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Hypokalemic periodic paralysis

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Hypokalemic periodic paralysis is a disorder that causes occasional episodes of muscle weakness and sometimes a lower than normal level of potassium in the blood.

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

Causes
Hypokalemic periodic paralysis is congenital. This means it is present at birth. In most cases, it is passed down through families (inherited) as an autosomal dominant disorder. In other words 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. But they have a very low blood level of potassium during episodes of weakness. This results from potassium moving from the blood into muscle cells in an abnormal way.

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

Symptoms
Symptoms include attacks of muscle weakness or loss of muscle movement (paralysis) that come and go. There is normal muscle strength between attacks.

Attacks usually begin in the teen years, but they can occur before age 10. How often the attacks occur varies. Some people have attacks every day. Others have them once a year. During attacks the person remains alert.

The weakness or paralysis: Other symptoms may include:
Exams and Tests
The health care provider may suspect hypokalemic periodic paralysis based on a family history of the disorder. Other clues to the disorder are muscle weakness symptoms that come and go with normal or low results of a potassium test.

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, blood potassium level is low. This confirms the diagnosis. There is no decrease in total body potassium. Blood potassium level is normal between attacks.

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

Tests that may be done include: Other tests may be ordered to rule out other causes.

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

Muscle weakness that involves the breathing or swallowing muscles is an emergency situation. Dangerous heart arrhythmias may also occur during attacks. Any of these must be treated right away.

Potassium given during an attack may stop the attack. Potassium can be taken by mouth. But if weakness is severe, potassium may need to be given through a vein (IV).

Taking potassium supplements will not prevent attacks.

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

A medicine called acetazolamide may be prescribed to prevent attacks. Your doctor may tell you to also take potassium supplements because acetazolamide may cause your body to lose potassium.

If acetazolamide does not work for you, other medicines may be prescribed.

Outlook (Prognosis)
Hypokalemic periodic paralysis responds well to treatment. Treatment may prevent, and even reverse, progressive muscle weakness. Although muscle strength starts out normal between attacks, repeated attacks may eventually cause worsening and permanent muscle weakness between attacks.

When to Contact a Medical Professional
Call your health care provider if you have muscle weakness that comes and goes, especially if you have family members who have periodic paralysis.

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

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

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

Alternative Names
Periodic paralysis - hypokalemic

References
Chinnery PF. Muscle diseases. In: Goldman L, Schafer AI, eds. Goldman’s Cecil Medicine . 24th ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 429.

Mount DB, Zandi-Nejad K. Disorders of potassium balance. In Taal MW, Chertow GM, Marsden PA, et al., eds. Brenner and Rector’s The Kidney . 9th ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 17.

Update Date: 11/7/2013
Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and /the A.D.A.M. Editorial team.
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