Definition of Hyperkalemic periodic paralysis:

Hyperkalemic periodic paralysis is a disorder that involves occasional episodes of muscle weakness and, sometimes, higher than normal levels of potassium in the blood.

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

Causes, incidence, and risk factors:

Hyperkalemic periodic paralysis is due to faulty genes. In most cases, it is passed down through families (inherited). Occasionally, it occurs randomly in families. It is believed that the disorder is related to problems with the way the body controls sodium and potassium levels in cells.

Unlike other forms of periodic paralysis, persons with hyperkalemic periodic paralysis do not have low blood potassium levels. In fact, there may be normal or high levels of potassium in the bloodstream during and between attacks.

Risk factors include a family history of periodic paralysis. The condition occurs in approximately 1 in every 100,000 people. It affects men more often then women.

Symptoms:

The disorder involves 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 childhood. How often the attacks occur varies. Some people have several attacks a day. Attacks typically last only 1 to 2 hours, but can sometimes last as long as a day. They are usually not severe enough to need therapy. Some people have associated myotonia, in which they cannot immediately relax their muscles after use.

The weakness or paralysis:

• Most commonly occurs at the shoulders and hips
• May also involve the arms and legs but does not affect muscles of the eyes and those that help you breathe and swallow
• Most commonly occurs while resting after activity
• May occur on awakening
• Comes and goes
• Usually lasts 1 - 2 hours

Triggers may include:

• Resting after exercise
• Not eating (fasting)
• Exposure to cold
• Eating small amounts of potassium-rich foods or taking medicines that contain potassium

Signs and tests:

The health care provider may suspect hyperkalemic 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 high results of a potassium test.

Between attacks, a physical examination shows nothing abnormal. During an attack, muscle reflexes are 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.

The health care provider may run additional tests to rule out other causes.

Treatment:

The goal of treatment is to relieve symptoms and prevent further attacks.

Attacks are seldom severe enough to require emergency treatment. However, weakness can become worse with repeated attacks, so treatment to prevent the attacks should occur as soon as possible.

Glucose or other carbohydrates (sugars) given during an attack may reduce the severity of the symptoms. Calcium or diuretics, such as furosemide, may need to be given through a vein to stop sudden attacks.

Expectations (prognosis):

Sometimes attacks disappear later in life on their own. However, chronic attacks generally result in progressive muscle weakness that is present even between attacks.

Hyperkalemic periodic paralysis responds well to treatment. Treatment may prevent, and may even reverse, progressive muscle weakness.

Complications:

• Kidney stones (a side effect of acetazolamide)
• Heart arrhythmias during attacks (rare, not fatal)
• 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:

A medicine called acetazolamide prevents attacks in many cases. Thiazide diuretics such as hydrochlorothiazide are also effective and have fewer side effects than acetazolamide. A low potassium, high carbohydrate diet may also help prevent attacks, as may avoiding fasting, strenuous activity, or cold temperatures.