Paramyotonia congenita

Alternative names
Hyperkalemic periodic paralysis; Periodic paralysis - hyperkalemic

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

Causes, incidence, and risk factors

The cause of hyperkalemic periodic paralysis is believed to be a genetic muscle disease. In most cases it is inherited directly; 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 not uncommon.

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 triggerd by cold expsoure or 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. (It 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 that are capable of carrying an electrical current, such as sodium and potassium.)

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 that 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       o Most commonly located in the shoulders and hips       o Arms and legs may also be involved       o Occurs intermittently       o May occur on awakening       o May be triggered by rest after exercise       o May be triggered by fasting       o May be triggered by cold exposure       o May be triggered by eating small amounts of potassium       o Usually lasts for less than 2 hours  
  • Spontaneous recovery of normal strength between attacks  
  • Normal alertness during attacks

Signs and tests

The health care provider may suspect hyperkalemic periodic paralysis based on other family members having the disorder, symptoms that come and go, normal or high results of a potassium test, and ruling 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 need to be given 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.

Expectations (prognosis)

Sometimes attacks resolve 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

Calling your health care provider
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.

Johns Hopkins patient information

Last revised: December 6, 2012
by Simon D. Mitin, M.D.

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