare professionals, and is virally proliferated on the internet and on social media platforms. It’s unfortunate, because, if we don’t understand what kind of a disease CMT is, then there exists no reasonable way for us to care for the persons who have CMT.
MDA vs. MD
The MDA is a nonprofit organization that provides research, research funds, and patient care for individuals who have a disease that affects muscles. Some of these diseases are primary muscle diseases (these are the Muscular Dystrophies), some are diseases that are secondary muscle diseases (these are the neuromuscular diseases – CMT, Myotosis’, etc.), and some are motor neuron diseases (the ALS’s and SMA’s).
Simply put, MD is a group of diseases that are primary muscle diseases, that is, the muscles are directly diseased. The MDA is an organization that provides research, research funding, and patient care for many diseases. Some of these are Muscular Dystrophies, and many are diseases that are not any form of MD; but, the disease process subsequently affects the muscles. Examples of these non-MD diseases would be SMA, CMT, and ALS.
The MDA provides research, research funding, and patient care for every form of Muscular Dystrophy; and they also provide the same for more than 40 diseases that are not any form of MD. The standard nomenclature is, “The MDA covers under its umbrella….” Using the term, “umbrella,” is a misnomer though, insofar as an inference is created that is patently incorrect about every non-MD disease that the MDA “covers.” The inference is that everything they “cover” is a form of MD. To think so or believe so would be profoundly incorrect.
CMT vs. MD
CMT differs from MD insofar as CMT, in all forms, is a disease of the peripheral nerves and not the muscles, but the muscles suffer because of the disease process in the nerves. The muscle component/involvement in CMT is a byproduct of the peripheral nerves being diseased. Conversely, in all forms of MD, the muscles themselves are diseased, and are not affected as a byproduct of a disease process in a non-muscle piece of anatomy.
We don’t consider or assume ALS to be a form of MD, even though the MDA provides for ALS. So, why, for all that is good, do we assume or accept that CMT is a form of MD because the MDA provides for CMT, especially when CMT is clearly not a Muscular Dystrophy?
CMT, in all of its forms, types, and subtypes, is not any form, type, or subtype of any Muscular Dystrophy. MD is a muscle disease. CMT is a peripheral nerve disease that affects muscles, secondary to the peripheral nerves. The MDA even clearly and plainly details these differences in their publications and on their websites. They also clearly list the Muscular Dystrophies, and they clearly label and list all of the Non-Muscular Dystrophies. The Non-MDs even get their own section. This section has many diseases, including CMT, ALS, etc. However, we still struggle with this one thing that shouldn’t even be a thing.
Nope, I Need an Example
No matter how we wrap it, CMT, in every form and in every person, is a disease of the peripheral nervous system. The nerves are diseased, not the muscles. I’ll use myself as an example, and then I’ll use a couple of metaphorical analogies for a great visual aid, so that I can clarify the intrinsic difference.
I have CMT1A. Every skeletal muscle of mine is affected. Feet, legs, arms, hands, diaphragm, respiratory accessory muscles, throat, speech, neck, back— everything. But, it’s the nerves that are diseased, not the muscles. My muscle issues exist because the nerves that control them are diseased. Specifically, my peripheral nerves are what’s diseased.
The peripheral nervous system is the go-between for the brain/spinal cord and the muscles. When the peripheral nerves are diseased to the extent that they are in CMT, everything that is controlled by the peripheral nerves eventually becomes affected. But, the things that are controlled by the peripheral nerves (all of the muscles) are not themselves diseased. I’ll use a lamp and lamp cord analogy to help illustrate this.
With a lamp, envision that the light bulb is the muscles. The electrical outlet in the wall is the spinal cord/central nervous system. The lamp cord that plugs into the wall is the peripheral nerve/peripheral nervous system. When the lamp cord becomes damaged (it’s sheathing wears out, or the wires inside become damaged), the light bulb will have problems working. The electrical signal coming from the wall gets impeded. In turn, the bulb may flicker. It may be dim. It may all of a sudden brighten, and then go off, etc. However, the light bulb is actually perfectly fine. The wire that controls it is damaged. If we put the bulb in a lamp without a damaged cord, the bulb functions perfectly. If we replace the light bulb, it still functions poorly. The new bulb functions poorly because it’s the bad wires of the lamp cord causing the issues, and not the bulb. This is how every form, type, and subtype of CMT works. The muscle dysfunction in CMT, much like the light bulb acting funny because of an impaired lamp cord, is the result of impaired nerves.
In Muscular Dystrophy, if we use the same lamp analogy, the bulb is what is bad. If we drop in a new bulb, it functions fine because the wires that supply it are not damaged. The signals trying to reach the bulb are not impeded.
The lamp metaphor and analogy is an over simplification, of course. But, it provides a good visual aid for understanding how the systems work together. Another good visual reference is a garden hose connected to a sprinkler.
Envision that a garden hose is a peripheral nerve. At one end, it’s connected to the faucet (the spinal cord/central nervous system). The other end is connected to a sprinkler (the muscle). When you turn on the faucet, the hose fills with water (the water is the nerve impulse that will cause the muscle to work). With a perfectly fine tip-top hose, the sprinkler comes on right away, waters the lawn or garden perfectly, as needed, and all is well. If the hose gets a kink in it though, or has a bunch of holes, or is otherwise damaged, the sprinkler will not work as well. Sure, it will still do its thing, sort of, but it won’t do it as well, and it’ll take far more water volume (energy) to do it.
In this metaphor and analogy, the sprinkler (muscle) is perfectly fine. The hose though (the nerve), is damaged, causing the sprinkler to not work as well. This, too, is an oversimplification, but it provides a good visual reference.
In the two examples, Muscular Dystrophy would be the end chain – the light bulb and the sprinkler – being damaged, and not what controls them – the cord or the hose. If we change the bad bulb or the bad sprinkler, the problem is solved. With CMT, the cord or hose is damaged. Changing the bulb or the sprinkler wouldn’t solve the problem – the bulb or the sprinkler would still function poorly. Therein lies the intrinsic difference between MD and CMT, and why CMT is not MD, in any form.
I know the metaphors and analogies I used are a gross oversimplification of a highly complex biological mechanism. They do, however, perfectly illustrate the respective disease processes and the core differences between CMT and MD. CMT is a case, in all its forms, of diseased nerves, not diseased muscles. The muscles are affected and become what they become, not because of a disease in the muscles, but because the nerves that control them are diseased.
CMT is extremely complex and widely varied. In some subtypes, the myelin (nerve sheath) of the peripheral nerve is damaged. In others, the axon (nerve wire that transmits the signals) is damaged. Yet, in others, it’s a mitochondrial dysfunction that damages the peripheral nerves. Whatever the disease process, the transmission of impulses and information to and from the spinal cord is impaired and slowed down in CMT. This impaired slowing down of impulses in and through the peripheral nerves is what causes all of the muscles to do what they do in CMT. Again, the muscle issues are a result of the disease process in the nerves that control them, and not the result of a disease process inside the muscles.
In any disease of the peripheral nervous system, or if just a single peripheral nerve becomes damaged or diseased, whatever that nerve or nerves control will be affected. But, what is diseased or damaged is the nerve, and not what is being controlled.
In the end, CMT, in all its forms, types, subtypes, and presentations, is a peripheral nerve disease. This nerve disease, in turn, affects everything that the nerves connect to and control. What the nerves connect to is not diseased though.
Of all the CMT misconceptions being fostered by the medical community and thereafter proliferated by the masses, the misconception that CMT is a form of Muscular Dystrophy is the most difficult to overcome, and I am intensely passionate about correcting the misconception. CMT is not MD.