Frequently Asked Questions about Paramyotonia Congenita
What is Paramyotonia Congenita?
Paramyotonia congenita (PMC) is an autosomal dominant muscle disease characterized by what is called paradoxical myotonia defined as myotonia that appears during exercise and becomes much more severe upon exposure to cold. The myotonia which occurs during attacks of PMC may be so pronounced as to interfere with respiration and make voluntary movement difficult.
The medical term myotonia means that the muscle fibers are slow to relax after contraction. Myotonia can make it difficult for the patient to let go of objects which have been picked up (like a pen or drinking glass) or the muscles may feel tight or stiff. The muscles may ache. Some myotonic patients are very athletic in appearance, but appearances can be deceiving as these well-developed muscles are often quite weak. For some patients myotonia is painless, for others it is painful.
Some patients with PMC also have Hyperkalemic periodic paralysis, and in some patients PMC occurs alone. HyperKPP and PMC have been demonstrated to be caused by a mutation in the sodium channel on the same gene and are considered to be allelic (variant forms of the same disorder).
The difference between PMC and HyperKPP are: 1) PMC patients are usually extremely sensitive to cold exposure. 2) PMC patients develop rigidity as they exercise, not during rest after exercise. This is called 'paradoxical' myotonia - which is where 'Paramyotonia gets its name. 3) PMC episodes tend to last longer than HyperKPP episodes - days rather than hours. In some PMC patients long-term episodes (weeks to months) of significant weakness can be triggered by unusual exertion. Such patients must be extremely careful to avoid fatigue.
There can be a lot of variation in the symptoms of PMC, even among affected members in the same family. It's now been discovered that there are several types of PMC, determined by which of four amino acids substitutes itself for the 'proper' amino acid on the gene strand.
PMC can be associated with either HypoKPP or HyperKPP, but it appears more commonly in association with HyperKPP. There is a form of PMC called PMC Von Eulenburg in which episodes are triggered by a fall in potassium. Patients with HyperKPP may have this form of PMC, and thus may exhibit sensitivity to fluctuations of potassium in either direction. Treatments for PMC must be individualized depending on mutation and symptoms. Patients must learn to 'read' their symptoms and take the appropriate management steps to lower or raise potassium levels as needed. Managing PMC is probably the biggest challenge of all of the periodic paralyses and requires both flexibility and a team approach between patient and physician if the effort is to be successful.
What causes Paramyotonia Congenita?
PMC and HyperKPP are both caused by an abnormality in the sodium channel of the muscle membrane. This flaw makes the person with PMC extremely sensitive to cold, to the exchange of sodium and potassium ions which occurs during exercise and to shifts in potassium levels that wouldn't bother the average person. The person with PMC may get muscle stiffness and weakness with even slight changes in potassium level, or in response to cold or exercise.
No one in my family has this disease. How did I get it?
In a majority of cases PMC is inherited, but in some cases it just happens, like any other birth defect, for reasons which are unclear. It usually, but not always, accompanies HyperKPP.
Will I pass this on to my children and how does inheritance work?
The chances that a child of an affected person will inherit the defective gene is 'statistically' 50%, but the degree to which children are affected may vary from one child to the next. One child may be mildly affected, the next seriously affected and the next unaffected. Even identical twins may be affected to different degrees. A child with PMC is often affected from an early age.
What triggers attacks of PMC?
The Hyperkalemic forms may be triggered by potassium-rich food. Cantalopes, apricots, dried figs, kiwi fruit, peaches, raisins, banana and prunes are all high in potassium as are orange and pineapple juices and apricot and peach nectars. High potassium vegetables include; Artichoke, lentils and beans, parsnips, potato, pumpkin, spinach, broccoli, brussels sprouts, cauliflower, tomato juice/puree and V-8 juice. Most nuts are high in potassium as is peanut butter. Chocolate is also high in potassium.
Other triggers for PMC episodes include activity or exercise. Vigorous exercise may provoke weakness which lasts for months. Getting chilled will make most PMC patients weak. Weather changes trigger episodes in some patients.
