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Hypokalemic periodic paralysis

Definition

Hypokalemic periodic paralysis is an inherited disorder that causes occasional episodes of muscle weakness.

It is one of a group of genetic disorders that includes hyperkalemic periodic paralysis and thyrotoxic periodic paralysis.

Alternative Names

Periodic paralysis - hypokalemic

Causes, incidence, and risk factors

Hypokalemic periodic paralysis is a condition in which a person has episodes of muscle weakness and sometimes severe paralysis.

The condition is congenital, which means it is present from birth. In most cases, it is passed down through families (inherited) as an autosomal dominant disorder. That means only one parent needs to pass the gene related to this condition on to you in order for you to be affected.

Occasionally, the condition may be the result of a genetic problem that is not inherited.

Unlike other forms of periodic paralysis, persons with congenital hypokalemic periodic paralysis have normal thyroid function and very low blood levels of potassium during episodes of weakness. This results from potassium moving from the blood into muscle cells in an abnormal way.

Risks include having other family members with periodic paralysis. The risk is slightly higher in Asian men who also have thyroid disorders.

Disorders that cause intermittent episodes of paralysis as their primary effect are uncommon. Hypokalemic periodic paralysis occurs in approximately 1 out of 100,000 people.

Symptoms

The disorder involves attacks of muscle weakness or loss of muscle movement (paralysis) that come and go. Initially, there is normal muscle strength between attacks.

Attacks usually begin in adolescence, but they can occur before age 10. Attacks that do not begin until adulthood are rare in people with hypokalemic periodic paralysis and are usually caused by other disorders.

How often the attacks occur varies. Some people have attacks every day, while others have them once a year. Episodes of muscle weakness usually last between a few hours and a day.

The weakness or paralysis:

• Most commonly is located at the shoulders and hips
• May also affect the arms, legs, muscles of the eyes, and muscles that help you breathe and swallow
• Occurs intermittently
• Most commonly occurs on awakening
• Most commonly occurs after sleep or rest
• Is rare during exercise, but may be triggered by rest after exercise
• May be triggered by heavy, high-carbohydrate, high-salt meals or alcohol consumption
• Usually lasts 3 - 24 hours

Other symptoms may include:

• Eyelid myotonia (a condition in which after opening and closing the eyes, the patient cannot open them for a short time)

Note: The patient's thinking remains alert during attacks.

Signs and tests

Between attacks, a physical examination shows nothing abnormal. Before an attack, there may be leg stiffness or heaviness in the legs.

During an attack of muscle weakness, the blood potassium level is low. This confirms the diagnosis. There is no decrease in total body potassium, and blood potassium levels are normal between attacks.

During an attack, muscle reflexes may be decreased or absent, and muscles go limp rather than staying stiff. The muscle groups near the body, such as shoulders and hips, are involved more often than the arms and legs.

• An ECG or heart tracing may be abnormal during attacks.
• An EMG or muscle tracing is usually normal between attacks and abnormal during attacks.
• A muscle biopsy may show abnormalities.

Treatment

Muscle weakness that involves the breathing or swallowing muscles is an emergency situation. Dangerous heart arrhythmias may also occur during attacks.

The goals of treatment are relief of symptoms and prevention of further attacks.

Potassium that is given during an attack may stop the attack. It is preferred that potassium be given by mouth, but if weakness is severe, potassium may need to be given through a vein (IV). Note: Potassium, especially intravenous potassium, should be given with caution, especially in individuals with kidney disease.

Taking potassium supplements will not prevent attacks.

Avoiding alcohol and eating a low-carbohydrate diet may help.

A medicine called acetazolamide prevents attacks in many cases. If you take this medicine, your doctor may tell you to also take potassium supplements because acetazolamide may cause your body to lose potassium.

Triamterene or spironolactone may help to prevent attacks in people who do not respond to acetazolamide.

Support Groups

Expectations (prognosis)

Hypokalemic periodic paralysis responds well to treatment. Treatment may prevent, and even reverse, progressive muscle weakness. Although muscle strength is initially normal between attacks, repeated attacks may eventually cause worsening and permanent muscle weakness between attacks.

Complications

• Kidney stones (a side effect of acetazolamide)
• Heart arrhythmias during attacks
• Difficulty breathing, speaking, or swallowing during attacks (rare)
• Progressive muscle weakness

Calling your health care provider

Call your health care provider if you have intermittent muscle weakness, particularly if there is a family history of periodic paralysis.

Go to the emergency room or call the local emergency number (such as 911) if you faint or have difficulty breathing, speaking, or swallowing. These are emergency symptoms.

Prevention

Hypokalemic periodic paralysis cannot be prevented. Because it can be inherited, genetic counseling may be advised for couples at risk for the disorder.

Treatment prevents attacks of weakness. Before an attack, there may be leg stiffness or heaviness in the legs. Performing mild exercise when these symptoms start may help prevent a full-blown attack.

References

Barohn RJ. Muscle diseases. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 447.