Familial periodic paralysis

Causes and Risks:
Familial periodic paralysis is a condition of intermittent episodes of paralysis or muscle weakness that occurs in multiple members of a family group. Many (but not all) cases of familial periodic paralysis are termed "hypokalemic" periodic paralysis.

Hypokalemic periodic paralysis occurs as an inherited condition. In most cases, it is inherited as an autosomal dominant disorder (only one parent must transmit the gene). In other cases, the disorder appears sporadically in a family group.

The disorder involves attacks of muscle weakness or paralysis alternating with periods of normal muscle function. Attacks usually begin in adolescence but can occur before age 10. Attacks of intermittent weakness that do not begin until adulthood are rare and usually caused by other disorders. The frequency of attacks varies from daily to yearly. Episodes of muscle weakness may last for a few hours or persist for several days.

During an attack of muscle weakness, there is a low level of potassium in the bloodstream (serum). Serum potassium levels are normal between attacks. There is no decrease in total body potassium, however. Potassium flows from the bloodstream into muscle cells. Insulin levels may affect 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 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 progressive and persistent muscle weakness between attacks.

Risks include a family history of periodic paralysis. Attacks may be triggered by ingestion of high carbohydrate meals. 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 ).

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

Prevention:
Genetic counseling may be advised. Treatment of familial periodic paralysis prevents attacks of weakness .

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
    • may last for several days

  • spontaneous recovery of normal strength between attacks
  • positive Babinski's reflex

Note : The patient's thinking remains alert during attacks.

Signs and Tests:
The health care provider may suspect familial periodic paralysis based on a family history of the disorder, the episodic nature of symptoms, demonstration of low-potassium levels during attacks, and elimination of other disorders associated with low-potassium as the cause of symptoms.

Between attacks, the examination is normal. During an attack, reflexes may be decreased or absent. Weakness is flaccid rather than spastic and is greater in the proximal muscle groups (near the body, such as shoulders and hips) than in the distal groups (away from the body, such as the arms and legs). The health care provider may attempt to trigger an attack by reducing potassium levels through administration of insulin and glucose.

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

An ECG may be abnormal during attacks. An EMG is normal. A muscle biopsy may occasionally show abnormalities.

Treatment:
Muscle weakness that involves the breathing or swallowing muscles is an emergency situation. Dangerous heart arrhythmias may also occur during attacks.

The goals of treatment are relief of acute symptoms and prevention of further attacks.

Potassium that is given during an attack may stop the attack. It is preferred that potassium be given by mouth, but if weakness is severe, intravenous potassium may be necessary. (Note: intravenous potassium should only be given if kidney function is adequate and the person is monitored in the hospital.) Administration of potassium will not prevent attacks.

A low carbohydrate diet may be recommended.

Acetazolamide prevents attacks in many cases, possibly by reducing the flow of potassium from the bloodstream into the cells of the body. Potassium supplements may be necessary because acetazolamide may cause the body to excrete potassium.
Triamterene or spironolactone may help to prevent attacks in people who do not respond to acetazolamide.

Prognosis:
Chronic attacks will eventually result in progressive muscle weakness that is present even between attacks. Familial periodic paralysis responds well to treatment. Treatment may prevent, and may even reverse, progressive muscle weakness.

Complications:



Call Your Healthcare Provider:
Call your health care provider if you have intermittent muscle weakness , 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 you faint or have difficulty breathing , speaking, or swallowing. These are emergency symptoms.