Hyperkalemic Periodic Paralysis (HyperKPP) is a rare inherited muscle disorder which causes episodes of paralysis or weakness. It's estimated to occur in only one of 250,000 individuals, though since it is inherited there may be several patients in a single family. It was only recognized as a separate disorder in 1955.
Attacks are usually brief (lasting minutes to an hour or two) any may vary from weakness or paralysis of a single limb to generalized paralysis. There may be muscle stiffness and pain and an irregular heartbeat. These episodes often occur during rest after exercise, and they may occur on awakening in the morning. Attacks may develop quite rapidly, causing unexpected falls. The muscle stiffness (medical term 'myotonia') may come and go or it may be more or less constant. In myotonia the muscle fibers are slow to relax after contraction. Some patients are very athletic in appearance due to the myotonia, 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.
During attacks of muscle weakness, potassium moves from the muscle cells into the blood, causing an imbalance in the ratio of potassium inside and outside muscle cells. This makes the cells unable to contract properly.
Ion channels are tiny pores (openings) that allow ions (molecules) of sodium and potassium to move through the cell membrane. This movement of sodium and potassium ions from one side of the muscle membrane to the other creates an electrical current. The periodic paralyses are caused by abnormalities in these ion channels (especially the sodium, calcium and potassium channels) of the muscle membrane. Hyperkalemic periodic paralysis is caused by a genetic mutation in a sodium channel in the muscle membrane. This mutation makes the person with HyperKPP sensitive to increases in serum potassium that wouldn't bother the average person. Anyone can be made weak by a drastic increase in serum potassium, but the person with HyperKPP gets weak with even a slight elevation in potassium level, and patients with HyperKPP may become profoundly paralyzed while their potassium levels remain well within normal limits, even when their potassium is on the lower end of normal.
The term 'hyperkalemic' is somewhat confusing, because in most patients the level of potassium in the blood does not rise above normal during attacks. 'Hyperkalemic' refers to the fact that attacks may be triggered by eating potassium-rich foods or by giving the patient potassium.
In a majority of cases HyperKPP is inherited, but a person may carry, and pass on, the defective gene without ever experiencing any symptoms at all. But some cases just happen, like any other birth defect, for reasons which are unclear.
The chances that a child of an affected person will inherit the defective gene is 'statistically' 50%, but not all who inherit the gene will have symptoms. 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 variety of tests are used. Since most episodes are brief it may be difficult to 'catch' a patient during a spontaneous episode. But several blood tests taken over a period of a week or two to measure the level of potassium in the blood may suggest the diagnosis, since potassium levels are frequently in the higher end of normal between attacks. Patients with HyperKPP often have an accompanying muscle condition called myotonia, which may be found during Electromyographic (EMG) examination. Evidence of myotonia supports the diagnosis of HyperKPP. At times diagnosis is not as easily accomplished, and further testing is necessary. There is more information about diagnosis in other articles on this website. See The Exercise EMG.
The best place for treatment is almost always the patient's own family physician, if that physician 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. Common illnesses can turn into life-threatening emergencies for a HyperKPP patient, and in these instances there is no time or opportunity to go to a far away specialist.
Some episodes of HyperKPP are triggered by food. Food triggers are generally those which are high in potassium. Fruits high in potassium include cantaloupes, apricots (fresh and dried) dried figs, kiwi fruit, peaches, raisins, banana and prunes. Fruit juices are high in potassium, especially orange and pineapple juice and apricot and peach nectars. High potassium vegetables include artichoke, parsnip, potato, pumpkin, spinach, broccoli, Brussel sprouts, cauliflower, tomato juice, tomato paste and V-8 juice. Lentils and beans are high in potassium. Other foods that are high in potassium include nuts, peanut butter and chocolate.
Other common triggers include both rest after activity and periods of inactivity (for example; sitting through a long class or church service, especially in a cool room). Sleep is a potent trigger. Going too long without eating is another trigger. HyperKPP patients can't let themselves get too hungry. Getting chilled is a trigger. Eating or drinking cold foods or beverages may provoke attacks in sensitive individuals. Weather changes seem to affect some HyperKPP patients adversely. Hydrocarbons like gasoline fumes, paint fumes or car exhaust have been reported as triggers by some patients. Drinking alcohol is another trigger for most HyperKPP patients.
HyperKPP episodes are often brief (minutes to an hour) and may not happen often, though some patients have several episodes per day. Patients learn that they have to stay warm, avoid unaccustomed heavy exercise, and not sit still too long at a time. Many find they can abort a developing episode by drinking a sweet beverage or eating some hard candy at the first sign of an attack. Unfortunately this can lead to weight gain.
Learn to determine your triggers and avoid them. For some people this is enough. For others medication is necessary.
A tablespoonful of Calcium Gluconate syrup stirred into a glass of Coca Cola or other sweet beverage may stop a mild episode in the early stages. Calcium Gluconate Syrup is a mineral supplement available off the shelf and is found in most pharmacies. Some patients find that drinking 1/4 cup of tonic water daily (available at the grocer's) helps ease symptoms. Albuterol, administered by nebulizer or inhaler, is an effective treatment for some patients. For those who have frequent episodes more aggressive treatment is advisable, especially since some patients with HyperKPP may develop permanent muscle weakness after years of episodes.
The carbonic anhydrase inhibitor 'Diamox' (acetazolomide) is often prescribed for HyperKPP patients. About 25% of patients do not respond to Diamox and must take other medication. Other medications used to treat HyperKPP include the potassium-wasting diuretics - Lasix (furosemide), Hydrodiuril (hydrochlorothiazide), etc. For those who have significant myotonia, the anti-arrhythmic drug Mexitil (mexiletine) is used in low doses; 50-150 mg daily is reported to be adequate by patients. Very low doses of Paxil (paroxetine) (10-20 mg daily) have also been reported to help relieve myotonia.
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.
Genetic testing is available, but it is not yet reliable enough to diagnose all HyperKPP patients. While a genetic test may be able to say you have HyperKPP, if the results of the test is negative that does NOT mean you do not have the disorder, as there are mutations which they have not yet been able to identify. If you plan to be tested it is wise to talk about this issue with your physician ahead of time, just in case your test comes back negative (as most are still doing at this point). Make certain you will not be denied therapy by your physician or HMO should the test be negative!
Most people with HyperKPP lead reasonably normal lives. Many cases of HyperKPP are mild, and even those who are severely affected can have their symptoms eased through medication and attention to diet and lifestyle issues. There is no cure, but most patients manage to lead well-rounded and fulfilling lives. There is no denying that some patients have physically-compromised lives, especially patients with a long history of frequent and severe episodes. But many are quite active. Members of our Listserv group come from all professions and walks of life including physicians, nurses, teachers, lawyers, musicians, engineers, journalists, farmers and ranchers, a plantation owner, homemakers, accountants, and computer specialists.
This is a hard question to answer. Permanent muscle weakness is a fact of life for many older patients, and activities like climbing stairs and walking long distances may become very fatiguing. Any number of our older members use a wheelchair or 'scooter' 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.
Several of our families have affected members who have lived well into their 80's, in complete control of their mental faculties and capable of independent life until the end of their lives. We hope we have answered some of your basic questions about Hyperkalemic Periodic Paralysis. For medical references see our Physician's Sheet: Hyperkalemic Periodic Paralysis.