Hypokalemic periodic paralysis is a condition of intermittent episodes of muscle weakness and sometimes severe paralysis. It is one of a group of genetic disorders that includes hyperkalemic periodic paralysis and thyrotoxic periodic paralysis.

This disorder is distinguished from other forms of periodic paralysis in that people with this disorder have normal thyroid function and very low blood levels of potassium during episodes of weakness.

Hypokalemic periodic paralysis is a congenital (present from birth) condition. It can be inherited but occasionally occurs as a result of a non-inherited genetic mutation that affects just the sperm or the egg cell. In most cases, it is inherited as an autosomal dominant disorder (only one parent must transmit the gene for the baby to be affected).

The disorder involves attacks of muscle weakness or paralysis alternating with periods of normal muscle function. Attacks usually begin in adolescence, but they can occur before age 10. Attacks of intermittent weakness that do not begin until adulthood are rare and are usually caused by other disorders.

The frequency of attacks varies from daily to yearly. Episodes of muscle weakness usually last between a few hours and one day. Other forms of periodic paralysis may last longer.

During an attack of muscle weakness, there is a low level of potassium in the bloodstream. Serum potassium levels are normal between attacks. There is no decrease in total body potassium, however. Potassium flows from the bloodstream into muscle cells during attacks.

Insulin levels may affect the course of the disorder in some people because insulin increases the flow of potassium into cells.

Weakness most commonly affects the muscles of the arms and legs, but it may occasionally affect the eye muscles or the muscles involved in breathing and swallowing (which can be fatal).

Although muscle strength is initially normal between attacks, repeated attacks may eventually cause worsening and permanent muscle weakness between attacks.

Attacks may be triggered by eating meals high in carbohydrate or salt, or by consuming alcohol. Attacks most commonly occur after sleep or rest and are rare during exercise, but rest after an exercise period may trigger an attack. The risk is slightly higher in Asian men who also have thyroid disorders (thyrotoxic periodic paralysis).

Risks include having other family members with periodic paralysis.

Disorders that cause intermittent episodes of paralysis as their primary effect are uncommon. Hypokalemic periodic paralysis occurs in approximately 1 out of 100,000 people. Men are affected more often than women and usually have more severe symptoms.

• Weakness or paralysis
  • Most commonly located at the shoulders and hips
  • Involves the arms and legs
  • Occurs intermittently
  • Most commonly occurs on awakening
  • May be triggered by rest after exercise
  • May be triggered by heavy, high-carbohydrate, high-salt meals or alcohol consumption
  • Usually lasts less than 24 hours
• Normal muscle strength between attacks
• Positive Babinski's reflex
• Eyelid spasms between episodes

The health care provider may suspect hypokalemic periodic paralysis if the symptoms come and go, potassium levels are low during attacks, and other disorders known to cause low potassium are not suspected. Hypokalemic periodic paralysis is also likely if other family members have the disorder.

Between attacks, a physical examination shows nothing abnormal. Before an attack there may be leg stiffness or heaviness in the legs. Performing mild exercise when these symptoms start may help prevent a full blown attack.

During an attack, muscle reflexes may be 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.

The health care provider may attempt to trigger an attack to aid in diagnosis by reducing potassium levels through administration of insulin and glucose.

• Serum potassium is low during attacks but normal between attacks (confirming the diagnosis of hypokalemic periodic paralysis).
• 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.

• Kidney stones (a side effect of acetazolamide)
• Heart arrhythmias during attacks
• Difficulty breathing, speaking, or swallowing during attacks (rare)
• Progressive muscle weakness

Hypokalemic periodic paralysis cannot be prevented. Because it can be inherited, genetic counseling may be advised for couples at risk for the disorder.

Treatment of hypokalemic periodic paralysis prevents attacks of weakness.