Symptoms 

People who have potassium-aggravated myotonia suffer from attacks of myotonia, which is a stiff, rigid feeling of the muscles. This can happen in many different situations, including after performing simple actions like writing with a pencil. Patients with this disorder might have trouble loosening their fingers to let go of the pencil. Muscles all over the body can be affected, including facial muscles. For example, eyelids can be affected by myotonia, which means that patients will have difficulty keeping their eyes open.

The way all muscles move is by contracting, but thanks to a mutation in sodium channels in muscle cell membranes, myotonic muscles have a hard time relaxing after contracting. Fortunately, it’s usually possible to “work off” the stiff feeling with small, repetitive movements of the affected muscles. This may not be possible with severe attacks, but mild attacks can be worked off.

There are multiple types of potassium-aggravated myotonia. One type is called myotonia fluctuans, in which patients often experience short attacks of myotonia, usually about an hour long. The word “fluctuans” refers to the fact that in this disorder, the severity of myotonia attacks fluctuates. Some attacks are so mild that they can be worked off easily without causing much of a problem. Other attacks are stronger and more difficult to work off. Dealing with myotonia fluctuans can be confusing because of the inconsistent, unpredictable nature of the disorder.

There is another type of potassium-aggravated myotonia called myotonia permanens. As the name suggests, the disorder has a more “permanent” feeling — patients experience myotonia that is long-lasting and continuous. This type of myotonia tends to be severe, making it hard for patients to move because their muscles are constantly very rigid. The muscles contract too much, which causes them to feel rigid, and it also causes muscle enlargement. Patients’ muscles are large like a bodybuilder’s, but the muscles are actually weak. Breathing difficulties are another symptom of this disorder due to the myotonia affecting chest muscles. 

Acetazolamide-responsive myotonia is another type of potassium-aggravated myotonia. Patients who have this disorder have large, well-developed muscles that appear to be strong, but are weak in reality. This is caused by severe myotonia that constantly forces muscles to contract. This particular disorder is painful, even though not all types of myotonia are painful. The good news is that symptoms are responsive to the medication acetazolamide.

Triggers

A higher than normal blood potassium level is the main trigger for myotonia attacks, which is why the disorder is “potassium-aggravated.” Potassium-rich food is a major trigger. If a patient has both potassium-aggravated myotonia and hyperkalemic periodic paralysis, a high blood potassium level will trigger muscle weakness and paralysis attacks in addition to the myotonia attacks. The attacks of hyperkalemic periodic paralysis have additional triggers as well.

Resting after exercise is another trigger for potassium-aggravated myotonia attacks. Attacks are even more likely to happen if the exercise was especially strenuous. Attacks often happen within a half hour after the patient has stopped exercising and is resting. After having a period of rest, the patient finds that it is hard to move their muscles. This differs from another disorder, paramyotonia congenita, in which myotonia attacks happen during exercise, not after it. Another difference is the fact that people with paramyotonia congenita often experience myotonia that is triggered by cold, which isn’t the case with potassium-aggravated myotonia.

If you have potassium-aggravated myotonia and/or periodic paralysis, it can be helpful for you to have a trigger diary. After you have an attack, whether it’s an attack of muscle stiffness or muscle weakness, you should record in your trigger diary the time of the attack, which body parts were affected, whether you had weakness or stiffness, what you were eating or doing before the attack, how long the attack lasted, and what you did to recover from it. The diary will be very useful as time goes on because you’ll be able to read through it and discover your triggers.

Diagnosis

Symptoms of potassium-aggravated myotonia usually begin during infancy or childhood. This disorder is not progressive, which means that it does not gradually grow more severe as the patient ages. The problem is, however, that it often takes patients a long time to get properly diagnosed. Because the disorder is so rare, there are a lot of doctors who aren’t familiar with it, so they are likely to misdiagnose the patient with a more common disorder.

Getting the correct diagnosis is necessary to begin receiving effective treatments. Doctors must figure out which type of myotonia the patient has, and they need to determine whether or not the patient also has a periodic paralysis disorder such as hyperkalemic periodic paralysis. Sharing your family’s health history and your trigger diary with doctors can help them come closer to the correct diagnosis, and there are other diagnostic tools available, too.

Potassium-aggravated myotonia is a genetic disorder, and commercial lab genetic tests can be performed that can detect the disorder in some patients. However, genetic testing is not perfect and does not always detect all cases. A muscle biopsy is sometimes needed for doctors to diagnose periodic paralysis. This means that the doctor must remove and examine a small piece of the patient’s muscle tissue during or after an attack to see if the muscle tissue is abnormal. Another diagnosis method is the Compound Muscle Action Potential test, which measures the electrical activity of muscles. This test can’t always detect periodic paralysis, but it can do so in a lot of cases.

Treatment

The way potassium-aggravated myotonia is treated depends on whether or not the patient only has myotonia or they have both myotonia and muscle weakness attacks. Regarding myotonia attacks, mexiletine and lamotrigine are two medications that have worked to reduce this symptom in some patients. This is because they block the mutated sodium channels in muscle cell membranes.

Acetazolamide-responsive myotonia can be treated with the diuretic acetazolamide, which can also be useful to treat muscle weakness attacks in patients who have periodic paralysis. However, in some patients, acetazolamide makes weakness attacks worse, not better. Thiazide diuretics have also helped some periodic paralysis patients. The medication KEVEYIS (dichlorphenamide) is the only FDA-approved treatment for periodic paralysis. It has been proven to reduce weakness attacks.

There are some types of medications that people with potassium-aggravated myotonia should avoid: Beta2 agonists (such as fenoterol and ritodrine), monocarboxylic amino acids, and depolarizing muscle relaxants (such as suxamethonium/ succinylcholine/ diacetylcholine), which are often used in anesthesia.

There are other ways to manage this disorder besides medication. Patients should control their diet carefully in order to avoid eating foods that are high in potassium. They should also exercise in a way that isn’t overly demanding on the body. Patients who have myotonia and periodic paralysis should try to lower their day-to-day stress levels, stay away from cold areas, and look over their trigger diary to be aware of what kinds of other things trigger their muscle weakness attacks. 

Your Next Steps

If you think you may have potassium-aggravated myotonia, please talk with your doctor. Speaking with a doctor about a rare disorder can be intimidating, and many doctors have little to no prior knowledge about periodic paralysis. The PPA has many resources to help you become a better advocate for yourself. Click here to learn about other types of periodic paralysis. You can also submit a question to our Ask the Experts panel. Remember, we are here to support you all the way as you take action to advocate for your health!