Definition Familial periodic paralysis is a condition that causes occasional bouts of muscle weakness. It is usually brought on by an abnormal level of potassium in the blood.
What is going on in the body? Familial periodic paralysis is an inherited condition. The episodes usually begin during the teenage years. When the attack occurs, there may be an abnormally high or low level of potassium in the blood. The exact cause of this condition is not well understood.
What are the signs and symptoms of the condition? The episodes of weakness in familial periodic paralysis may occur often or rarely. The episodes may last a few hours or several days. The level of weakness that occurs can also vary from mild to severe. The arms, eyelids, and face muscles are commonly affected. In more serious cases, the swallowing or breathing muscles may be involved. During the episodes, the person is awake and aware of what is going on. Muscle strength is usually normal between these episodes. Repeated bouts of paralysis can cause a gradual loss of strength.
Other signs or symptoms may occur during the attacks of weakness, including:
an abnormally low or high level of potassium in the blood
What are the causes and risks of the condition? Familial periodic paralysis is usually an inherited condition. It may also occur randomly within certain families. It occurs in about 1 in 100,000 people. It is more common in Asian people and those who also have thyroid disorders.
The episodes of weakness usually occur after sleep or rest and rarely occur during exercise. Factors that increase the risk of having an attack in affected people depend on the type of periodic paralysis a person has. The condition is often split into three categories, based on the potassium level in the blood during attacks:
hypokalaemic, for low levels of potassium
normokalaemic, for normal levels
hyperkalaemic, for high levels
In the low potassium form of this condition, eating a meal that is high in carbohydrates or sodium may cause an attack of paralysis. People with the normal and high potassium forms of this condition are often sensitive to potassium. If these people eat a meal high in potassium, they may have an attack.
What can be done to prevent the condition? Familial periodic paralysis is an inherited condition so there is no prevention. Genetic counselling may be helpful to couples with a family history of this condition.
How is the condition diagnosed? The doctor often suspects familial periodic paralysis based on the person's history of the attacks and a family history of the condition. If an attack is witnessed, the doctor can detect the muscle weakness. A blood potassium level may be done.
When attacks are too rare to witness, the doctor may want to try to cause an attack. This involves giving glucose, a carbohydrate, to a person if the low potassium form of this condition is suspected. Those suspected of having the normal or high forms of this condition might be given potassium in an attempt to cause an attack.
Sometimes an electrocardiogram or ECG, a test that shows the electrical activity of the heart, may be abnormal during attacks. This is due to the abnormal potassium levels. A test called electromyography, or EMG, may also be done. This test looks at how well the nerves and muscles work.
A muscle biopsy may be done in some cases. This is a procedure in which a small piece muscle tissue is removed with a special needle. This piece, or biopsy sample, can then be sent to the laboratory for analysis. The muscle tissue is often slightly abnormal in this condition.
What are the long-term effects of the condition? Repeated attacks of familial periodic paralysis over time can cause muscle weakness even between episodes. This weakness may gradually get worse. However, this condition usually responds well to treatment. Treatment is important because it may prevent long-term muscle weakness and can even restore strength to the muscles.
What are the risks to others? A person with familial periodic paralysis may pass it on to his or her children.
What are the treatments for the condition? For those with the low potassium form of this condition, low carbohydrate, low sodium diets may help prevent attacks. Potassium may be given if an attack to slow or stop an attack. Usually, potassium is given as a pill or liquid, but intravenous potassium may be given for severe weakness. A medication called acetazolamide can help prevent attacks in many people.
A person with the normal or high potassium forms of this condition should follow a low potassium diet to help prevent attacks. If an attack does occur, a high-carbohydrate food, such as a snack high in sugar, may help stop or slow the attack. Acetazolamide is also used to help prevent attacks. Another class of medications called thiazide diuretics, or "water pills," can also be tried to help prevent attacks.
A person should be monitored and treated for any arrhythmias or difficulty breathing. These more serious signs are more common in the low potassium form of this condition.
What are the side effects of the treatments? All medications have possible side effects. Giving too much potassium can cause muscle weakness and arrhythmias. The other medications can cause allergic reactions, stomach upset, and salt imbalances.
What happens after treatment for the condition? Lifelong treatment of periodic familial paralysis is usually needed because this condition cannot be cured.
How is the condition monitored? Any change in the number of attacks or response to treatment should be reported to the doctor. The medications may need to be changed to improve symptoms or decrease side effects. A blood test may be done occasionally to monitor for salt imbalances from the medications. Any new or worsening symptoms should be reported to the doctor.
Author: James Broomfield, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 22/02/2005 Contributors Potential conflict of interest information for reviewers available on request