There is more than one type of PMC. In some types patients must avoid potassium and in some forms they require potassium.
How can I determine what causes my attacks?
See How to Determine Episode Triggers.
How do I avoid having attacks?
Determine your triggers and learn to avoid them. For some people this is enough. For others medication is necessary.
What tests are used to diagnose PMC?
A frequently used test is the Electromyogram (EMG). During this test fine needles are inserted into the muscle and the electrical signals the muscles generate are recorded. The muscle is chilled for this test, as chilling brings on the instability of the muscle membrane. At times diagnosis is not as easily accomplished, and further testing is necessary. The subject of diagnosis is one which is somewhat complex, and is outside the scope of this discussion. For more information consider joining the on-line support group, HKPP Listserv.
Where do I go for the best treatment?
The best place for treatment is almost always the patient's own family physician, if that person is willing to read about the condition and learn how to manage it. Every patient responds a bit differently to treatment and the members of our group who are, on the whole, the most satisfied with their care are those who are cared for by the person who cares for their overall health.
Who is doing research on PMC?
There are a number of research teams working on the Pps. Research is concentrating on the genetics and mechanics of the channelopathies, rather than on therapy and management. There's been nothing new in the way of therapy for many years, although we have learned how to apply therapies much more effectively, and we've made great strides in management.
Can I have genetic test for PMC?
Genetic testing is available, but it is not yet reliable enough to diagnose all cases of PMC. While a genetic test may be able to say you have PMC, if the results of the test is negative that does NOT mean you do not have the disorder, as researchers know there are a number of variants which they have yet to be able to identify.
What medications are prescribed for PMC?
The medications prescribed depend on the type of PMC the patient has, and if the patient has another type of periodic paralysis as well as PMC. The carbonic anhydrase inhibitor 'Diamox' (acetazolomide) is often prescribed for the other periodic paralyses, but it tends to make many PMC patient's symptoms worse.
Patients who take carbonic anhydrase inhibitors must be alert to potentially dangerous drug interactions as they slow the excretion of other drugs from the system. Avoid large doses of aspirin when taking Diamox or Daranide.
Some other commonly used drugs to be cautious with when taking Diamox or daranide include barbiturate medicines used for inducing sleep or treating seizures, the ephedrines (found in some over the counter asthma inhalers) the heart drug Mexitil (mexiletine) which is often prescribed in HyperKPP and PMC for myotonia, steroids and diuretic medications ('water pills').
This is not an exhaustive list. Always discuss all other medications you are taking with your physician when starting a new drug.
Diuretics which cause the kidneys to excrete potassium are often used in PMC, especially when it is accompanied by HyperKPP. These are drugs like the thiazides (Hydrodiuril, hydrochlorothiazide) or furosemide (Lasix). Florinef is used occasionally when the patient needs to retain sodium and fluid as well as excrete potassium. Low doses of Mexiletine (Mexitil) and Paxil (paroxetine) are used to help reduce myotonia. Potassium supplementation often is helpful in cases of PMC, even when patients must take diuretics to help them excrete potassium.
Will I be able to lead a normal life?
Most people with PMC lead reasonably normal lives, though they must be cautious not to get chilled or overextend themselves physically. Many cases are mild, and even in those with more persistent episodes medication and attention to diet and lifestyle issues can go a long way toward easing symptoms. There is no cure, but most patients manage to lead well-rounded and fulfilling lives. There is no denying that PMC does require adaptations to many patient's lives, but by itself it does not cause permanent muscle damage.
Will my life be cut short?
There is no evidence that PMC is life-threatening.
Will I end up in a wheelchair?
This is a hard question to answer. If activities like climbing stairs and walking long distances become very fatiguing it may be wise to use a chair to conserve physical strength and avoid falls. Any number of our older members use a wheelchair outside the home, but are mobile and on their feet inside the house. Very few rely on a wheelchair full time unless their condition is complicated by other problems.
We hope we have answered some of your basic questions about Paramyotonia Congenita. For medical references see our Physician's Sheet: Paramyotonia Congenita.