I was reading through Jan's diet, and a few of her responses to other people's questions, and I kept wondering about the role of potassium in MC?

I suffer cramps ranging from annoying to debilitating and my neurologist suggested an increase in potassium, in particular eating bananas, as a means of relieving the worst of the muscles spasms. Since I started eating at least one banana a week I’ve not had a serious seizure, which is a relief.

However, is this at the expense of worse MC symptoms?

As I’m on Mexilitine I’m not sure if I can answer this question. I still seem to have good and bad days even on meds, but even on the bad days my symptoms are no way near as bad as they are without the Mexilitine.

I’m quite interested in the science behind this, although I must admit to being a total amateur in this respect. I understand about the function of the channels for letting sodium/chloride ions into the muscle cells, but what is the role of potassium?

Type of Myotonia: Becker's

Country: England

Pete,

When you say seizure to you mean muscle cramping or the type of seizure like you'd get with epilepsy?

Mexiletine does change electrolyte balances and one of the routine tests you should have is serum potassium.

We have to have potassium to survive and most of us get plenty in our diet, even if we avoid the high potassium foods. However if you are eating a lot of salt or if you have other medical conditions you may need more to compensate. I would still avoid the potassium additives like potassium iodide, potassium nitrate, potassium sorbate, etc.

Mexiletine is a potentially very dangerous drug if it is not administered and monitored by a skilled doctor. You should have a product insert which lists all the side effects to watch for and all the drugs that can interact with it. For instance it is often recommended to take it with an antacid, and yet sodium bicarbonate and magnesium-aluminum oxide, very common antacids, are contraindicated. If you drink coffee you will excrete 50% less caffeine when using mexiletine and this could overstimulate your adrenals, making the myotonia worse.

Mexiletine works by blocking the sodium channel and opening the potassium channel. This helps move the potassium from the extracellular position to the channels where it belongs and allows the muscles to repolarize or recover from contracting sooner. It does not directly stimulate the chloride channel which would be the ideal medication, but in a roundabout way it helps.

There are channels for chloride, potassium, sodium and calcium. Our condition is called a channelopathy which means one or more of the subunits of the chloride ion channel are affected. This is going to be dependent on your particular mutations. In Becker's you have two so the potential for even more inhibition is there.

You might want to read the Quest magazine article on the web page to see more about how the chloride channel functions. There are definitely going to be times when your potassium levels are low whether you're on medication or not. And when that happens it can be helpful to drink orange juice, eat a banana, etc but in general if you consume those foods on a regular basis they may be making the MC worse, partly because of the potassium but also because high-potassium foods also tend to be simple carbohydrates that stimulate the output of insulin.

Some of the symptoms of low potassium are weakness, fatigue, muscle cramps, constipation and heart arrhythmias. Of cours some of those are symptoms associated with MC, too, so it can be hard to differentiate. The only way to know for sure is to get a serum potassium test when you're having the symptoms.

You are most likely to experience lower potassium levels after you've eaten a high carbohydrate meal, done fairly strenuous exercise, eaten quite a bit of salt, or if you have higher than normal thyroid production. One of the goals for either high or low potassium is to maintain stable blood sugar levels. You do this by eating good quality protein throughout the day, eating a moderate amount of healthy oils in your diet, and avoiding sugar and simple carbohydrates.

The diet recommendations are foremost aimed at stabilizing blood sugar. If you do this then the potassium levels will not be as much of a problem. You might want to take notice if the cramping is more noticeable after eating foods containing sugar or after exercise (which increases insulin production and increases extracellular potassium).

The weakness associated with low potassium is not just where you don't feel as strong, but it's actually hard to move. There is no stiffness, but rather a sensation that your muscles weigh a ton and you're just too tired to move them. For people with hypokalemic periodic paralysis it can actually become impossible to voluntarily move their arms and legs for a period of time. The body is constantly working to balance all these electrolytes and ion channel functions so it eventually tends to even out after a few hours, but it can be scary to experience the paralysis.

By the way, mexiletine is structurally very close to lidocaine, a commonly used anesthetic which can make hypokalemia much worse.

Jan

Type of Myotonia: Thomsen's MC

Country: US

Thanks for that extensive reply Jan, it made fascinating reading.

The seizures are really cramps but they can be very severe, the worst I've ever had involved every skeletal muscle in my body. My doctor tends to refer to them as seizures, which I can see could be confusing now.

I had a blood test done last year but that was the first one I’ve had since starting on Mexiletine, which I’ve been using for some time now. Although I have the product insert I was not aware about issue with caffeine; fortunately I don’t drink a lot of coffee in a normal day.

I have read the Quest magazine article, in fact I’ve edited it down and gave it to my current employer as a fact sheet. They were very appreciative and I now benefit from a much more positive attitude because they understand the nature of my complaint and, I believe, now know that MC is scientifically recognised and not just in my imagination!

I don’t eat a lot of salt and exercise is limited to physiotherapy, it tones my muscles which is of benefit, but it doesn’t give me a strenuous workout. My wife is good with food management so I’ll get her to look at the carbohydrate content of our meals. In fact I’m going to show her your reply, she’s a student nurse (final year) and I know she’ll be interested in understanding my condition better.

I do suffer the muscle weakness; sometimes my arms are just too heavy to hold over my head, they just collapse. I’ve also had situations when I can’t move my arms, it feels like there’s just no strength there at all. However, I can’t say that this symptom has got any worse since starting on the Mexiletine.

Again, thanks for your very comprehensive reply.

Type of Myotonia: Becker's

Country: England

I am a newly diagnosed myotonia sufferer. I've experienced muscle symptoms all my life, but have found that the symptoms are getting worse. I am an RN, who was injured on the job and haven't been able to work for quite a while now. Since discovering this site I've had a lot of "pieces of the puzzle" fit. It is nice to finally have proof that I am not crazy. My main concern right now is my youngest daughter. She is having headaches originating at the base of the skull and into her neck that are unrelieved, tingling in her hands and now legs, can't sleep etc... She also has a history of minor injuries (sprains, strains). I strongly suspect MC, but getting her neurologist to do a DNA test has been difficult. Just a couple of days ago he prescribed a "happy" pill and told me he thought she was depressed. I can tell you she is not, but he won't listen. I didn't give her the meds, because she doesn't need them and I'm a little gunshy until I know what is going on. Does anyone have any thoughts?

Type of Myotonia: unkown

Country: USA

Jodi,

If one of you gets a positive DNA test, then all that's needed to confirm MC from that point is a quick EMG to detect myotonic discharges.

You might want to contact the closest MDA clinic and see if they have any funds for testing. Since you don't know your type it could be either MC or paramyotonia congenita or some other rare form of myotonia. The DNA test from Athena, myotonic profile, would help differentiate. I think the MDA sends most of their tests to that lab.

One thought about your daughter. If she has hypermobility or is "double jointed" or extremely flexible, you could have a rheumatologist check her for a condition called Ehlers-Danlos Type III. It's totally unrelated to MC but I happen to have both and so does one of my daughters with MC. It's not that rare, just seldom diagnosed. It can cause subluxations of joints and constant sprains and joint strains. It indirectly affects the muscles but is not a muscle disease.

There is also the possibility of myotonic muscular dystrophy in your family which affects muscles, heart, GI tract, endocrine system, etc. Again, the Athena testing would confirm or rule out this type.

I'm glad you're refusing the "happy pills." It so dangerous to give them to children and teens. Any chance you can get a different doctor?

Jan

Type of Myotonia: Thomsen's MC

Country: US