Hyperkalemic periodic paralysis is associated with elevated levels of potassium in the bloodstream. The disorder causes occasional episodes of muscle weakness.

The cause of hyperkalemic periodic paralysis is believed to be a genetic muscle disease. In most cases it is inherited directly (from parent to child); in other cases, it occurs randomly in a family group.

The disorder involves attacks of muscle weakness or paralysis, alternating with periods of normal muscle function. Attacks usually begin in early childhood. Multiple daily attacks are possible.

Attacks typically last only 1 to 2 hours, but can sometimes last as long as a day. They tend to occur while resting after exercise or exertion. Attacks may also be triggered by exposure to cold, or by eating small amounts of potassium.

Unlike other forms of periodic paralysis (such as familial periodic paralysis and thyrotoxic periodic paralysis), hyperkalemic periodic paralysis is not associated with low potassium in the bloodstream (serum potassium). In fact, there may be normal or high levels of potassium in the bloodstream during and between attacks. The condition may be termed "normokalemic periodic paralysis" if potassium is normal during attacks.

Glucose and insulin administration, which trigger attacks of other forms of periodic paralysis, do not trigger attacks of hyperkalemic periodic paralysis. Giving potassium, which is used to treat weakness associated with the other disorders, worsens the weakness in this case.

The serum potassium levels are usually not at the level that would be expected to cause paralysis. The potassium level may remain normal or only very slightly elevated. It is thought that the disorder is caused by problems with the muscle cell wall and the way the body controls electrolyte levels in the cell (electrolytes are molecules, such as sodium and potassium, that are capable of carrying an electrical current.

Weakness most commonly affects the muscles of the arms and legs. Heart arrhythmias may occasionally develop during attacks. Although muscle strength is initially normal between attacks, repeated attacks may eventually cause progressive and persistent muscle weakness between attacks.

Risks include a family history of periodic paralysis. Attacks may be triggered by fasting. Attacks seldom occur during exercise but may be triggered by rest following exercise.

Disorders such as hyperkalemic periodic paralysis, which cause intermittent episodes of paralysis as their primary effect, are uncommon. More commonly, an intermittent episode of paralysis or weakness is a symptom of another disorder.

Hyperkalemic periodic paralysis occurs in approximately 1 in every 100,000 people. Men are affected more often than women and usually have more severe symptoms.

• Weakness/paralysis
  • Most commonly located in the shoulders and hips
  • Arms and legs may also be involved
  • Occurs intermittently
  • May occur on awakening
  • May be triggered by rest after exercise
  • May be triggered by fasting
  • May be triggered by exposure to cold
  • May be triggered by eating small amounts of potassium
  • Usually lasts for less than 2 hours
• Return to normal strength between attacks
• Normal alertness during attacks (no confusion or loss of consciousness)

The health care provider may suspect hyperkalemic periodic paralysis based on a family history of the disorder. Other clues to the disorder are symptoms that come and go and normal or high results of a potassium test. The health care provider will also run tests to rule out other disorders as the cause of intermittent weakness.

Between attacks, examination is normal. During an attack, the following may be observed:

• Reflexes may be decreased or absent
• Weakness is flaccid (loose) rather than spastic (tight)
• Weakness is greater in proximal muscle groups (near the body, such as shoulders and hips) than in distal groups (away from the body, such as arms and legs)

Attacks are not triggered by tests that reduce serum potassium (such as giving insulin and glucose), but may be triggered by giving potassium. Serum potassium is normal or high during attacks and may be normal or high between attacks.

The goals of treatment are relief of acute symptoms and prevention of 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. Intravenous calcium or diuretics such as furosemide may be needed to stop sudden attacks. Intravenous glucose and insulin cause potassium to move into the cell and may reduce weakness without a loss of total body potassium.

A high-carbohydrate diet may be recommended.

Acetazolamide, a medication that prevents attacks of familial periodic paralysis, is also effective in preventing attacks of hyperkalemic periodic paralysis. Thiazide diuretics such as chlorothiazide are also effective and have fewer side effects than acetazolamide.

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.

• 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

Call your health care provider if intermittent muscle weakness occurs, 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 fainting, difficulty breathing, difficulty speaking or difficulty swallowing occur. These emergency symptoms are rare.

Treatment prevents attacks of weakness.