Hyperkalemic periodic paralysis

Alternative names:

adynamia episodica hereditaria; periodic paralysis - hyperkalemic

Definition:

A disorder that causes intermittent episodes of muscle weakness. Attacks can be triggered by administration of potassium.

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 sporadically in a family group.

The disorder involves attacks of muscle weakness or paralysis, alternating with periods of normal muscle function. Attacks usually begin very early in life, often before the age of one year. Attacks are usually frequent, but last for only 1 or 2 hours. They tend to occur while resting after exercise or exertion.

Unlike disorders that cause intermittent weakness as the primary symptom (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 high or normal levels of potassium in the bloodstream both 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 the other disorders, have no effect on hyperkalemic periodic paralysis. Administration of potassium, which is used to treat weakness associated with the other disorders, worsens the weakness.

The elevation of serum potassium seldom is 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 abnormalities of the muscle cell wall and the mechanisms by which 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 episodes of paralysis or weakness is a symptom of another disorder. Hyperkalemic periodic paralysis occurs in approximately 1 out of 100,000 people. Men are affected more often than women and usually have more severe symptoms.