Adynamia episodica hereditaria

Adynamia episodica hereditaria

Description, Causes and Risk Factors:

Adynamia episodica hereditaria first described in 1955 is a rare muscle disease with autosomal dominant inheritance. Clinically it is similar to the much more common hypokalemic periodic paralysis; however, during episodes of muscle weakness the serum potassium rises rather than falls.

adynamia episodica hereditaria

Three variants of adynamia episodica have been described: (1) in combination with clinical or electromyographical myotonia without any signs of myotonia and in and combination with paramyotonia. The latter variant has also been called paralysis periodic paramyotonica. The affected members of a given family always show the same variant.

Adynamia episodica hereditaria is congenital, which means it is present from before 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 passed down through families.

It is believed that the disorder is related to problems with the way the body controls sodium and potassium levels in cells.

Researchers believe mutation in the SCN4A gene mainly cause adynamia episodica hereditaria. The SCN4A gene provides instructions for making a protein that plays an essential role in muscles used for movement (skeletal muscles). For the body to move normally, these muscles must tense (contract) and relax in a coordinated way. Muscle contractions are triggered by the flow of certain positively charged atoms (ions), including sodium, into muscle cells. The SCN4A protein forms channels that control the flow of sodium ions into these cells.

Mutations in the SCN4A gene alter the usual structure and function of sodium channels. The altered channels cannot properly regulate the flow of sodium ions into muscle cells, which reduces the ability of skeletal muscles to contract. Because muscle contraction is needed for movement, a disruption in normal ion transport leads to episodes of muscle weakness or paralysis.

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 than women.

RESEARCH: The cause of weakness was investigated in a patient with adynamia episodica hereditaria without myotonia. A pattern of exercise and rest produced episodes of hyperkalemic periodic paralysis. In addition, local muscle weakness was induced by forearm cooling. Investigations on isolated intercostal muscle demonstrated that a high potassium concentration in the bathing solution triggered a non-inactivating membrane current causing depolarization of the muscle fibers. This current was carried by sodium as it could be inhibited by tetrodotoxin. The abnormal sodium conductance led to an increase of sodium within the fibers. This was demonstrated directly by intracellular recordings. Weakness induced by rest after exercise and cold-induced weakness appeared to have different pathomechanisms. In the cold, the muscle fibers retained a normal resting potential, but their excitability was reduced and their mechanical threshold was increased. These findings also provide evidence that the mechanism of cold-induced weakness in adynamia episodica is distinctly different from the cold-induced weakness that occurs in paramyotonia congenita.


    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.


The healthcare provider may suspect adynamia episodica hereditariabased 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. Persons with adynamia episodica hereditariamay have normal or high levels of potassium in the bloodstream during and between attacks.

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 healthcare provider may run additional tests to rule out other causes.


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.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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